Role of large flank-collapse events on magma evolution of volcanoes. Insights from the Lesser Antilles Arc
Abstract
Flank-collapse events are now recognized as common process of destruction of volcanoes. They can occur several times on a volcanic edifice and may involve a large range of volume of material from km3 to thousands of km3. Large flank-collapse events may have significant effects on magma eruption and evolution. The load exerted by the volcanic edifice on the plumbing system and the magma chamber acts as a density filter for magma ascent. Magmas denser than the density threshold are stored within the magma chamber where they differentiate and thus become less dense with time which favours their eruption. When a flank-collapse event occurs the edifice load suddenly decreases which decreases the density threshold allowing denser magmas to ascend and erupt. Thus construction and destruction of volcanic edifices may control both differentiation and eruptive processes. In the Lesser Antilles Arc, a large number of flank-collapse events have been identified. Here, we show that some of the largest events are correlated to significant variations in erupted magma compositions and eruptive styles. On Montagne Pelée, after the 32 kys old flank-collapse event, the magma production rate is sustained during several thousand years: basic and dense magmas were emitted through open-vent eruptions that generated abundant scoria flows. The pre-flank collapse activity produced significantly more acidic magmas. The rapid building of a new cone after the flank collapse progressively increased the load and the density threshold, leading to a decrease in magma production rate and a change in the magma composition of the erupted products. They are more acidic and less dense and thus generate plinian and dome-forming eruptions up to present. On the contrary, at Soufrière Volcanic Centre of St Lucia and at Pitons du Carbet in Martinique, the flank collapses have an opposite effect: in both cases, more acidic magmas erupted after the flank collapse events. These magmas are highly crystallized (up to 60 %) and much more viscous that the magmas erupted before the flank-collapse. They have been generally emplaced as voluminous and uptight lava domes (called "the Pitons"). Such magmas could not ascent without a significant decrease of the threshold effect produced by the volcanic edifice before the collapse.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V43G..05B
- Keywords:
-
- 8413 VOLCANOLOGY / Subduction zone processes;
- 8414 VOLCANOLOGY / Eruption mechanisms and flow emplacement;
- 8434 VOLCANOLOGY / Magma migration and fragmentation;
- 8455 VOLCANOLOGY / Tephrochronology