Why are some volcanoes more likely to collapse?
Fr, 23. Okt 2020, 10:2610:26 AM | VON: ELEANOR
One of the worst things that can happen to a volcano and anyone nearby is when larger parts of the volcano collapse, creating catastrophic landslides or debris avalanches, usually along with powerful explosive eruptions. The 1980 eruption of Mt. St. Helens was such a case. Fortunately, such events are very rare, but their hazard is much greater than most other types of volcanic eruptions.
Island of La Palma in the Canaries, Volcán Taburiente in background – study site for research by Thiele et al. (2020) (Image: Global Volcanism Program)
It is therefore important to identify volcanoes which might be more likely to undergo collapse than others. One clue seems to be coming from investigating the history of magma intrusions at a given volcano during its long-term past.
Using ground-breaking three-dimensional digital mapping techniques (UAV surveys), scientists at Monash University have revealed the possible long-term effects of magma movement within a volcanic edifice.
Stress accumulates within densely intruded regions of a volcano – a result of repeated movement of magma within the intrusion framework – blocking subsequent dyke formation thus leading to the migration of eruptive activity and the evolution of long-lived volcanic systems. Volcanoes experiencing such behaviour may be considered 'stressed'and unstable.
Volcanic collapse is considered by volcanologists as the worst-case scenario during an eruptive event, potentially triggering tsunami and pyroclastic flows; two of the deadliest volcanic hazards. As stated by Dr Sam Thiele, lead author of this study, 'research on volcano growth helps us to understand these internal processes and the associated forces that could trigger a deadly collapse or eruption'.
Temporally and spatially interconnected dykes (vertical intrusions), sills (lateral intrusions) and magma chambers create a volcano's magma plumbing system. These intrusions form an internal structure within the volcano and exert fundamental controls on volcanic behaviour, influencing and reflecting edifice processes. In doing so they provide a record of volcano dynamics and long-term evolution that is essential for the development of predictive models.
This innovative study, published in Scientific Reports, explored the mechanisms that control and accommodate dyke injections, using Volcán Taburiente on La Palma, Canary Islands, as its study site. The thickness of intrusions was measured, and excess magma pressure was calculated based on the ratio between dyke aperture and length. The strain accommodated by accumulated elastic stresses in the edifice and ductile/plastic deformation can be combined in a Maxwell visco-elastic model that estimates the edifice stresses. As forces build up, the volcano becomes 'stressed'.
The study concludes the stresses induced by successive intrusions accumulate in volcanic edifices and influence dyke propagation paths and apertures. Stress fields within heavily intruded regions may significantly differ from lithostatic model predictions. Stress plug development by this mechanism may be an important and widespread control on the spatio-temporal distribution of volcanism in long-lived volcanic systems. It was found that volcanoes gradually become 'stressed'through repeated magma movement, potentially destabilising the whole volcano and therefore influencing future collapses and eruptions.
This research facilitates our understanding on volcanic collapse and exemplifies the significance of UAV technology as a tool for potentially predicting the evolution and stability of long-lived volcanic systems around the world.
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Mo, 5. Okt 2020, 09:05
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