Publication Date:
2017-04-04
Description:
Basaltic 'a'ā lava flows often demonstrate compound morphology, consisting of many juxtaposed and
superposed flow units. Following observations made during the 2001 eruption of Mt. Etna, Sicily, we
examine the processes that can result from the superposition of flow units, when the underlying units are
sufficiently young to have immature crusts and deformable cores. During this eruption, we observed that
the emplacement of new surface flow units may reactivate older, underlying units by squeezing the still-hot
flow core away from the site of loading. Here, we illustrate three different styles of reactivation that depend
on the time elapsed between the emplacement of the two flow units, hence the rheological contrast between
them. For relatively long time intervals (2 to 15 days), and consequently significant rheological contrasts,
superposition can pressurise the underlying flow unit, leading to crustal rupture and the subsequent
extrusion of a small volume of high yield strength lava. Following shorter intervals (1 to 2 days), the
increased pressure caused by superposition can result in renewed, slow advance of the underlying
immature flow unit front. On timescales of 〈 1 day, where there is little rheological contrast between the
two units, the thin intervening crust can be disrupted during superposition, allowing mixing of the flow
cores, large-scale reactivation of both units, and widespread channel drainage. This mechanism may
explain the presence of drained channels in flows that are known to have been cooling-limited, contrary to
the usual interpretation of drainage as an indicator of volume-limited behaviour. Because the
remobilisation of previously stagnant lava can occur swiftly and unexpectedly, it may pose a significant
hazard during the emplacement of compound flows. Constant monitoring of flow development to identify
areas where superposition is occurring is therefore recommended, as this may allow potentially hazardous
rapid drainage events to be forecast. Reactivation processes should also be borne in mind when
reconstructing the emplacement of old lava flow fields, as failure to recognise their effects may result in the
misinterpretation of features such as drained channels.
Description:
The work was funded by NERC studentship NER/S/A2005/13681 and
grant NE/F018010/1.
Description:
Published
Description:
1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
Description:
JCR Journal
Description:
open
Keywords:
Etna
;
flow unit
;
compound flow
;
superposition
;
04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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