DO GLACIATION-DEGLACIATION CYCLES LEAD TO CLUSTERING VOLCANIC ERUPTIONS AND CALDERA FORMATION?

New Ar-Ar, U-Pb, and 14-C ages of caldera-forming eruptions in glaciated arc of Kamchatka demonstrates that the majority of large-volume ignimbrites, in vicinity of morphologically-preserved calderas, correspond in the time with "maximum glacial" conditions. The latter is defined as coincidence of the eruption ages with the highest 18-O foraminifera values on the N Pacific SPECMAP stack. The strongest field evidence comes from glaciated multi-caldera volcanoes, that hosted thick glacial ice caps. Here we present a set of new results from numerical modelling using a finite element method that investigates how the glacial load dynamic may affect the conditions for ring-fault formation and alter eruption frequency in such glaciated multi-caldera volcanoes. All numerical models are two-dimensional assuming plane strain and considering that the surrounding crust behaves as a linear homogeneous elastic material. Different scenarios were simulated by varying i) the thickness ranging from 0 to 1 km) of the ice caps on top of the pre-existing collapse calderas, ii) the sizes of the pre-existing collapse structures (from 5 to 40 km in diameter) and iii) the depth of the magmatic reservoir responsible for the subsequent collapse event. We also investigate effects the asymmetric distribution of ice, and a variable pre-caldera topography. Results indicate that for a given geometrical set-up , the magnitude and position of maximum tensional stress at the Earth's surface are influenced by the occurrence and relative distribution of the ice caps. We find that: 1) the existence of ice caps do not favor the formation ring-fault propagation and caldera formation; 2) asymmetric distribution of ice plays no or minor role; 3) Glacial erosion of part of volcanic edifice or interglacial edifice failure may promote ring fracture; 4) freezing the upper portion of hydrothermal system may lead to steeper temperature gradient and more acidic hydrothermal fluids; 5) hydrothermal rotting of the intracaldera rocks under the ice cap is more important; 6) ice overload may lead to accumulation of gas in magma; 7) short period interstadial during maximal glaciation may play most important role in rapid decompression. These observations suggest multiple positive and inhibiting feedbacks between the ice caps and calderas in influencing the stress field conditions required for ring-fault formation.