Flank collapse triggered by intrusion: the Canarian and Cape Verde Archipelagoes

被引:98
作者
Elsworth, D [1 ]
Day, SJ
机构
[1] Penn State Univ, Dept Energy & Geoenvironm Engn, University Pk, PA 16802 USA
[2] Cheltenham & Gloucester Coll Higer Educ, Dept Geog & Geol, Cheltenham, Glos, England
[3] UCL, Benfield Greig Hazard Res Ctr, London, England
关键词
aquathermal; poromechanics; flank instability; Fogo; Cumbre Vieja;
D O I
10.1016/S0377-0273(99)00110-9
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
The potential to develop kilometer-scale instabilities on the flanks of intraplate volcanoes, typified by the Canary and Cape Verde Archipelagoes, is investigated. A primary triggering agent is forced injection of moderate-scale dikes, resulting in the concurrent development of mechanical and thermal fluid pressures along the basal decollement, and magmastatic pressures at the dike interface. These additive effects are shown capable of developing shallow-seated block instabilities for dike thicknesses of the order of 1 m, and horizontal lengths greater than about 1 km. For dikes that approach or penetrate the surface, and are greater in length than this threshold, the destabilizing influence of the magmastatic column is significant, and excess pore fluid pressures may not be necessary to initiate failure. The potentially destabilized block geometry changes from a flank-surface-parallel sliver for short dikes, to a deeper and less stable decollement as dike horizontal length builds and the effects of block lateral restraint diminish. For intrusions longer than about 1 km, the critical basal decollement dives below the water table and utilizes the complementary destabilizing influences of pore fluid pressures and magma "push" at the rear block-scarp. In addition to verifying the plausibility of suprahydrostatic pressures as capable of triggering failure on these volcanoes, timing of the onset of maximum instability may also be tracked. For events within the Cumbre Vieja (1949) and Fogo (1951, 1995) pre-effusive episodes, the observation of seismic activity within the first 1 week to 4 months is consistent with the predictions of thermal and mechanical pressurization. (C) 1999 Elsevier Science B.V. All rights reserved.
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页码:323 / 340
页数:18
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