Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p32d0570s&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P32D-0570
Other
5480 Volcanism (8450), 8450 Planetary Volcanism (5480)
Scientific paper
The collapse of volcanic edifices on Earth commonly results in the formation of debris avalanche deposits. Jocotitlán Volcano in Mexico (Siebe et al., 1992) and Shiveluch Volcano in Kamchatka (Belousov et al., 1999) provide remarkably preserved features at several scales that reveal the mechanism of failure and transport of materials. Structures of the remaining edifices on these two volcanoes and characteristics of their deposits are consistent with the model of edifice failure accepted for the 1980 collapse of Mount St. Helens (Voight et al., 1983). Jocotitlán and Shiveluch provide good analogues for deposits of suspected similar origin on Mars, Venus or other planets with large volcanic constructs. Jocotitlan represents a more homogeneous source of layered andesitic lavas whereas the source at Shiveluch was a dacitic dome complex of texturally heterogeneous materials. Both volcanoes have well-preserved summit scarps and display large blocks of materials that slid to a resting place within a few kilometers of the breakaway wall. The volume of collapsed and transported materials in both cases is a few km3 and their deposits from a fan extending for 10-15 km with a H/L value of 0.11. The following features were recognized on the surface of either one or the other of these deposits: numerous flow lobes with different composition and textural characteristics, cross-cutting relationships between flow lobes, steep flow fronts, lateral ridges similar to levees, high bounding ridges at the crater mouth, shadow zones behind large mounds in which vegetation was protected, deep grooves between flow lobes filled with large boulders, tensional gashes sub-normal to flow direction, large blocks consisting of fragile materials that were pushed laterally towards the deposit margin, and decomposition of large coherent surface blocks into conical mounds of fragments. Hummocks are particularly obvious at Jocotitlán Volcano where they are of the size of cinder cones. Where erosion has locally cut through the deposits several important stratigraphic features are present: local sections consisting of several emplacement units, vertical size and textural gradations within units, ramp structures between units, preservation of a thin layer of organic material above an ash layer beneath the debris, and local erosion of older deposits. The mechanism for generation and emplacement of these deposits is progressive collapse of the edifice into large blocks that slide downslope. Trailing blocks come to rest more or less intact, but the leading materials progressively disintegrates into finer material. Lateral levees, ramp structures, tension gashes attest to the yield strength of the flowing materials. Rapid deceleration of the flow terminus is evidenced by local thrust faulting and vaulting of surficial blocks ahead of the flow and a bulldozer effect on underlying sediments.
Farley M.
Sheridan Michael F.
Siebe C.
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