But the dangers don't stop there. Clays, in a collapse of a volcanic edifice, can increase the runout of the debris or mudflow that may result; this occurred in Nicaragua in 1998 at the Castia volcano, when a hurricane caused part of an old lava dome complex to collapse, and the smectite clays that had formed in the domes from hydrothermal processes helped form a massive lahar that traveled more than 10 km. It's also a concern at a number of Cascade volcanoes, including Mount Rainier; even if the volcanoes haven't erupted in a long time, there are still active hydrothermal systems within their flanks, altering the volcanic rocks there to weaker materials. Multiple studies have attempted to map these alteration zones and determine where a collapse might occur based on the location and extent of particular clay minerals.
Crowley, J.K., Hubbard, B.E. and Mars, J.C., 2003. Analysis of potential debris flow source areas on Mount Shasta, California, by using airborne and satellite remote sensing data. Remote Sensing of Environment, 87(2-3): 345-358.
John, D.A., Sisson, T.W., Breit, G.N., Rye, R.O. and Vallance, J.W., 2008. Characteristics, extent and origin of hydrothermal alteration at Mount Rainier Volcano, Cascades Arc, USA: Implications for debris-flow hazards and mineral deposits. Journal of Volcanology and Geothermal Research, 175(3): 289-314.
Opfergelt, S., Delmelle, P., Boivin, P. and Delvaux, B., 2006. The 1998 debris avalanche at Casita volcano, Nicaragua: Investigation of the role of hydrothermal smectite in promoting slope instability. Geophysical Research Letters, 33(15): 4.
Reid, M.E., Sisson, T.W. and Brien, D.L., 2001. Volcano collapse promoted by hydrothermal alteration and edifice shape, Mount Rainier, Washington. Geology, 29(9): 779-782.
Sheridan, M.F. et al., 1999. Report on the October 30 1998 rockfall/debris avalanche and breakout flow of Casita volcano, Nicaragua, triggered by Hurricane Mitch. Landslide News, 12: 2-4.
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