Natural Hazards

, Volume 57, Issue 2, pp 185–212 | Cite as

Impacts on agriculture following the 1991 eruption of Vulcan Hudson, Patagonia: lessons for recovery

  • Thomas Wilson
  • Jim Cole
  • Shane Cronin
  • Carol Stewart
  • David Johnston
Original Paper

Abstract

Large explosive eruptions have the potential to distribute heavy ashfalls across large areas, resulting in physical and chemical impacts on agriculture, and economic and psycho-social impacts on rural communities. This study investigates how affected agriculture and rural communities have adapted, absorbed and mitigated impacts following a range of ashfall thicknesses (>2 m–<1 mm) from the 12–15 August 1991 eruption of Vulcan Hudson, one of the largest eruptions of the twentieth century. An estimated 1 million livestock died after the eruption due to pasture burial by ashfall and ongoing suppression of vegetation recovery. Horticulturalists suffered ongoing damage to crops from wind-blown ash and changes to soil properties increased irrigation and cultivation requirements. Real or perceived impacts on human health and impacts on farm productivity from the ashfall resulted in evacuation of farms and small towns in the short term. Long-term farm abandonment occurred in areas of heavy ashfall (upper Ibáñez valley) and highly stressed farming systems, even where ashfall was relatively thin (<50 mm), such as the Argentine steppe. The mono-agricultural system of sheep farming in the steppe region had few options other than destocking, proving less resilient than the diverse high-intensity horticultural and pastoral mix in irrigated valleys, which allowed more rapid adaption through diversification of production. Farms with natural advantages and greater investment in capital improvements led to greater damage potential initially (at least in cost terms), but ultimately provided a greater capacity for response and recovery. Better soils, climate and significantly greater access to technological improvements such as cultivation tools, irrigation and wind breaks were advantageous, such as at Chile Chico (Chile), Los Antiguos and Perito Moreno (Argentina). Cultivation increased chemical and physical soil fertility, especially when used in combination with fertilisation and irrigation. Appropriate use of seeds and cropping techniques within the new soil and growing conditions was important. Government agencies had a vital role in the dissemination of information for appropriate farm management responses, ash chemistry analysis, evacuations and welfare, and in the longer term to provide technical and credit assistance to facilitate recovery.

Keywords

Hudson Agriculture Ashfall impacts Recovery Volcanic hazards 

1 Introduction

Large explosive volcanic eruptions have the potential to distribute heavy ashfalls across large areas of agricultural land. Volcanic soils are often physically and chemically suited for crop growth and long-repose periods between eruptions in combination with land-use pressure, makes agriculture a common land use in volcanic regions (Cronin et al. 1998; Annen and Wagner 2003). All forms of agricultural production are vulnerable to physical and chemical effects of volcanic ashfall, with impacts on vegetation, soils, animal health, human health and essential infrastructure having been recorded (Table 1) (Blong 1984; Neild et al. 1998; Cronin et al. 1998; Ort et al. 2008). Light ashfalls have caused slight-to-severe pastoral, horticultural and livestock damage, but typically falls of <50 mm generate only short-term damage. Ashfalls >100 mm have resulted in abandonment of farmland, both temporarily and permanently and frequently led to long-term changes to agricultural land use (Table 1).
Table 1

Selected volcanic ashfall impacts on agriculture compiled from the literature

Eruption (year is AD)

Impacts

Reference

Hekla, Iceland (1104)

Approximately 2.0 km3 (bulk rock) of rhyodacite tephra fall covered >50,000 km2. Farms impacted by tephra deposits >250 mm (compacted) were never resettled. Exposed, marginal farms impacted by tephra deposits ~100 mm (compacted) were permanently abandoned

Thorarinsson (1979)

Hekla, Iceland (1693)

Approximately 0.18 km3 (bulk rock) of andesitic tephra fall covered ~22,000 km2. Farms impacted by tephra deposits >250 mm were never resettled. Farms impacted by 150 mm were abandoned for 1–4 years. Significant livestock losses (starvation and fluoride poisoning) and damage to cultivated fields were recorded within the 30 mm isopach

Thorarinsson (1979)

Vulcan Paricutin, Mexico (1943–1956)

Approximately 1.3 km3 (bulk rock) of scoria fall covering ~300 km2 to thicknesses >150 mm killed nearly all plant life within 5–8 km of the cone within the first year. Tephra deposits <100–250 mm could be manually removed or ploughed into the underlying soil. Deposits >250 mm could not be cultivated for many years

Rees (1979), Fisher et al. (1997) and Ort et al. (2008)

Hekla, Iceland (1970)

Approximately 0.66 km3 (bulk rock) of andesitic ash was erupted and deposited over 40,000 km2. Pastures were contaminated with extremely high levels of Fluorine from relatively thin ashfall (≤10 mm). Several thousand sheep died from acute fluorosis in west Hunavatnssysla and parts of Arnessysla

Georgsson and Pétursson (1972) and Thorarinsson (1979)

Mt St Helens, USA (1980)

Over 1.5 km3 of dacitic pyroclastic material (bulk rock) was erupted and dispersed ash ≥1 mm across 391,000 km2. Ash-covered and buried pastures and crops resulting in an estimated $US 100 million at the time ($US 157 million in 2009). Cultivation was used to break up ash deposits, increasing cultivation crop production costs and increasing machinery wear. Few beneficial elements were available for soils. Ash on plant surfaces reduced photosynthesis by up to 90%. Pollinator insects were dehydrated by suspended ash particles and suffered high mortality rates

Cook et al. (1981), Johansen et al. (1981), Folsom (1986) and Lyons (1986)

Mt Pinatubo, Philippines (1991)

Over 5 km3 of dacitic pyroclastic material (bulk rock) was erupted and dispersed tephra ≥10 mm across 7,500 km2 (on land). Over 962 km2 of agricultural land was seriously affected by ashfall; with damage to crops, livestock and fisheries estimated at 1.4 billion pesos ($US 86 million in 2009). Damage from lahar inundation was estimated at 778 million pesos ($US 45 million in 2009). Ashfall and lahar inundation caused major changes of land use and relocation of thousands of farmers

Mercado et al. (1996)

Mt Ruapehu, New Zealand (1995–1996)

Thin basaltic-andesite ashfalls (total bulk volume of 0.03 km3) covered pastures, preventing or restricting livestock feeding (<5 mm). After eating ash-covered pastures, >2,000 sheep died from starvation and acute fluorosis. Ashfall added between 30 and 1,500 kg ha−1 of sulphur to >25,000 km2 of land in primary production. Smaller amounts of selenium and in places potassium and magnesium were added to pastures, and this was beneficial for pasture growth

Cronin et al. (1995, 1998, 2003), Neild et al. (1998) and Johnston et al. (2000)

In eruption column, figure given in brackets is year of eruption; volumes given under impacts are bulk volumes

Assessing the impacts on farming from ashfall is more complex than simply analysing the thickness of ash versus the intensity or degree of impact. The frequency, duration and magnitude of the ashfall event, along with ash characteristics such as grain size, mineralogy and content of soluble acidic salts associated with the ash, are important controls on the nature and level of impact (e.g. Cook et al. 1981; Folsom 1986; Cronin et al. 1998, 2003; Witham et al. 2005; Ort et al. 2008). Of equal importance is the resilience of the farming unit, and its dependency on economic, environmental, social and political variables (Reycraft and Bawden 2000). The unique interaction of all these variables determines the level of socio-economic loss and disruption to agriculture and rural communities for each event (Ort et al. 2008). Contemporary studies (Table 1) have catalogued impacts of volcanic eruptions on agriculture, but these are generally after small eruptions, and few studies have investigated the impacts and recovery of modern agriculture following thick (>100 mm) and widespread ashfall. This is in part due to the low frequency of large eruptions and the lack of longitudinal volcanic impact studies, which track recovery for years to decades after an eruption (Lyons 1986).

This study investigates how affected agriculture and rural communities have adapted, absorbed and mitigated impacts following the 12–15 August 1991 eruption of Vulcan Hudson with information collected during early 2008. Field work in January to February 2008 was concentrated in southern Patagonia. Farming communities were visited in a transect from the upper Río Ibáñez valley in Chile, which received over a metre of ash, to the Atlantic coast of Santa Cruz province, Argentina, at the distal end of the ashfall deposit (Fig. 1). Field methods included semi-structured interviews with 32 farmers and 11 municipal officials and agricultural and animal experts (e.g. soil scientists and veterinarians) who had experienced the eruption and/or participated in the response and recovery operations. The interview schedule was designed to record their recollections of the characteristics of the ashfall, the impact ashfall had on the productivity of farming, the duration of impacts and any mitigation measures employed. The study also attempted to assess the long-term recovery of each farming operation and the factors which assisted or hindered recovery. Details of these interviews are available in Wilson et al. (2010b). Soil and ash deposits were also collected from sites at intervals along the longitudinal axis of the plume (Fig. 2) to determine residual ash grain size and thicknesses, and the fertility of recovered soils.
Fig. 1

Location map and isopach map for 1991 tephra-fall deposits (thickness is original and not compacted) of eruptive deposits; area of Fig. 2 is shown as dashed line (after Scasso et al. 1994). Numbers 30 and 31 refer to study farm sites listed in Table 2

Fig. 2

Enlargement of proximal–medial area affected by the 1991 tephra-fall deposit, showing the study farm sites (1–29) listed in Table 2 for this area (after Scasso et al. 1994)

2 1991 eruption of Vulcan Hudson

Hudson volcano (45°54′S; 72°58′W) is part of the Chilean Southern Volcanic Zone (33–46°S) located in southern Chile (Kratzmann et al. 2008). At least 12 Holocene explosive eruptions have occurred at Hudson, the most significant of which was at 6,700 years BP, 3,600 years BP, and in 1991 (Naranjo and Stern 1998). The 1991 eruption consisted of two separate, partially sub-glacial phreatoplinian explosive phases on 8–9 August and 12–15 August 1991. The 1991 eruption is noted for abruptly changing from basalt/basaltic-andesite magma composition in the first phase to trachyandesite and rhyodacite during the much larger second phase (Naranjo et al. 1993; Bitschene and Fernandez 1995; Kratzmann et al. 2008).

The first phase of the eruption dispersed ash to the north. The second phase dispersed ash over a narrow, elongated ESE sector of Patagonia, covering a land area of >100,000 km2 (Fig. 1) (Scasso et al. 1994). The eruption produced 4.3 km3 bulk volume (2.7 km3 dense rock equivalent) of tephra-fall deposits, making it one of the largest explosive eruptions of the twentieth century (Kratzmann et al. 2008). The elongated shape of the deposit was the result of strong northeasterly winds during the 12–15 August eruption. The prevailing strong westerly winds (known as the ‘roaring forties’) were supplemented at high levels by a jet stream blowing to the southeast in the upper troposphere-lower stratosphere at estimated speeds of up to 240 km per h (Scasso et al. 1994).

3 Impacts of the 12–15 August 1991 Hudson eruption

Pastoral farms with sheep and cattle, horticultural farms in irrigated river valleys, and rural service towns were impacted by the eruption. An estimated 1 million sheep and thousands of cattle died in Chile and Argentina, as a result of the heavy ashfalls burying feed, exacerbated by strong wind remobilisation of ash and the already poor health condition of the grazing stock (Valdivia 1993; Rubin et al. 1994; Inbar et al. 1995; Wilson et al. 2010b). Various authors reported regional-scale impacts on farming in the study region following the event (e.g. Banks and Ivan 1991; Bitschene et al. 1993; Bitschene and Mendia 1995; Inbar et al. 1995). This study offers a more detailed analysis of farm impacts across the region and over a longer timescale of recovery.

Almost immediately after the eruption, primary ash deposits were reworked by strong winds in southern Patagonia, producing severe and ongoing “ash storms”, extending the ashfall-like conditions for months to years (Scasso et al. 1994; Inbar et al. 1995; Wilson et al. 2010c). Impacts on and mitigation of these post-eruption ash storms are described in Wilson et al. (2010c) and complement this study.

The emergency response was initially clouded by fears of fluoride poisoning, following high recorded levels in the initial 8–9 August basaltic ash fall (Banks and Ivan 1991). As the composition of erupted magma changed to trachyandesite and rhyodacite, the content of soluble toxic salts decreased significantly (Banks and Ivan 1991; Rubin et al. 1994). This change and apparently conflicting information created major confusion amongst farmers and rural communities about the safety of ash-covered vegetation and water supplies during phase 2.

Interviewees in all cases reported they received greater ashfall thicknesses than those estimated by published sources (Table 2) (e.g. Naranjo et al. 1993; Scasso et al. 1994). When ash deposits were checked in the field 17 years after eruption, they generally agreed with published sources, where not eroded by wind or fluvial processes. We attribute the high farmer-estimated ash thicknesses to including both ash and snowfall thicknesses (reported to be contemporaneously deposited), and to local thickening, dune forms, post-depositional settling and erosion of the ash before they could be measured (Folsom 1986; Lyons 1986).
Table 2

Impact data for the 32 farms where farmers were interviewed

Farm ID

Location

Farm type

Ash thickness (mm)

Hectares

Livestock losses in 1991 (losses)

Loss notes

Farmer Est.

Naranjo et al. (1993)

Cows

Sheep

Other

1

Ibanez Valley

Pastoral

150–200

300

200

   

Not present at eruption—arrived 1994

2

Ibanez Valley

Pastoral

1,000

n/a

120

24 (9)

  

Evacuated 15 cows—sold for 40,000P but had been worth 100,000P

3

Ibanez Valley

Pastoral

1,500

1,000

170

33 (33)

   

4

Ibanez Valley

Pastoral

1,000–1,500

500

100

30 (15)

  

Evacuated cows—sold

5

Ibanez Valley

Pastoral

1,000–1,200

400

220

40 (20)

100 (100)

 

Evacuated cows—sold

6

Ibanez Valley

Pastoral

500–600

100

160

2 (2)

300 (200)

  

7

Puerto Ibanez

Mixed

50–200

40

150

100 (20–30?)

200 (170)

 

Crops inundated by lahars and dunes; 30 sheep evacuated; cows sold

8

Puerto Ibanez

Mixed

150–200

40

100

30 (2–5?)

  

Crops all covered

9

Puerto Ibanez

Pastoral

150

40

8

170 (?)

  

All had to be sold—now only 1.5 ha fertile

10

Puerto Ibanez

Mixed

200–250

40

7.5

80 (20)

   

11

Puerto Ibanez

Horticulture

1,000

40

1

 

  

Crops performed poorly for several years

12

Puerto Ibanez

Mixed

200

40

100

 

300 (260)

150 (150) Goats

40 sheep evacuated; Crops died

13

Chile Chico

Mixed

300–400

100

5

4

  

Crops abraded by wind-blown ash; cows all sold

14

Chile Chico

Mixed

300

100

5

 

30 (25)

 

Crops performed poorly for several years

15

Chile Chico

Mixed

300–500

100

350

 

400

 

All sheep sold

16

Chile Chico

Pastoral

200–250

100

>300

  

All evacuated by ferry to Puerto Ibanez—then sold

17

Chile Chico

Pastoral

450–500

100

520

100 (50)

400 (200)

2–3 horses

50 cow and 200 sheep evacuated and sold for 50% of original value

18

Los Antiguos

Horticulture

1,000(?)

80

4

   

Cherry trees abraded by ash—reduced production

19

Los Antiguos

Mixed

200

80

8

 

70 (70)

 

Crops performed better following ashfall

20

Los Antiguos

Horticulture

150–170

80

4

   

2 years of no production from the cherry trees

21

Los Antiguos

Mixed

200–250

80

70

 

30 (15)

 

In first two years, after eruption—fruit produced by very small

22

Perito Moreno

Mixed

400

20

  

370 (80)

  

23

Estancia

Pastoral

200–250

70

180,000

 

30,000 (15,000)

  

24

Los Antiguos

Pastoral

80

70

280

50 (1)

400 (60)

  

25

Cerro Castillo

Pastoral

600–1,000

n/a

100

5

60

  

26

Cerro Castillo

Pastoral

800–1,000

n/a

 

All died

All died

Horses died

 

27

Cerro Castillo

Pastoral

200

100

9

8

  

Cows all sold

28

Cerro Castillo

Pastoral

200–300

n/a

50

10–20

>50 (all)

 

All livestock evacuated and sold; moved farms following the eruption

29

Puerto Ibanez

Mixed

200

40

60

25 (0)

300 (20)

 

Evacuated survivors to Coihaique

30

Tres Cerros

Pastoral

40–50

40

20,000

 

12,000 (11,000)

  

31

Puerto San Julian

Pastoral

20–50

5

33,000

 

16,000 (?)

 

Most died

32

Rio Gallaous

Pastoral

30

0

60,000

 

15,000 (3,000)

  

Under livestock losses, numbers in brackets are the numbers of animals who died due to the eruption. Note that estimated ash thicknesses were given by interviewed farmers 17 years after the ash fall event

Agriculture is one of the main economic activities in the affected area and rural service towns are heavily dependent on the productivity of surrounding farms. Pastoral (livestock) farming for meat and wool production dominates the region. Farms in the upper Ibáñez valley, located in the southern Andes Mountains 20–50 km from Vulcan Hudson (Figs. 1, 3a, b), ranged from 50 to 200 ha (0.5–2 km2) in area, with semi-intensive combinations of sheep and beef cattle farming (approximately 0.1–1 livestock units per ha). In the lower Ibáñez valley, 50–90 km from Vulcan Hudson, including the settlement of Cerro Castillo, more intensive sheep and cattle farms occur (>1 livestock unit per ha; Fig. 3c). Warm, well-irrigated valleys draining into Lago General Carrera/Buenos Aries allow pockets of intensive, ground and tree crop horticultural farms and intensive pastoral farming (1–100 ha) on the outskirts of the rural service towns at Puerto Ibáñez, Chile Chico, Los Antiguos and Perito Moreno. In the vast steppe region from Perito Moreno to the Argentine Atlantic coast, large (>20,000 ha) low-intensity sheep farms dominate (Fig. 3d).
Fig. 3

a Fence buried by 1–1.5 m ash deposits in the upper Ibanez valley, ~45 km from Volcán Hudson. b Fields covered in primary and windblown ash in the Ibanez Valley, approximately 10 km west of Cerro Castillo. The farm has only recently been reoccupied. c Puerto Ibanez and surrounds illustrating intensive horticulture and pastoral agriculture. d Extensive pastoral farming at Tres Cerros. All photos were taken in January 2008

The climate in this region is typically dry, cool and windy. Rainfall decreases from >1,500 mm/year in the central southern Andes to 800–1,000 mm in lower eastern hill areas (Peri and Bloomberg 2002). The Andes acts as an orographic barrier to moist westerly winds resulting in a mean annual rainfall as low as 150 mm/year in the central steppe, increasing to 250 mm/year at the coast (Peri and Bloomberg 2002; Pasquini et al. 2005). Atmospheric precipitation is seasonal, with most precipitation in the Andean region recorded in winter (more than 70% occurs between April and September). In contrast, along the coastal zone most atmospheric precipitation occurs in autumn (March–May) and spring (September–November) (Pasquini et al. 2005). Potential evapo-transpiration ranges between 4 and 7 mm/day in summer, making irrigation essential for horticultural production (Peri and Bloomberg 2002). Temperatures are highest from December to February and at a minimum from June to July; summers are short, but with long days because of the high latitude. The maximum mean monthly temperature over 30 years at Perito Moreno is 20.4°C and minimum −3.0°C (Peri and Bloomberg 2002). The windiest season is from November until March (summer), with the predominant wind direction from the south-southwest quarter; severe and frequent windstorms occur in spring and summer, with wind speeds over 120 km/h at ground level.

3.1 Livestock impacts

The eruption occurred in August, at the end of winter, when pastoral farmers were already awaiting warmer spring growth conditions to replenish feed stocks and animals were in poor condition and particularly vulnerable to any stress (Wilson and Cole 2007). The winter of 1991 had been a particularly cold and stormy winter and most farms were overstocked, due to poor meat prices in the previous season. This had reduced available grazing and supplementary feed supplies across the Patagonian region (Rubin et al. 1994). Snowfalls of 20–40 cm also occurred in the Ibáñez valley in the weeks following the eruption, compounding existing problems of feed burial, roof loading and road access.

A significant animal welfare crisis rapidly developed following the eruption when the limited supplementary feed stocks were exhausted. Chilean government agricultural agencies Servicio Agrícola y Ganadero (SAG) and Instituto de Desarrollo Agropecuario (INDAP) attempted to organise and assist with evacuating livestock and sourcing further supplementary feed. Most farms in the Andean region and irrigated valleys lost up to 50% of livestock, and up to 90% were lost in the large steppe region (Table 2).

3.1.1 Gastro-intestinal impacts

Most livestock died of starvation when feed was covered in ash (Rubin et al. 1994). Where ash deposits were sufficiently thin to permit grazing, ash adhering to vegetation caused digestive problems; paradoxically, this hazard was often most severe further away from the erupting volcano (mirroring a pattern also seen in Iceland; Thorarinsson 1979). In some areas, hungry sheep grazed scrub and low trees coated with ash, whilst in others animals refused to graze and simply died of starvation. Veterinarian Don Julio Cerda Cordero of SAG worked with livestock in the Puerto Ibáñez area immediately after the eruption and reported ash ingested with feed accumulated in the rumen forming a “brick”, which blocked the gut, caused swelling of the intestines against the lungs and led animals to essentially die from asphyxiation. In contrast, Rubin et al. (1994) reported there was little ash ingestion or evidence of mechanical obstruction in the gut recorded during necropsies of sheep at Perito Moreno. Ewes aborted lambs due to high stress and malnutrition (Rubin et al. 1994; Inbar et al. 1995), but there were no confirmed instances of livestock being poisoned from ash ingestion in any studies, despite fears of high fluoride levels in ash samples from the first phase of the eruption (Banks and Ivan 1991; Rubin et al. 1994). Ash storms added to the problem ensuring that feed supplies were repeatedly covered in fine layers of ash remobilised by winds lengthening the time frame of impact (Black and Mack 1984; Wilson et al. 2010c).

3.1.2 Tooth abrasion

In all areas, but especially in the Argentine coastal steppe where ash was thinnest (≤50 mm), farmers reported that frontal grazing teeth were worn down almost to the gum, as animals tried to graze ash-covered feed. This was exacerbated by ash storms continually re-coating vegetation with fine ash. In extremely bad areas, sheep were crippled due to tooth damage within weeks of the ashfall. While some animals starved to death, surviving sheep suffered poor performance for the rest of their lives due to the worn teeth. By 2008, animals from the 1991–1995 generation had been replaced by new livestock.

3.1.3 Dehydration

Livestock suffered dehydration when fine ash repeatedly infilled and contaminated surface water supplies with high levels of turbidity in the Chile Chico, Los Antiguos and Argentine coastal steppe region. In addition to loss of primary water sources, constant abrasion dried out vegetation, another source of water for livestock. In Chile Chico and Los Antiguos, livestock were taken to Lago Gen. Carrera/Buenos Aries. However, in the steppe, shallow small lakes were turned into muddy swamps where livestock became stuck and often died. There were several reports of dead sheep lining the edges of such lakes, trapped within the ashy mud and sometimes piled 2–3 deep. Once ash deposits stabilised, after 5–6 years, the drinking water in small lakes rapidly cleared.

3.1.4 Immobilisation

Sheep in this area (Merino–Corriedale cross) have a fine-grade of wool which readily trapped large loads of fine ash. Apart from starvation and dehydration, many ewes were pregnant at the time of ashfall and some ended up carrying an extra load of up to 10 kg of ash. This ash load strongly impeded movement and caused many animals to collapse and eventually die. Some farmers removed wool from their surviving sheep to reduce the stress. The resulting fleeces from animals in Los Antiguos in 1991/92 weighed 10–12 kg, compared to a usual 3–4 kg. Shearing was difficult because the shearing-combs were rapidly abraded by the large quantities of ash in the sheep’s fleece. The livelihoods of shearers were destroyed along with that of farmers, following the major destocking of the region. Across the region, large volumes of stored wool were also contaminated when ash penetrated woolsheds, further compounding economic losses.

3.1.5 Blindness

Many sheep and cattle suffered permanent blindness due to abrasion of the cornea by sharp ash particles. Affected livestock reportedly walked in circles in Chile Chico, Perito Moreno and the steppe region following the eruption.

3.2 Vegetation and soil impacts

Heavy ashfall completely buried pastures (where vegetation consisted mostly of white and red clover and grasses) with >100 mm being sufficient to bury short winter pastures and inhibit its regeneration, ultimately resulting in farm abandonments (Fig. 3a, b). Ash was compacted by rain, animals and human activity, increasing the deposit bulk density by 50–100% (Cienfuegos and Beltrano 1995). In particular, the ash deposit developed a patchy, hardened surface or crust (Fowler and Lopushinsky 1986). This reduced water infiltration and inhibited vegetation from growing (Folsom 1986; Fowler and Lopushinsky 1986). Farmers reported that vegetation could penetrate ash deposits <70 mm thick, and in some cases, pastures were able to grow through desiccation cracks in ash 70–120 mm thick, particularly where there was no shortage of water. Small volumes of rain and irrigation water simply ran over the crust and a large volume of irrigation water was required to saturate the deposit unless cultivated, which mechanically mixes the soil and ash. This increased sediment run-off and sedimentation in irrigation canals.

In the upper Ibanez river valley, which received >2 m of ash, there were no operating farms in 2008. The soil mostly comprised of grains >2 mm in diameter with very little, fine organic matter, some lichen cover and scattered clover. Small endemic beech (Nothofagus) saplings were common (0.5–2.0 m in height), representing the first stage of ecological succession.

Farms with 1.0–2.0 m of ashfall have had sparsely vegetated pastures since 2000, and even by 2008, few areas can support livestock. White clover (Trifolium) was the first pasture species to return. Farms with 0.5–1.0 m ash have mostly re-established pastures since 2001, and support semi-intensive sheep and beef farming (~1 livestock unit per ha). Where there has been significant erosion and compaction of the ash to coverage of <200 mm, sufficient pasture (clover-dominated with some grasses) was present for intensive livestock farming in 2008.

An initial increase in vegetation growth following the ashfall was reported by many farmers in the Ibáñez valley, Chile Chico and Los Antiguos, which was attributed to a slight fertilising and mulching effect from the >50 mm ash deposits. Various studies indicated there were insufficient soluble elemental concentrations on the ash, however, to cause chemical toxicity in soils or plant (Banks and Ivan 1991; Rubin et al. 1994; Bitschene et al. 1993, 1995; Cienfuegos and Beltrano 1995; Inbar et al. 1995). Farmers interviewed in Puerto Ibáñez reported some pastures were yellowed and dehydrated, especially on the tips of grass leaves, characteristic of acid damage (Grattan and Pyatt 1993; Dale et al. 2005). The ash acted as a lithic mulch, increasing soil–water retention and slowing evaporation, similar to that observed at Sunset Crater, Arizona, USA, and at Vulcan Parícutin (Mexico) (Rees 1979; Cienfuegos and Beltrano 1995; Bitschene et al. 1995; Ort et al. 2008). This did not occur in distal areas (steppe) due to rapid stripping of the ash deposits by winds (Bitschene et al. 1995).

Once pasture was buried by ashfall (generally >50 mm), pastoral farming recovery was dependent on a successful spring growth period. Farmers in the irrigated valleys reported pastures and alfalfa hay were growing again by December 1991, but suffered damage from later ash storms which reduced pasture and supplementary feed stocks (e.g. hay) for the following winter. Supplementary feed (alfalfa hay) production in Perito Moreno decreased by about 30% for 2–3 years after the ashfall before returning to pre-eruption levels.

Eruption timing was fortunate for horticultural farming located in an irrigated valley surrounding Lago General Carrera/Buenos Aries. Most crops had not yet been planted or were in dormancy in early August (winter). Low crops would have been smothered and tall crops would have experienced reduced photosynthesis and possible acid burns from resulting ash cover. However, the windblown ash caused significant problems over the crucial spring growth period (October–November) in 1991 and during subsequent harvests for 2–5 years (Inbar et al. 1995). The abrasive suspended and saltating ash particles ‘ash-blasted’ exposed vegetation, soils and livestock. In particular, cherry fruit trees in Los Antiguos were badly affected through abrasion to buds and blossoms (Inbar et al. 1995). Tomato and alfalfa hay crops were also sensitive to abrasion by wind-blown ash, while root crops such as potato and garlic were most resilient. Horticultural farmers typically had the capacity (equipment and financial reserves) to mechanically cultivate the ash into the soil. They also had access to irrigation water, which was a significant advantage to promote vegetation recovery and to aid the integration of the ash into the soil.

For several years following the eruption, water and wind eroded ash from agricultural land, encouraging vegetation recovery, particularly in the Ibáñez valley and surrounding Lago Buenos Aires. However, once exposed, the pre-existing soil suffered increased erosion by high-energy saltating particles.

3.2.1 Effect on soil fertility

The trachyandesitic Hudson tephra was rich in potassium (2–3 wt% K2O), phosphorous (0.4–0.8 wt% P2O5) and sulphur (0.1–0.2 wt% S) (Banks and Ivan 1991; Bitschene et al. 1993, 1995; Scasso et al. 1994). However, these elements were mostly locked within crystals and glasses and not available for immediate extraction from soils by plants (Table 3).
Table 3

Analyses of extractable elements from the 1991 Hudson tephra (CAL-first extraction method with total ash sample)

Extractable element

Bregliani et al. (1993) (mg kg−1)

P2O5

10

K2O

7

MgO

60

CaO

200

S

100

Soil sampling (Fig. 2) was undertaken along the longitudinal axis of the fallout deposit. Results are given in Table 4. Soil samples were air-dried and sieved (<2 mm) before being analysed for extractable sulphate following the method of Blakemore et al. (1987). Total soil nitrogen and carbon was determined by Kjeldahl wet digestion (Parkinson and Allen 1975) followed by automated analysis. Soil pH was measured using a glass electrode pH meter with a soil/water ratio of 1:2.5 (w/v) (Blakemore et al. 1987). Exchangeable cations were determined by 1 M neutral ammonium acetate extraction. Olsen-extractable soil phosphorous was determined by shaking 1 g air-dried soil samples with 20 ml of 0.5 M NaCO3 solution (pH 8.5) for 30 min (Olsen et al. 1954).
Table 4

Soil fertility analyses from soils collected from ash fall out area during fieldwork in January and February 2008 (locations shown on Figs. 1, 2)

ID no.

pH

Olsen P (μgP/g)

SO4 (μgP/g)

K (me/100 g)

Ca (me/100 g)

Mg (me/100 g)

Na (me/100 g)

C (%)

N (%)

CEC (me/100 g)

Bulk Density (g/ml)

% >2 mm

KM from vent

Description

5.6–6.5

20–80

10–20

0.5–1.0

6–12

1–3

0–0.5

10–20

0.5–1.0

25–40

Recommended levels for healthy pasture growth in this region

H1

5.6

3.2

48

0.38

3.6

0.73

0.12

15.35

0.95

26

0.61

2.5

19

Paleosol

H2

6.1

8.3

2

0.08

0.6

0.08

0.05

0.42

0.04

6

0.54

47.8

19

Ash/topsoil

H4

6.2

3.6

4

0.09

0.6

0.06

0.09

0.22

0.01

25

0.54

54.5

20

Paleosol

H5

5.6

10.9

5

0.28

3.7

0.43

0.16

3.46

0.14

8

0.61

40.4

20

Ash/topsoil

H7

5.8

4.1

18

0.08

0.3

0.06

0.07

0.07

<0.01

2

0.75

41.2

29

Ash—wind reworked

H8

6.2

6.7

16

0.12

7.9

0.82

0.16

3.52

0.27

14

0.82

3.2

35

Paleosol

H9

5.6

20.2

32

0.14

16.0

0.88

0.24

11.36

0.78

32

0.65

2.3

35

Paleosol

H10

5.9

3.1

11

0.07

0.3

0.06

0.09

0.06

<0.01

2

0.91

35.0

35

Ash/topsoil

H11

5.9

3.3

10

0.10

0.2

0.04

0.10

0.07

0.01

2

1.10

11.1

35

Ash/topsoil

H15

5.8

3.8

70

0.10

1.8

0.16

0.19

4.16

0.27

10

0.82

3.1

48

Paleosol

H17

5.2

13.4

10

0.28

1.8

0.39

0.23

2.85

0.23

6

0.80

19.5

48

Ash/topsoil

H19

5.6

31.8

4

0.38

17.7

2.27

0.11

5.07

0.27

28

0.79

0.0

65

Paleosol

H20

5.9

24.0

15

1.32

7.8

1.60

0.19

3.60

0.29

15

0.87

7.8

65

Ash/topsoil

H21

5.8

25.4

5

0.54

7.6

1.69

0.06

2.68

0.20

14

0.86

0.0

65

Paleosol

H22

5.8

22.6

6

0.42

3.5

0.53

0.12

1.43

0.11

6

0.93

15.2

65

Ash/topsoil—cultivated

H23

6.0

13.6

6

1.18

9.4

2.53

0.10

4.43

0.39

16

0.80

1.8

70

Topsoil

H24

6.6

3.3

2.5

0.13

0.8

0.22

0.07

0.08

<0.01

3

1.18

0.0

90

Ash—wind reworked

H25

7.0

5.5

7.8

0.33

12.6

2.32

0.21

0.86

0.08

15

0.93

5.0

98

Topsoil

H26

7.0

16.6

4.0

1.74

20.7

3.52

0.10

4.17

0.37

26

1.03

6.0

98

Topsoil—cultivated

H27

7.0

4.2

1.0

0.51

23.4

5.38

0.18

2.82

0.26

29

0.99

15.0

98

Paleosol

H28

6.6

10.9

38.8

0.62

22.4

10.80

0.35

2.37

0.19

35

1.02

0.0

100

Topsoil—cultivated

H29

8.0

18.8

49.5

2.52

90.1

11.24

1.84

2.89

0.22

n/a

1.06

3.6

145

Topsoil—cultivated

H30

6.9

11.8

5.0

1.47

18.8

5.41

0.15

2.76

0.22

26

1.05

0.4

120

Topsoil—cultivated

H31

8.0

3.9

1.3

0.74

25.7

3.55

0.22

0.80

0.06

n/a

1.19

0.0

121

Topsoil

The lack of baseline data on pre-eruption soils prohibits comparative analysis; however, the data give some insight into soil fertility variations in different locations and the relative success of different mitigation techniques. Samples taken in the upper Ibáñez valley generally showed extremely poor soil fertility. Cation exchange capacity (CEC) was particularly low, highlighting the lack of clay minerals and soil organic matter to hold nutrient cations in top soils. Other key elements, such as P and N were also very low. Increases in pH and CEC with distance from the vent (due to increasing K, Ca, Mg and Na) appear to be due to increasing aridity eastward. Paleosols in general had better physical fertility characteristics with higher CEC and bulk densities when compared with top soils, due to their finer grain size and higher clay content. However, their chemical fertilities were generally poorer than top soils, which typically had higher carbon and nitrogen contents, reflecting current plant growth. Phosphorous was generally low and variable, but was typically higher in top soils. The bulk density of top soils also generally increases with distance from the vent, reflecting both decreasing grain size and volume of pyroclastic products within the soil away from the vent. The greatest total soil fertility was achieved where ash and paleosol were mixed, providing chemical (higher CEC and P, C and N contents, probably reflecting greater organic matter content in the soil) along with increased aeration and moisture-holding capacity (Fig. 4) (Ugolini and Zasoski 1979; Shoji et al. 1993; Ort et al. 2008). Most farmers who cultivated ash into their soil considered the practice to help grass and horticultural ground crops re-establish within 1–3 years or sooner.
Fig. 4

Selected soil fertility indicators of top soils along the axis of the 1991 Hudson fall deposit (as shown in Fig. 1). Samples from cultivated soils are denoted by an arrow. CEC = Cation exchange capacity (in me/100 g); Olsen P = Olsen-extractable soil phosphorus in μgP/g (using method of Olsen et al. 1954); Mg (in me/100 g); Ashfall thickness from Scasso et al. (1994)

3.2.2 Effects on water retention

Coarse grained (>1 mm) surface soils form a porous blanket that helps retain soil moisture in underlying soils for longer periods. Cienfuegos and Beltrano (1995) reported that following the ashfall this process led to reactivation of plant cover and facilitated the growth of small plants. This had also been observed by Colton (1965), Waring (2007) at Sunset Cater, Arizona, United States. Pure ash from Los Antiguos was found to have 35.1% water retention potential, whilst a 50:50 ash and clayey-soil mix gave 62.2% (Bitschene et al. 1995). Where ash was cultivated into soil, there was greater water retention than in uncultivated ash deposits, but still lower than pre-ashfall levels, leading to increased irrigation requirements.

3.3 Water supplies

Settlement patterns in the region are closely related to water access. Pockets of intensive agriculture and horticulture have developed with irrigation in areas at Puerto Ibáñez, Chile Chico, Los Antiguos and Perito Moreno. In general, surface waters are used for irrigation, and groundwaters and spring-fed supplies are used for municipal supply (except at Puerto Ibáñez). In the upper Ibáñez valley, spring-fed water supplies remained relatively clear, even after heavy ashfalls and throughout the period of wind-blown ash. The Puerto Ibáñez drinking and irrigation water supply is fed via an open channel from natural springs in hills north of the town. This supply developed high turbidity following the 1991 ash fall, and for periods of several days following subsequent ash storms up until 1994–1995. This deterred people and livestock from drinking the water. No chemical metallic taste was noticed, suggesting there was little leaching of metallic salts from the ash (Stewart et al. 2006). Sedimentation of ash and reworked ash in farm surface water supplies (open river intakes and a ditch irrigation network) occurred following the ashfall and ash storms, which blocked irrigation channels in many places. Blocked ditches required ongoing, time-consuming cleaning operations for 2–3 years in Puerto Ibáñez, Chile Chico and Los Antiguos. Some abrasion damage also occurred to metal fittings in irrigation systems (Wilson et al. 2010a).

3.4 Psycho-social trauma

Several interviewed farmers emphasised the high mental stress and severe economic, physical and emotional hardships following the ashfall. These were driven by the physical impacts on livestock, the extended and repeated periods of darkness during ash storms, the transformation to a dull and grey ash-covered landscape, chronic water supply issues, household contamination by ash, fears for health and livelihood, and lack of awareness of and control over events. Some people were driven from the region. One farmer reported her husband “went into a depression that he never really got out of”.

The community at Puerto Ibáñez, in both town and its surrounds, lost 30% of its 4,000 inhabitants to other regions following the 1991 eruption. This was not from widespread farm abandonment following the ashfall, as within the upper Ibáñez valley and the Argentine steppe, rather it reflected a slower decline. Farmers attempted to continue farming, but after several years of failed crops, slow recovery of soil fertility and selling off livestock to raise income, many had to sell their land at very low prices and relocate. Remaining farmers adopted a risk-averse approach to farming where possible, keeping stock levels to an absolute minimum and increasing savings (Oscar Albornoz, Puerto IBanez Municipal Secretary, pers comm. 2008). For those who could not sustain an income from farming, one of the greatest challenges was trying to find alternative employment in the region. The municipality attempted to offer courses and workshops for struggling farmers, but there was extremely low participation (O. Albornoz pers comm. 2008).

4 Farm abandonments

Widespread farm abandonments (of >3 year) occurred in two areas with different climate, agricultural practices, and which received very different ashfall thicknesses; the upper Ibáñez valley west of Puerto Ibáñez (800 to >2,000 mm ash), and the steppe region of extensive pastoral ranch style farming (<75 mm ash). Most farmers initially believed they would only need to evacuate their farms for days to weeks. But once their resource and employment base was destroyed, they were forced from their lands. There was either no resale market for the farms or prices were significantly below pre-eruption value and farmers were not prepared to accept them. This ruined the financial equity of farming families, and because most only knew this livelihood, they had few other employment prospects. Many also said they had hoped to return in the short term, citing strong family ties and emotional attachment to the area. In general, elderly farmers were more likely to evacuate their farms and were less likely to return, citing they did not have the physical or emotional energy to try to recover from the eruption event. The impact of the loss of financial equity was highest for elderly farmers, who either expected to retire on their land or use the money from the sale of their farm to support their retirement. Others reported not having the financial capacity to bring farms back into production, despite available credit assistance. This was particularly the case on the steppe. Three farmers at Tres Cerros (1) and Puerto San Julian (2) maintained significant other business interests to provide financial security, although the business at Tres Cerros had been established prior to the eruption.

By 2008, many abandoned farms in the Ibáñez valley had been re-occupied, with the exception of areas with >2 m of ash. The key determinant was vegetation recovery. In the ecologically and climatically similar Ibáñez valley and irrigated regions surrounding Lago Gen. Carrera/Buenos Aires, increasing ashfall thickness led to longer abandonment (approximately 1 year of abandonment per 60 mm of ashfall) (Fig. 5). In the Ibáñez valley, many farms close to Cerro Castillo (100–300 mm ashfall) were reoccupied within 1–5 years. Farther up the Ibáñez valley, the duration of farm abandonments directly increased with ash thicknesses (Fig. 5). In the central part of the ash fall deposit in the upper Ibáñez valley with >1 m ash, some farmers only returned after 13–15 years. Even so, very limited farming was occurring as late as 2008 despite re-habitation. Areas with greater than 1.5 m ashfall did not support any farming in 2008. Some farms diversified and changed land-use practises. In the upper Ibáñez valley with >1 m of ash, farmers mostly now rely on lumber and fire wood extraction as the new source of income. Some farms were planted in exotic pine forest after the eruption. Further details of farm abandonments and evacuations as a result of this eruption are given in Wilson et al. (2010b).
Fig. 5

Time till farm reoccupation following the 1991 Hudson eruption. X axis = year of return to farm; Y axis = thickness

5 Managing agricultural recovery

Farms that were not abandoned in the ashfall zone used a variety of agricultural, economic and social recovery strategies.

5.1 Livestock evacuation

Fear of health impacts on livestock, livestock feed availability, slow pasture recovery and the threat of future eruptions motivated the evacuation of thousands of livestock (particularly cattle) in the Ibanez valley and from Chile Chico, Los Antiguos and Perito Moreno (Wilson 2009). In addition to animal welfare considerations, livestock evacuations attempted to protect farmer capital. However, the cost of evacuating livestock was beyond the means of most farmers and no one had livestock insurance. Evacuated animals could not be quickly returned to their home farms because feed was buried under ash, supplementary feed exhausted and insufficient additional feed was transported into the area. There was also insufficient grazing land available in refuge areas and it was expensive to rent. Most farmers were forced to sell their animals for low prices due to their poor condition and a market glut (Don Julio Cerda Cordero, SAG Veterinarian pers comm. 2008). This loss of equity greatly reduced the ability of farming families to recover from the effects of the ash fall, having to wait till their farms could sustain livestock again and they could raise the capital to buy new livestock (which had returned to normal prices). Traders came from outside the region to take advantage of the cheap livestock and in some cases cheap land. In one instance, a trader used a false account to buy cheap livestock and land from desperate farmers, using false cheques to pay. Whilst this individual was prosecuted, such experiences caused even further distress for affected farmers (Don Julio Cerda Cordero pers comm. 2008).

5.2 Rehabilitation of soils

The rehabilitation of soil to produce pasture and crops was a priority. Physical fertility may be maintained for 10 s to even 100 s of years following burial under ash deposits if the soil maintains a low bulk density and moderate contents of organic matter and clay minerals for cation exchange (Shoji et al. 1993). Chemical fertility, however, is often lost over time after ash burial, as highly soluble elements such as nitrogen, organic carbon and sulphur, leach out. Given sufficient time, uncovered soil can be restored with vegetation and fertilisation more readily than trying to develop a new physical medium from the new ash deposits (Wilson 2009). Natural soil recovery can occur by erosion of unconsolidated ash exposing the buried soil. Surviving vegetation (such as deep rooted trees) may also provide organic matter for new soil formation (Ort et al. 2008). In a moist environment, this may take several decades and in a semi-arid environment up to 1000 years (Rees 1979; Bocco et al. 2005; Ort et al. 2008). Such time frames are unacceptable for farmers willing to remain working the land. At Parícutin, Mexico, the best way to rehabilitate arable land was to cultivate tephra into the buried soil beneath (Rees 1979; Luhr and Simkin 1993; Ort et al. 2008). Similarly, Chilean and Argentinean farmers tried cultivation and often returned to growing crops, which also stabilised the ash deposits. The techniques used depended on the type and intensity of farming; access to resources, credit and irrigation.

Upper Ibáñez valley farmers in areas of heavy ashfall (>0.5 m) had some success spreading different varieties of grasses on the ash/soil, including indigenous and foreign ryegrasses and red and white clovers. Hay was spread on the ash to increase organic content and provide an organic mulch. It proved too expensive and the ash too thick to cultivate it into the buried soil. Application of fertiliser was ineffective due to its rapid leaching out of the ash after application due to the coarse grain size of the ash. Vegetation recovery was highly dependent on soil moisture retention, with depressions and irrigated areas recovering most rapidly.

Intensive pastoral and horticultural farmers at Chile Chico, Los Antiguos and Perito Moreno found ash cover >50 mm halted agricultural production and required immediate treatment. Tractor mounted-ploughs (chisel and furrow ploughs) or tractor mounted-rotary hoes were used to mix the ash into the soil. Regular mixing with hand hoes and spades was required for several years afterwards. Cultivation with deep harrows (tine ploughs) was effective for <70 mm deposits whilst furrow and disk ploughs were most effective for ash up to 150 mm, but could be used on uncompacted ash up to 250 mm. In topographical depressions and where ash deposits had been over-thickened by reworking up to 400 mm, ploughs could not penetrate. In such cases, farmers waited for the wind to erode the ash cover. Some farmers used rakes and shovels to mix the ash into the ground to beneficial effect, achieving greater yields after 2–3 years (Valdivia 1993). Some farmers in Chile Chico dug out buried alfalfa crops and topsoil in an unsuccessful attempt to save the crop, and then resorted to burying the ash beneath. It took 2–3 years for new alfalfa to grow back, despite continual planting. Horticultural production began again within 3–24 months and pastoral farmers reported adequate pasture cover within 3–48 months; a faster recovery than in Puerto Ibáñez despite thicker ashfall. Hard ash crusts required several passes of chisel or furrow ploughs to break it up. Some farmers saturated the ash with irrigation water, which eventually allowed water to percolate through to the soil beneath in an attempt to initiate growth of buried crops. One farmer unsuccessfully tried to flood his paddocks to break up the hard cap and wash it away. Following several crop rotations, coarser lapilli now accumulates on the soil surface, requiring additional deep ploughing and mixing. Horticulturalists who intensively cultivated soils reported increased yields within 1–5 years.

Intensive pastoral and horticultural farmers in Puerto Ibáñez did not generally cultivate their land due to the cost. Crops and pastures took up to 10 years to fully re-establish. In some instances, land had to be retired or changed from cropping to pasture production due to the poor soil growth response. Pastoral farmers in these areas reduced livestock numbers and relied on trees to supplement poor pasture growth. Uniquely in Puerto Ibáñez, a grader was used to strip/grade 100–150 mm ash deposits off some farms close to the township 1–2 weeks after the ashfall. The ash was collected and dumped as an extension of the municipal road and town cleaning programme. In these areas, crop and pasture recovery was rapid, often reaching levels expected only during normal spring growth. Rehabilitation methods were complicated by ash storms which damaged recovering vegetation, particularly during an intense period of high winds 3–4 months following the eruption, and each spring for 3–10 years afterwards (Wilson et al. 2010c).

The success of pasture re-establishment across the study area is summarised in Table 5, with data from farmer interviews and field mapping allowing a comparison between pasture recovery time across the region, and different ashfall thicknesses and rehabilitation techniques. Regions with similar climates, soil conditions and land-use intensities and activities selected. Note that the steppe has not been included because a long period of windblown ash (ash storms) hindered pasture recovery (Wilson et al. 2010c).
Table 5

Summary of pasture re-establishment in the Ibanez valley and irrigated valleys

Unconsolidated ash thickness (mm)a

Compacted ash thickness (mm)b

Pasture recovery (years)c

Unassisted

Assisted

Treatment

Ibanez valley

<50

<30

0.1–0.5

No data

50–150

30–80

1–2

No data

150–300

80–150

1–5

No data

300–500

150–350

2–8

1–5

Stripped ash; seeds spread

500–1,000

200–700

8–>17

5–8

Hay put down; seeds spread

>1,000

>1,000

12–>17

10–>17

Spread seeds and fertiliser

Irrigated valleys

<20

<10

0.01–0.1

0.01

Spades; hoes; irrigation

20–50

10–30

0.1–2

0.01–0.1

Cultivation; irrigation

50–100

20–70

0.3–5

0.1–2

Cultivation; stripped ash

100–300

50–100

0.5–5

0.1–3

Cultivation

>300

100–150

2–10

 

Waited for erosion

‘Unassisted’ relates to pastures which have had no human intervention to assist pasture recovery. ‘Assisted’ is where cultivation, fertilizer, irrigation or seeding improvements have been undertaken to hasten pasture recovery

aFarmer estimate of ash thickness (interviewed in 2008)

bMeasured in field in 2008 and compared well with isopach map by Naranjo et al. (1993) and Scasso et al. (1994)

cSufficient to sustain pastoral agriculture

5.3 Uncertainty

During the emergency response and recovery from the 1991 eruption of Vulcan Hudson, farmer’s uncertainty of the human health impacts motivated many to evacuate. In the longer term, significant uncertainty also surrounded the length of time vegetation production and soil resources would take to recover. In hindsight, some farmers in Chile Chico said that they would not have sold their livestock, because now they know that grass can grow back even with 30–50 mm ash. The confusion and uncertainty at the time, coupled with the poor condition of livestock, led them to sell. The severe ongoing impacts from ash storms which acted to suppress local and regional agricultural recovery were an unexpected and complicating factor for recovery.

5.4 Irrigation access

Access to irrigation water was initially an important vulnerability for high-intensity farmers, with irrigation canals blocked by heavy sedimentation following the ashfall (Wilson et al. 2010a). After 1–3 years of restoration, irrigation could again satisfy the water demands of young plants even with the lower water-holding capacities of the new soils (Wilson et al. 2010a, b). Farms without irrigation took significantly longer to recover; at Perito Moreno, for example irrigated pastures could sustain livestock within 3 years, compared to >5 years for pastures not irrigated (Shaquib Hamer pers comm. 2008).

5.5 Government assistance and livelihood changes

Government agencies played an important role in the agricultural response and recovery from the ashfall. In all impacted areas, Chilean and Argentine government agricultural agencies, civil defence and military staff were deployed to the region to assess the impacts and the aid required, ensure basic needs were met, and assist in the recovery process. Interviews with emergency management staff indicated the emergency response was hindered by the lack of a clear emergency response plan. A number of government agencies in the region attempted to respond with little co-ordination. Over the first 4–8 weeks, assistance centred on providing evacuation coordination for people and animals and providing supplementary livestock feed. In Chile, government agencies assisted through into the recovery phase by providing credit (e.g. for cultivation of ash) and advice for farmers on post-ashfall adaptive strategies. These included the use of appropriate seeds, soil management, use of plastic sheeting to protect against wind erosion, and diversification of production through the introduction of green houses (for horticulture). There were no direct measures to assist farmers resettle elsewhere and apparently little assistance from central government for those who did not own land (i.e. social welfare).

No resale market existed for farms devastated by thick ash deposits; therefore, the Ministry of Public Works (manages Chilean government land) offered to purchase abandoned farms within 60 km radius of the volcano. The payment was significantly less than the pre-eruption value, but provided farmers with the means to relocate and pursue other employment opportunities. Original farmers were given the first right of re-purchase, which successfully catered for the strong emotional attachment farmers had with the land. Some farmers have used this clause to return.

There was significant farmer use of credit assistance in Chile. However, there was relatively poor participation at agricultural extension workshops. Agricultural officers and municipal officials commented that the scale of the disaster seemed to have overwhelmed some farmers, resulting in a dependence mentality where farmers expected the government to pay for all restorative actions (Oscar Albornoz pers comm. 2008). The former Governor at Chile Chico, Sn. Juan Mercegui (pers comm. 2008), said farmers were angry that the government did not hand out aid (material goods or money). Yet, when potato and grass seed were distributed to farmers, it was mostly sold off. Only a small minority of motivated Chilean farmers took advantage of the aid programmes offered and used the techniques to farm their way out of the situation. As a consequence, there has been limited change in farming techniques following the eruption, beyond the widespread and successful adoption of greenhouse cultivation in the lower Ibáñez valley. Farmers simply reduced their stock rate or horticultural production. Seed varieties suitable for growing in ashy soils were not adopted. The prohibitive cost of plastic sheeting meant this was not widely used, despite its apparent success at mitigating erosion during ash storms. Some farmers in the lower Ibáñez valley have now diversified into tourism, opening camping grounds and home-stays.

In contrast, Argentine farmers who attended agricultural extension workshops in Perito Moreno and Los Antiguos described the programmes as excellent. There was also widespread use of credit assistance. Crop failures and dramatic drops in livestock and wool production led Argentina to provide direct aid grants to affected farmers. By comparing government records of farm productivity before and after the ashfall, the level of impact was calculated and the subsidy assessed accordingly. Most farmers in Perito Moreno reportedly took advantage of the government subsidy to buy more livestock, while others used it to relocate from the area.

The ashfall created some unexpected opportunities for agriculture. A key government aid measure for the Chile Chico area was restoration and expansion of the irrigation system. Inspired by the relative success of the Los Antiguos irrigation system, the scheme has greatly aided recovery in the area and stimulated significant additional agricultural opportunities and intensification by providing reliable and relatively secure water access for livestock and horticultural farming practices.

6 Productivity changes

Interviewed farmers were asked to estimate the change in farm productivity between the 1991 eruption and 2008 (Fig. 6; Table 2). Production from farms with >300 mm ash in the Ibáñez valley decreases with increasing ash thickness, similar to the trend in farm abandonments (Fig. 5). Farms with <300 mm of ashfall show productivity changes linked to availability of other factors such as irrigation and soil mixing. Farmers undertaking intensive farming in the irrigated valleys had access to, and made greater use of resources and technology which allowed them to recover better. Mechanical mixing of ash into soil was possible on the smaller fields, but could not occur in the larger, less intensively farmed upper Ibáñez Valley and steppe regions. Greater access to graders, tractors, ploughs, and established improvements such as wind breaks, did much to mitigate the effects of the ashfall and ash storms. The more productive horticultural farms were able to apply fertiliser and cultivation treatments enabling them to recover successfully. An important distinction is that whilst many intensive horticultural farmers evacuated for months to years during the ash storms period, few abandoned their farms in the long term, while many pastoral ranch style farmers did so. This is largely because their farms were already marginal and the eruption made them uneconomic for the reasons given below (Wilson et al. 2010b).
Fig. 6

Farmer perception of productivity change following the 1991 eruption of Vulcan Hudson. X axis = year of return to farm; Y axis = thickness. Positive values reflect farmer perception of improved economic performance of the farm; negative values reflect decreased economic performance

The two farms on the Argentine coastal steppe (Fig. 6) had only recently been re-inhabited and maintain other commercial interests to remain economically viable. The steppe region was agriculturally in decline prior to the 1991 eruption due to several years of drought and a harsh winter compounding the feed crisis. Farmers were also constrained by an overall poor economic situation due to low commodity prices and had low cash reserves and high livestock numbers retained in the hope of improved future prices. The area also had a dominantly mono-commodity (sheep) farming system from which was near impossible to diversify, due to poor soil fertility and the arid climate. Steppe farmers thus required greater financial capital to successfully return to farming, as they needed to purchase a large number of livestock to profitably farm in the region. The ash fall and ongoing impacts of the ash storms, ultimately accelerated many farmers to abandon their previous farming practises.

7 Summary

The 1991 Hudson ashfall and subsequent reworking of the ash during ash storms contributed to significant and prolonged impacts and recovery challenges for agriculture in Chile and Argentina. Although the eruption lasted only 4 days, the volume of tephra erupted was significant (4.3 km3 bulk volume). Lessons from the eruption are therefore invaluable for the mitigation of future large eruptions. Volcanological factors were important controls on the initial impact, such as thickness of ash, grain size, and soluble salt content as well as the timing of the eruption with respect to seasons and the agricultural cycle. The lack of significant concentrations of toxic soluble salts on the ash made physical impacts vastly more damaging than chemical impacts. This differs from smaller mafic eruptions such as those at Ruapehu or Hekla where the opposite occurred (Thorarinsson 1979; Cronin et al. 1998). Confusion around this issue highlights the value of rapid ash analysis to inform emergency response and recovery.

Pastoral farmers were impacted by ashfall burial of vegetation, which was remobilised by wind, further suppressing the recovery of vegetation. Starving livestock were dependent on supplementary feed, which if unavailable necessitated a reduction of stock, through evacuation, forced sale or death. Livestock also suffered physical impacts from the ashfall. Poor livestock health and saturation of the market resulted in lower livestock sales and consequently a major reduction in farm equity. The lack of reliable records of Chilean livestock populations severely inhibited evacuation and feeding efforts, and the very poor condition of livestock often made evacuation uneconomic. Also the lack of capacity within the local livestock market and lack of available alternative grazing to deal were important contributors to economic hardship in the region. Restocking depended on availability of feed supplies (vegetation recovery) and access to sufficient credit. Long-term farm abandonment occurred in areas of heavy ashfall (upper Ibáñez valley) and in areas of highly stressed farming systems (in the steppe).

The impacts of ashfall on mixed (pastoral and horticultural) and horticultural farms were initially less important, since the eruption occurred in winter and annual crops were not planted. Farmers also typically had the equipment and necessary resources to cultivate the ash into the soil.

Where the thickness of the ash was not overwhelming, a variety of agricultural, economic and social strategies were used in emergency response and recovery, but it was ultimately the overall economic and social ‘health’ of the farming system that determined the level of recovery (Lyons 1986). Thus, the amount of damage did not decrease linearly with distance from the volcano, rather, farms hundreds of kilometres from the volcano that were already under stress, failed, whilst closer farms with comparatively heavy ashfall, returned to agricultural production.

Previous studies have suggested volcanic disasters may act as catalysts accelerating the rate at which adjustments in ongoing economic and social systems occur. Community resilience is largely dependent on pre-existing social, economic and political conditions as well as post-disaster responses, relief efforts, mitigation strategies and longer-term rehabilitation programmes (Boyce 2000; Tobin and Whiteford 2002). The mono-agricultural system of sheep farming in the steppe region proved less resilient than the diverse horticultural and pastoral mix in the irrigated valleys, which allowed more rapid adaption through diversification (Reycraft and Bawden 2000). Natural advantages and greater investment in capital improvements led to greater initial damage potential, but ultimately provided greater capacity for response and recovery. So, better soils, climate and significantly greater access to technological improvements (e.g. cultivation tools, irrigation and wind breaks), such as occurred at Chile Chico, Los Antiguos and Perito Moreno, were advantageous. Cultivation increased chemical and physical soil fertility, especially when used in combination with fertilisation and irrigation. Appropriate use of seeds and cropping techniques within the new soil and growing conditions were also important, as was access to water.

Government agencies played a vital role in the dissemination of key information on appropriate farm management responses, carry out ash chemistry analyses, facilitate evacuations, and provide technical and credit assistance to facilitate long-term recovery. The large geographical extent of the impacted area was a barrier for emergency response, and resulted in isolation of some communities. Initially, Chilean and Argentine agricultural agencies coordinated livestock evacuation and emergency feed, and in the longer term provided advice on soil and farm rehabilitation strategies, provided machinery and supplies for rehabilitation strategies, and perhaps most importantly, provided credit assistance. In extreme cases, the Chilean government purchased heavily impacted farms, but gave farmers a first right of re-purchase, allowing farmers the opportunity to relocate but maintain ties with their land. This engagement with farmers was important, promoting agricultural education and assistance programmes. Where used these programmes empowered farmers to make appropriate farm management decisions, avoiding adopting a fatalistic dependence mentality. A significant issue for government aid managers was whether previous farming practices would be viable after heavy ashfall and whether further investment was worthwhile. Government aid had to be carefully considered to empower farmers to recover as efficiently as possible, but avoid subsidising unsustainable farming practises.

Ultimately, the success of recovery was determined by the farmer. Adoption of mitigation and adaption measures required a complex trade-off between yield expectations, projected costs, available physical/technical practises and, most importantly, the physical, intellectual and emotional capacity of the farmer. The ability of the farmer to adapt was vital. Similarly, the farmer’s commitment to rebuild the farm, participate in aid programmes, and be decisive about the future was the key to long-term recovery.

That many farmers returned, citing strong emotional attachment to the land, suggests that psychosocial drivers may outweigh economic drivers in some cases. Further studies following volcanic eruptions should consider the long-term implications of this observation and analyse whether economic, social or other drivers.

Notes

Acknowledgments

The authors would like to thank David Dewar for his outstanding translation and field support. We thank and acknowledge funding assistance from the New Zealand Ministry of Agriculture and Forestry Grant POR/SUS 7802/40 (Wilson), Earthquake Commission, Foundation of Research Science and Technology Grants MAUX0401 (Cronin) & C05X0804 (Johnston & Cole), and the University of Canterbury Mason Trust. Thank you to Bob Tose, Ian Furkert, Lance Currie and Ross Wallace for soil analyses. Thank you to Tina Neal and an anonymous reviewer for insightful and very supportive reviews. Sincere thanks to interviewees—in particular: Don Julio Cerda Cordero, Veterinarian, SAG; Uylsies Pededa, farmer & artist, Puerto Ibanez; Ananias Jonnutz—Productov, Orchardist, Los Antiguos; Don Hector Sandin, Ranch owner, Los Antiguos/Perito Moreno; Luis Fernando Sandoval Figueroa, Civil Defence Officer, Los Antiguos; Shaquid Hamer, former Agricultural Officer for El Instituto Nacional de Tecnología Agropecuaria, Argentina (retired), Perito Moreno; Don Hugo Ciselli, mechanic & farmer at Tres Cerros; Antonio Tomasso, cable television installation specialist & farmer, Puerto San Julian; Alberto James Alder, former Mayor, Puerto San Julian.

References

  1. Annen C, Wagner J (2003) The impact of volcanic eruptions during the 1990s. Nat Hazards Rev 4(4):169–175CrossRefGoogle Scholar
  2. Banks NG, Ivan M (1991) United Nations mission to Volcán Hudson, Chile, 20 August to 15 September 1991. Report, US Geol Surv, Cascade Volcano Observatory, 161 pGoogle Scholar
  3. Bitschene PR, Fernandez MI (1995) Volcanology and petrology of fallout ashes from the August 1991 eruption of the Hudson Volcano (Patagonian Andes). In: Bitschene PR, Menida J (eds) The August 1991 eruption of the Hudson Volcano (Patagonian Andes): a thousand days after. Cuvillier Verlag, Gottingen, pp 27–53Google Scholar
  4. Bitschene PR, Mendia J (eds) (1995) The August 1991 eruption of the Hudson Volcano (Patagonian Andes): a thousand days after. Cuvillier Verlag, Gottingen, pp 27–53Google Scholar
  5. Bitschene PR, Fernández MI, Arias N, Arizmendi A, Griznik M, Nillni A (1993) Volcanology and environmental impact of the August 1991 eruption of the Hudson volcano (Patagonian Andes, Chile). Zbl Geol Palaont Teil I H 1(2):165–177Google Scholar
  6. Bitschene PR, Sauer H, Bernard H, Sperderh, Cesari O (1995) Vegetation recuperation and improvement of Patagonian soil due to incorporation of volcanic ash of the Hudson eruption in 1991. In: Bitschene PR, Menida J (eds) 1995 The August 1991 eruption of the Hudson Volcano (Patagonian Andes): a thousand days after. Cuvillier Verlag, Gottingen, pp 55–64Google Scholar
  7. Black RA, Mack RN (1984) Aseasonal leaf abscission in Populus induced by volcanic ash. Oecologia 64:295–299CrossRefGoogle Scholar
  8. Blakemore LC, Searle PL, Daly BK (1987) Methods for chemical analysis of soils. NZ Soil Bureau Sci Rep 80:103Google Scholar
  9. Blong RJ (1984) Volcanic hazards: a sourcebook on the effects of eruptions. Academic Press, Australia 424 pGoogle Scholar
  10. Bocco G, Velázquez A, Siebe C (2005) Using geomorphologic mapping to strengthen natural resource management in developing countries: the case of rural indigenous communities in Michoacán, México. Catena 60:239–253CrossRefGoogle Scholar
  11. Boyce JK (2000) Let them eat risk? Wealth, rights and disaster vulnerability. Disasters 24(3):254–261CrossRefGoogle Scholar
  12. Bregliani M, Carmisciano P, Lamoureux M, Migliora H, Rial P, Villareal F (1993) Characteristicas de las cenizas depositadas por al volcán Hudson sobre los suelos de la Provincia de Santa Cruz y algunas consecuencias en la agricultura. Prim Jorn Volc Medio Amb Def Civ, Actas: 125–135Google Scholar
  13. Cienfuegos MS, Beltrano J (1995) Las cenizas del Volcan Hudson como sustrato para el cultivo de plantas. In: Bitschene PR, Menida J (eds) The August 1991 eruption of the Hudson Volcano (Patagonian Andes): a thousand days after. Cuvillier Verlag, Gottingen, pp 65–69Google Scholar
  14. Colton HS (1965) Experiments in raising corn in the Sunset Crater ashfall area east of Flagstaff, Arizona. Plateau 37:77–79Google Scholar
  15. Cook RJ, Barron JC, Papendick RI, Williams GJ (1981) Impact of agriculture of the Mount St. Helens eruptions. Science 211:16–22CrossRefGoogle Scholar
  16. Cronin SJ, Hedley MJ, Smith G, Neall VE (1995) Impact of Ruapehu ash fall on soil and pasture nutrient status. 1. October 1995 eruptions. NZ J Agric Res 40:383–395CrossRefGoogle Scholar
  17. Cronin SJ, Hedley MJ, Neall VE, Smith RG (1998) Agronomic impact of tephra fallout from the 1995 and 1996 Ruapehu Volcano eruptions, New Zealand. Environ Geol 34(1):21–30CrossRefGoogle Scholar
  18. Cronin SJ, Neall VE, Lecointre JA, Hedley MJ, Loganathan P (2003) Environmental hazards of fluoride in volcanic ash: a case study from Ruapehu volcano, New Zealand. J Volcanol Geotherm Res 121:271–291CrossRefGoogle Scholar
  19. Dale VH, Delgado-Acevedo J, MacMahon J (2005) Effects of modern volcanic eruptions on vegetation. In: Marti J, Ernst GGJ (eds) Volcanoes and the environment. Cambridge University Press, Cambridge, pp 227–249CrossRefGoogle Scholar
  20. Fisher RV, Heiken G, Hulen JB (1997) Volcanoes–crucibles of change. Princeton University Press, PrincetonGoogle Scholar
  21. Folsom MM (1986) Tephra on range and forest lands of eastern Washington: local erosion and redeposition. In: Keller SAC (ed) Mount St Helens: five years later. Eastern Washington University Press, USA, pp 116–119Google Scholar
  22. Fowler WB, Lopushinsky W (1986) Wind-blown volcanic ash in forest and agricultural locations as related to meteorological conditions. Atmos Environ 20(3):421–425CrossRefGoogle Scholar
  23. Georgsson G, Pétursson G (1972) Fluorosis of sheep caused by the Hekla eruption in 1970, Fourth annual conference of I.S.F.E. The Hague, 10/24–27/1971Google Scholar
  24. Grattan J, Pyatt B (1993) Acid damage to vegetation following the Laki fissure eruption in 1783—an historical review. Sci Total Environ 151:241–247Google Scholar
  25. Inbar M, Ostera HA, Parica CA (1995) Environmental assessment of 1991 Hudson volcano eruption ashfall effects on southern Patagonia region, Argentina. Environ Geol 25:119–125CrossRefGoogle Scholar
  26. Johansen CA, Eves JD, Mayer DF, Bach JC, Nedrow ME, Kious CW (1981) Effects of ash from Mt. St. Helens on bees. Melanderia 37:20–29Google Scholar
  27. Johnston DM, Houghton BF, Neall VE, Ronan KR, Paton D (2000) Impacts of the 1945 and 1995–1996 Ruapehu eruptions, New Zealand: An example of increasing societal vulnerability. Geol Soc Am Bull 112(5):720–726CrossRefGoogle Scholar
  28. Kratzmann DJ, Carey S, Scasso R, Naranjo J (2008) Compositional variations and magma mixing in the 1991 eruptions of Hudson volcano, Chile. Bull Volcanol 71(4):419–439CrossRefGoogle Scholar
  29. Luhr JF, Simkin T (1993) Parícutin, the volcano born in a Mexican cornfield, Phoenix. Geosciences Press, Wuhan, p 427Google Scholar
  30. Lyons JV (1986) Agricultural impact and adjustment to the Mount St. Helens ashfall: a search for analogs. In: Keller SAC (ed) Mount St. Helens: five years later. Eastern Washington University Press, Cheney, pp 423–429Google Scholar
  31. Mercado RA, Bertram J, Lacsamana T, Pineda GL (1996) Socioeconomic impacts of the Mount Pinatubo eruption. In: Newhall CG, Punongbayan RS (eds) Fire and mud: eruptions and lahars of Mount Pinatubo, Philippines. Philippine Institute of Volcanology and Seismology, and Seattle: University of Washington Press, Quezon CityGoogle Scholar
  32. Naranjo JA, Stern ChR (1998) Holocene explosive activity of Hudson Volcano, southern Andes. Bull Volcanol 59:291–306CrossRefGoogle Scholar
  33. Naranjo JA, Moreno H, Banks N (1993) La erupcion del volcan Hudson en 1991 (46ºS), region XI, Aisen, Chile, vol 44. Sernageomin, Santiago, p 50Google Scholar
  34. Neild J, O’Flaherty P, Hedley P, Underwood R, Johnston D, Christenson B, Brown, P (1998) Impact of a volcanic eruption on agriculture and forestry in New Zealand. MAF Policy Technical Paper 99/2, 101 pGoogle Scholar
  35. Olsen SR, Cole CV, Watanabe FS, Dean LA (1954) Estimation of available phosphorus in soils by extraction with sodium bicarbonate. United States Department of Agriculture Circular 939Google Scholar
  36. Ort MH, Elson MD, Anderson KC, Duffield WA, Hooten JA, Champion DE, Waring G (2008) Effects of scoria-cone eruptions upon nearby human communities. Geol Soc Am Bull 120(3/4):476–486CrossRefGoogle Scholar
  37. Parkinson JA, Allen SE (1975) A wet oxidation procedure suitable for the determination of nitrogen and mineral nutrients in biological material. Commun Soil Sci Plant Anal 6:1–11CrossRefGoogle Scholar
  38. Pasquini AI, Depetris PJ, Gaiero DM, Probst J (2005) Material sources, chemical weathering, and physical denudation in the Chubut River Basin (Patagonia, Argentina): implications for Andean Rivers. J Geol 113:451–469CrossRefGoogle Scholar
  39. Peri PL, Bloomberg M (2002) Windbreaks in southern Patagonia, Argentina: a review of research on growth models, windspeed reduction, and effects on crops. Agrofor Syst 56:129–144CrossRefGoogle Scholar
  40. Rees JD (1979) Effects of the eruption of Parícutin Volcano on landforms, vegetation, and human occupancy. In: Sheets PD, Grayson DK (eds) Volcanic activity and human ecology. Academic Press, New York, pp 249–292Google Scholar
  41. Reycraft RM, Bawden G (2000) Introduction. In: Bawden G, Reycraft RM (eds) Environmental disaster and the archaeology of human response. Maxwell Museum of Anthropology, Anthropological Papers No. 7, Albuquerque, pp 1–10Google Scholar
  42. Rubin CH, Noji FK, Seligman PJ, Holtz JL, Grande J, Vittani F (1994) Evaluating a fluorosis hazard after a volcanic eruption. Arch Environ Health 49(5):395–403CrossRefGoogle Scholar
  43. Scasso RA, Corbella H, Tiberi P (1994) Sedimentological analysis of the tephra from the 12–15 August 1991 eruption of Hudson volcano. Bull Volcanol 56:121–132Google Scholar
  44. Shoji S, Nanzyo M, Dahlgren RA (1993) Volcanic ash soils. Genesis, properties and utilization. Developments in soil science 21. Elsevier, AmsterdamGoogle Scholar
  45. Stewart C, Johnston DM, Leonard GS, Horwell CJ, Thordarson T, Cronin SJ (2006) Contamination of water supplies by volcanic ashfall: a literature review and simple impact modelling. J Volcanol Geotherm Res 158:296–306CrossRefGoogle Scholar
  46. Thorarinsson S (1979) Damage caused by volcanic eruptions. In: Sheets PD, Grayson DK (eds) Volcanic activity and human ecology. Academic Press, New York, pp 125–159Google Scholar
  47. Tobin GA, Whiteford LM (2002) Community resilience and Volcano Hazard: the eruption of Tungurahua and evacuation of the Faldas in Ecuador. Disasters 26(1):28–48CrossRefGoogle Scholar
  48. Ugolini FC, Zasoski RJ (1979) Soil derived from tephra. In: Sheets PD, Grayson DK (eds) Volcanic activity and human ecology. Academic Press, New York, pp 83–124Google Scholar
  49. Valdivia VHVDI (1993) Analisis Geografico del Volcan Hudson Y Sus Tipos de Riesgo. Tesis presentada para optar al titulo de Profesor de Historia, Geografia y Ed. Civica. Universidad Austral de ChileGoogle Scholar
  50. Waring G (2007) Hopi corn and volcanic cinders: a test of the relationship between tephra and agriculture in northern Arizona. In: Elson MD (ed) Sunset crater archaeology: the history of a volcanic landscape, environmental analyses. Center for Desert Archaeology, Anthropological Papers No. 33, Tucson, pp 71–84Google Scholar
  51. Wilson TM (2009) Vulnerability of pastoral farming systems to volcanic ashfall Hazards. Unpublished PhD Thesis. University of CanterburyGoogle Scholar
  52. Wilson TM, Cole JW (2007) Potential impact of ash eruptions on dairy farms from a study of the effects on a farm in eastern Bay of Plenty, New Zealand; implications for hazard mitigation. Nat Hazards 43(1):103–128CrossRefGoogle Scholar
  53. Wilson TM, Stewart C, Cole JW, Johnston DM, Cronin SJ (2010a) Vulnerability of agricultural water supplies to volcanic ash fall. Environ Earth Sci 61:675–688CrossRefGoogle Scholar
  54. Wilson TM, Cole JW, Stewart C, Johnston DM, Cronin SJ (2010b) Assessment of long-term impact and recovery of the 1991 Hudson eruption to agriculture and rural communities, Patagonia, South America. GNS Science Report 2009/66: 100Google Scholar
  55. Wilson TM, Cole JW, Stewart C, Cronin SJ, Johnston DM (2010c) Ash storm: impacts of wind remobilised volcanic ash on rural communities and agriculture following the 1991 Hudson eruption, southern Patagonia, Chile. Bull Volcanol. doi:10.1007/s00445-010-0396-1
  56. Witham CS, Oppenheimer C, Horwell CJ (2005) Volcanic ash-leachates: a review and recommendations for sampling methods. J Volcanol Geotherm Res 141:299–326CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Thomas Wilson
    • 1
  • Jim Cole
    • 1
  • Shane Cronin
    • 2
  • Carol Stewart
    • 3
  • David Johnston
    • 4
  1. 1.Natural Hazard Research Centre, Department of Geological SciencesUniversity of CanterburyChristchurchNew Zealand
  2. 2.Volcanic Risk SolutionsMassey UniversityPalmerston NorthNew Zealand
  3. 3.Private ConsultantBrooklyn, WellingtonNew Zealand
  4. 4.Joint Centre for Disaster ManagementGNS/Massey UniversityLower HuttNew Zealand

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