Bulletin of Volcanology

, Volume 72, Issue 6, pp 641–656

Morphological complexities and hazards during the emplacement of channel-fed `a`ā lava flow fields: A study of the 2001 lower flow field on Etna

  • L. J. Applegarth
  • H. Pinkerton
  • M. R. James
  • S. Calvari
Research Article

DOI: 10.1007/s00445-010-0351-1

Cite this article as:
Applegarth, L.J., Pinkerton, H., James, M.R. et al. Bull Volcanol (2010) 72: 641. doi:10.1007/s00445-010-0351-1

Abstract

Long-lived basaltic eruptions often produce structurally complex, compound `a`ā flow fields. Here we reconstruct the development of a compound flow field emplaced during the 2001 eruption of Mt. Etna (Italy). Following an initial phase of cooling-limited advance, the reactivation of stationary flows by superposition of new units caused significant channel drainage. Later, blockages in the channel and effusion rate variations resulted in breaching events that produced two new major flow branches. We also examined small-scale, late-stage ‘squeeze-up’ extrusions that were widespread in the flow field. We classified these as ‘flows’, ‘tumuli’ or ‘spines’ on the basis of their morphology, which depended on the rheology, extrusion rate and cooling history of the lava. Squeeze-up flows were produced when the lava was fluid enough to drain away from the source bocca, but fragmented to produce blade-like features that differed markedly from `a`ā clinker. As activity waned, increased cooling and degassing led to lava arriving at boccas with a higher yield strength. In many cases this was unable to flow after extrusion, and laterally extensive, near-vertical sheets of lava developed. These are considered to be exogenous forms of tumuli. In the highest yield strength cases, near-solid lava was extruded from the flow core as a result of ramping, forming spines. The morphology and location of the squeeze-ups provides insight into the flow rheology at the time of their formation. Because they represent the final stages of activity of the flow, they may also help to refine estimates of the most advanced rheological states in which lava can be considered to flow. Our observations suggest that real-time monitoring of compound flow field evolution may allow complex processes such as channel breaching and bocca formation to be forecast. In addition, documenting the occurrence and morphology of squeeze-ups may allow us to determine whether there is any risk of a stalled flow front being reactivated. This will therefore enhance our ability to track and assess hazard posed by lava flow emplacement.

Keywords

Basaltic `a`ā Channel-fed lava Effusion rate Squeeze-up Tumuli Etna 

Supplementary material

445_2010_351_Fig1_ESM.gif (369 kb)
ESM 1

Map showing the complex post-eruption structure of the 2001 lower flow field, Mt. Etna. Contour interval is 20 m. Historic cinder cones are shown in light grey, with those mentioned in the text named. Squeeze-up flows are shown in dark grey. High relief levées and flow fronts are hatched. The locations of ephemeral boccas and squeeze-up tumuli are also shown. Short arrows show the sections over which the slope angles have been calculated; slope values in degrees are shown between these arrows. Long arrow indicates the position of the three tumuli inferred to have grown successively in section 4.2, the uppermost of which is shown in Fig. 10. Nested levées, mentioned in the text, are seen in the proximal part of the flow. ‘SP’ indicates the location of the Sapienza tourist complex, adjacent to the road the cuts through the proximal flow field. (GIF 369 kb)

445_2010_351_Fig1_ESM.tif (10.5 mb)
High Resolution Image(TIFF 10796 kb)

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • L. J. Applegarth
    • 1
  • H. Pinkerton
    • 1
  • M. R. James
    • 1
  • S. Calvari
    • 2
  1. 1.Lancaster Environment CentreLancaster UniversityLancasterUK
  2. 2.Sezione di CataniaIstituto Nazionale di Geofisica e VulcanologiaCataniaItaly

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