Structure and Evolution
One of the most active volcanoes in north Chile, Volcan Guallatiri is the youngest of a trio of stratovolcanoes, collectively known as the Nevados de Quimsachata (Figure 11.1); Cerro Acotango (A) and Cerro Elena Capurata (E) form a volcanic ridge which shows a fairly advanced state of dissection. However, the presence of a morphologically youthful lava flow on the northern flank of Acotango suggests possible Holocene activity. Guallatiri itself has had several stages of growth. Its most prominent feature is a central dacitic dome or pyroclastic cone on which a clover-leaf shaped summit lava complex is present. Terminations of young lava flows (L) can be seen on the northern and northwestern flanks (Figure 11.2) . The active vent (SC) is located on the southern side of this complex. It is possible that the central dome is located within an older amphitheatre formed by collapse of the west flank of the earlier cone, but the evidence for this is equivocal. Located near the southern (descending) limit of the tropical Hadley atmospheric circulation cell, Guallatiri is the southernmost volcano in the Central Andes to retain a permanent thick ice cap.
Casertano (1963) reported that ashes and vapours were intermittently emitted throughout the first half of the 19th century and that in 1913 and 1959 incandescent material was observed in the "smoke". This may have been the result of minor strombolian activity. Observations made in 1985 and December1987 suggested that activity then was more intense than in previous years. Emissions of whitish-yellow fumes to about 500 m above the vent occurred every 30 minutes (SEAN, Nov.,1985; Dec., 1987). Wörner et al., (pers. comm. 1989) reported the presence of a fresh obsidian bomb on the southern slopes of Guallatiri, suggesting that some explosive activity has occurred recently. Both the steam plume from the fumarole (F) and its shadow are detectable on the TM image acquired on 22nd August 1984, extending SSE from the summit. Guallatiri is one of the few catalogued volcanoes on which visible evidence of contemporary activity has been detected on the TM images.
Intense fumarolic activity persists to the present day and is prominent on the ground photograph taken in November 1985 (fig 11.2). Recent eruptive events appear to have been phreatic in origin and of short duration, lasting hours to days.
In the event of renewed activity, mudflows and pyroclastic flows might be generated which could descend the south-west flanks of the volcano via the Rio Guallatiri, threatening the hamlet of Guallatiri.
Compositions of the lavas range from andesite (58% SiO2) to rhyolite (75% SiO2; Wörner et al., pers. comm, 1989).
Casertano,L., 1963. Catalogue of the active volcanoes of the world; Part XV, Chilean continent I.A.V.C.E.I. Naples, Italy, 55pp.
Scientific Event Alert Network Bulletin, Nov 1985. V 10, no.11, p7 - 8.
Scientific Event Alert Network Bulletin, Dec 1987. V 12, no.12, p3 - 4.