 |
| Titel |
Forecasting volcanic eruptions: the narrow margin between eruption and
intrusion |
| VerfasserIn |
Alexander Steele, Christopher Kilburn, Richard Wall, Danielle Charlton |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124628
|
| Publikation (Nr.) |
 EGU/EGU2016-4089.pdf |
|
|
|
|
|
| Zusammenfassung |
| Volcano-tectonic (VT) seismicity is one of the primary geophysical signals for monitoring
volcanic unrest. It measures the brittle response of the crust to changes in stress and provides
a natural proxy for gauging the stability of a pressurizing body of magma. Here we apply a
new model of crustal extension to observations from the 2015 unrest of Cotopaxi, in Ecuador.
The model agrees well with field data and is consistent with accelerating unrest during the
pressurization and rupture of a vertically-extended magma source within the volcanic
edifice.
At andesitic-dacitic stratovolcanoes in subduction zones, unrest after long repose is often
characterised by increases in VT event rate that change from an exponential to hyperbolic
trend with time. This sequence was observed when renewed unrest was detected in April
2015 at Cotopaxi, following at least 73 years of repose. After about 80 days of elevated
seismicity at an approximately steady rate, the numbers of VT events increased
exponentially with time for c. 80 days, before increasing for c. 15 days along a faster,
hyperbolic trend. Both trends were characterised by the same value of 2 for the
ratio of maximum applied stress SF to tensile strength of the crust σT, consistent
with the pressurization of an approximately vertical, cylindrical magma body. The
hyperbolic trend indicated a potential rupture on 25 September. Rupture appears to have
occurred on 21-22 September, when the VT rate rapidly decreased. However, no major
eruption accompanied the change, suggesting that a near-surface intrusion occurred
instead.
Although the quantitative VT trends were consistent with the rupture of a magmatic body,
they could not on their own distinguish between an eruptive or intrusive outcome. An
outstanding goal remains to identify additional precursory characteristics for quantifying the
probability that magma will reach the surface after escaping from a ruptured parent body.
Data for this analysis were kindly made available by the Instituto Geofísico in Quito,
Ecuador (www.igepn.edu.ec). |
|
|
|
|
|
|