Global Warming May Accelerate Submarine Landslides in the Oceans -Possible Disaster Chain Reactions-

Abstract

Climate changes give affection to both atmosphere and hydrosphere. It is appeared in the form of rising both air and water temperatures on the Earth. The climate change introduces vigorous meteorological disasters in the world, such as super storms, heavy rain precipitations along linear rain belts, tornadoes and others on lands. Oceanic environments also should be affected from the climate changes. I try to figure out possible submarine hazards that may be increased in correlate to climate changes. The hazardous event may take place in the shape of disaster chain reactions as cascades.

1 Introduction

Climate changes take place in connection to air and water temperatures, carbon dioxide gas concentrations, humidity and other components on the Earth. IPCC report no. 5 (2013) made a couple of computer simulations. The simulated highest atmospheric temperature is going to increase 5.7 °C at the end of the twenty-first Century. Certainly, average temperature during 2011 to 2020 increased 1.09 °C in comparison to 1850~1900 according to IPCC no. 6 report (IPCC 2021). The climate change has certainly introduced vigorous meteorological disasters in the world, such as super storms, heavy rain precipitations along linear rain belt, tornadoes and others on lands. Oceanic environments should be affected from the climate changes.

Disastrous events have increased year by year in these decades. Interdisciplinary geo-scientists in ICSU (present ISC)-GeoUnions overviewed number of catastrophic events since 1980 up to 2015 (Cutter et al. 2015). They found that the number of disasters caused by natural events increased more than doubled since 1980 (Fig. 1). Among these, geophysical disasters, that are represented by earthquakes, tsunamis, and volcanic eruptions, were approximately doubled. In contrast, climatological, hydrological and meteorological disasters were tripled or more. This means that anthropogenic activities on Earth strongly change Earth’s environmental conditions.

Fig. 1

The number of hazards caused by natural events. Natural disasters have taken place more than doubled since 1980 up to 2015. Climate Change events are three or four times more than geophysical disasters during 35 years interval (Cutter et al. 2015). © Springer-Nature CoLtd Source: Munichre/Natcatservice

One of typical meteorological disasters is landslides at hilly areas. We should remember heavy rains- induced slope failures at Hiroshima Prefecture in 2018 and vigorous debris flows at Atami City, Shizuoka Prefecture 2021 and others.

2 Disaster Chain Reactions

Hazardous events have been increased rapidly, in these decades. Many of hazards are not occurred in a single factor but multiple factors, including anthropogenic activities either directly or indirectly in natural disaster. Artificial changes of lands sometimes cause of landslides and succeeding debris flows. Vigorous debris flow disasters at Aizome River, Atami City is a typical case of anthropogenic reasons where mass of artificial mounds were piled at the upstream area of the river. The artificial mound collapsed after heavy rains. We had been released a couple of policy briefs for reducing anthropogenic disaster risks (ISC_GU_SC_DRR, Policy Brief #05, 2021 and #06, 2022).

© Springer Nature Switzerland AG 2021. Editor 1 et al. (eds), Progress in Landslide Research and Technology, Volume 1 Issue 1, 2022, Book Series of the International Consortium on Landslides. DOI 10.1007/978-94-007-2162-3_36.

3 Gas Hydrate May Introduce Submarine Landslide

As one of typical multiple hazards, we focus in gas hydrates. There are gas hydrates bearing strata at sea floor. Unstable gas hydrate should be produced submarine landslides.

Gas hydrate stability is decided with both hydraulic pressure and water temperature of the sea. Unstable conditions of strata may start around 1000 m in water depth. Stability of sedimentary bodies are developed slope basins, in particular deep in the sea.

Figure 2 shows physic-chemical model for gas hydrates bearing sea floors. Above 1000 m deep in seas, sediments that are bearing gas hydrates are unstable due to melting hydrates. When gas hydrates liquidize, sedimentary bodies may become unstable conditions. This liquefaction of hydrates from solid to gaseous conditions introduces unstable slope conditions and then slope destructions may take place.

Fig. 2

Gas hydrate stability zone at continental margin areas (Ruppel and Kessler 2016)

Figure 3 shows global distribution map of the gas hydrate stability zone. Referring from Fig. 4, gas hydrate accumulates thickly in the permafrost areas both at Arctic and Antarctic regions. In contrast, gas hydrates are distributed along continental slope areas of both temperate to tropical area of the seas. Continental shelf to slope areas, slope failures may take place as gravity flows. Two triggers of slope failures may take place. The one is non-tectonic landslides, and the other is Earthquake-induced landslides. “Non-tectonic” means the cause that is not induced by the Earthquake shakes.

Fig. 3

Global distribution maps of the gas hydrate stability zone. Red color shows the reducing (both emission and accumulation balance) of gas hydrate regions. They are either permafrost or shallow polar seas. Blue shows the accumulating of gas hydrate. They are distributed in either middle to low latitude continental slopes of the Earth. (Ruppel and Kessler 2016)

Fig. 4

Gas hydrate stability zone on the Earth, in particular to terrestrial zone to the ocean floor, and from subpolar permafrost and deep-sea where thick piles of gas hydrates develop. (Ruppel and Kessler 2016)

Fig. 5

Cartoon shows Oxygen Minimum Zone at forearc basin where diatomaceous muddy sediments are thickly deposited. Gas hydrate develops under OMZ. Red line in the cartoon shows Bottom Seismic Refraction (BSR) horizons, bottom limit of gas hydrate in sediments. The basic geologic features were drawn by Dr. Asahiko Taira

When water temperatures both in seas and lakes rise due to climate changes, it may introduce unstable sedimentary slopes where are bearing gas hydrates. Slope instabilities progress in connection to global climate changes even at sea floors. If heavy Earthquake takes place at unstable slope areas in the sea, it may also be induced tectonic landslides at sea floor and may generate Tsunami events.

Another possible cause of landslides is “artificial” changes of ground surfaces due to the anthropogenic activities. Recent years, artificial changes of the Earth’s surface are frequently taken place at everywhere in the world. They should be the cause of unstable environment. They should introduce landslides and/or debris flows after heavy rain precipitations or Earthquake shakings.

As shown above, series of natural and anthropogenic hazards should cause big debris flows or landslides. Finally, it may generate anthropogenic disasters.

Disastrous events are not occurred by a single reason. Disaster chain reactions may be occurred by various causes as follows. It is well known that global warming raises up atmospheric temperatures. It introduces increase of atmospheric humidity’s according to increase of evaporation amount from the Earth’s surface, in particular to oceanic surface. These reactions take place around the world mostly at the same time. These phenomena should induce heavy rain precipitations and further introduces high water contents of soils and basement rocks. Series of natural responses should be triggers for landslides or debris flows at different shapes not only at terrestrial realms, but also at oceanic realms and or big lake regions.

4 Case Studies of Landslides in Connection to the Global Warnings

We can show a couple of case studies in connection to climate changes globally. Slope failures and succeeding big Tsunamis took place at the Storegga slope basins off.

Norway, 5000 years before. Tsunami deposits are widely distributed in the areas of both Norway and northern part of Great Britain Islands (Dawson et al. 2020). The Storegga region is well-known area where gas-hydrates bearing sediments distributed in slopes. It is probable to occur submarine landslide due to slope instabilities by the melting of gas hydrates. However, direct cause has not yet. Earthquakes? Iceberg scrapes slope sediments? or gravity flow took place in relation to the global warnings? We should continuously analyze what is the real reason of the Storegga landslides as discussed by Løvholt et al. 2017. Similar slope failures were known at Baiyun-Liwan submarine landslide off China on early Miocene (Zhu et al. 2019).

Fossil landslide layers are frequently found in the late Cenozoic marine sedimentary sequences. Kremer and others pointed out the landslide layers coincide well with interglacial times (Kremer et al. 2017). Similar submarine landslide deposits were described at the late Cenozoic marine sequences at Boso Peninsula (Mitsunashi et al. 1962).

Majima et al. (2019) and Nozaki et al. (2019) studied chemosynthetic clam communities from the Quaternary sedimentary sequences at the Boso and Miura Peninsulas, Central Japan. The clam fossil colony distributed horizons roughly coincide well with interglacial horizons. It can be explained that outgoing methene fluxes from sediments increase during interglacial time. Because methene should be provided due to the collapse of gas hydrate. These cases show that landslides should be caused in connection to global warnings.

How can we construct sedimentary models for explaining submarine landslides at continental slopes. I propose the following environmental-tectonic model for submarine landslides in particular to active margin area such as Pacific rims (Fig. 5).

This model (Fig. 5) shows eutrophic continental slope to the trench environments such as the Kuril and Japanese Island Arcs where organic rich sediments are thickly deposited along the slope basins. High organic flux sustained by the high primary production such as diatom or other phytoplankton blooms. As a result, Oxygen Minimum Zone (OMZ) where low dissolved oxygen concentration layer develops at the upper to middle bathyal depths. OMZ mostly coincides with the depths of the upper limit of gas hydrate stable zone. When global warming progresses, unstable physic-chemical gas hydrate conditions, should start from shallower to deeper depths in the oceans. Slope failure and possible submarine landslides may highly probable to take place at upper bathyal depths in connection to sea water temperature rise.

On 2023, water temperature is high in the southern part of the Japanese Islands where western Pacific is distributed. Kuroshio Current flows further north in comparison to the normal year. These conditions may be introduced unstable bottom environments. Chain reaction in connection to global warmings are highly probable to take place along the middle to low latitude of the oceans. We should keenly watch climate changes on the Earth, not only on land but also in the sea further to the deep-sea.

5 Concluding Remarks

Submarine landslides are used to be explained by tectonic induced model in the sea. Continental slope basins shake strongly by vigorous Earthquakes and slope failures took place at continental slopes. Great East Japan Earthquake on 2011 should give nice case studies. Earthquakes and succeeding landslides observed at trench axial zone where oceanic plate subduct under the Japanese Islands. This is obviously a tectonic origin. However, slope basins off Tohoku in the Pacific Ocean are the area of active sedimentations. Tohoku area is an area for high in surface primary production. Eutrophic ocean produces a lot of organic carbon due to high rate of primary production and forms organic rich sediments. Forearc basin of the Northeast Japan is characterized by high concentration of organic carbon and should be gas-hydrate bearing sedimentary sequences potentially.

One probable scenario for forming frequent submarine landslides at Tohoku area can be figured out as follows. Primarily, slope sediments contain high organic carbon. It may introduce gas-hydrate bearing deposits. Gas-hydrate bearing strata is unstable and it is potential to produce gravity flows when big earthquakes are being occurred. Submarine landslides sometimes induce Tsunamis, so that disaster chain reactions may take place at the areas. We should keenly watch these disaster chain reactions at the active tectonic margin for decreasing disaster risk reduction.

Appendices

Storegga Slide and Landslide-Induced Tsunamis

Stregga slide: from Locat J. and Lee H. (2008) Submarine Mass Movements and Their Consequences: An Overview. Landslides- Disaster Risk Reduction (eds: Sassa K, Canuti P.): 115–142.

3-D View of the Storegga landslide: from Talling, P.J.; Clare, M.; Urlaub, M.; Pope, E.; Hunt, J.E.; Watt, S. Large Submarine Landslides on Continental Slopes Geohazards, Methane Release, and Climate Change. Oceanography 2014, 27, 32–45.

Gas Hydrate Melting Processes

Gas hydrate melting processes that may cause submarine landslides or cause methane emissions: from Talling, P.J.; Clare, M.; Urlaub, M.; Pope, E.; Hunt, J.E.; Watt, S. Large Submarine Landslides on Continental Slopes Geohazards, Methane Release, and Climate Change. Oceanography 2014, 27, 32–45.