Character, stratigraphy and magnitude of historical lahars of Cotopaxi volcano (Ecuador)

Abstract:

Since 1534, Cotopaxi Volcano, Ecuador has produced five eruptive periods with numerous vei 3-4 eruptions, all of andesitic affinity. Due to melting of the glacier cap by pyroclastic flows, voluminous lahars formed and flowed for hundreds of kilometers, passing through the Chillos and the Latacunga Valleys via major drainages. The most distinctive lahar deposit is that of the June 26th 1877 eruption. This lahar was characterized by carrying numerous scoria blocks, a factor which greatly facilitated its mapping. Granulometric analysis of the 1877 and the earlier 18th century deposits show that lahars begin as clast-rich, granular debris flows that were non-cohesive (< 5% clay-size particles) near the source and were in the process of transforming to hyperconcentrated flow at distal points. Indirect velocity computation for lahars based on run-ups ranged from 5-23 m/s. Results of mapping 83 stream profiles, in which …

Año de publicación:

2004

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