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Les cendres volcaniques de la vallée du Cachapoal-Rappel (Chili)

1971; Laval University; Volume: 15; Issue: 35 Linguagem: Inglês

10.7202/020962ar

1708-8968

Romulo Santana-Aguilar,

Geological and Tectonic Studies in Latin America

THE VOLCANIC ASH OF THE CACHAPOAL-RAPEL VALLEY (CHILE) Over a distance of about 90 miles, from the Andean valleys of the Pangal and the Cachapoal as far as the gorge of the Rio Rapel on the Coastal Plains, there are areas of terraces, hills and plains formed from the volcanic ash which is evidence of large scale eruptions. Forms and deposits of the same type are found in the valley of the Maipo on the fringe of the Argentinian Piedmont. Sediments typical of this eruption are formed for the large part from pumice stone and volcanic glass. On the whole, it is of a whitish colour which weathering turns to brown. Sections reveal a loose non-stratified mass, covered with a thick illuvial crust, several metres in thickness. Some coarse facies are juxtaposed to ash accumulations. These facies are formed of shingles and boulders. Others are exclusively of pumice stone. The volcanic ash probably spread from the Maipo volcano in the form of large, cool, viscous flows (lahars). This process explains the position of the ash along the axis of the large rivers, the valley heads of which are near the Maipo on the Western slope and LIaucha Papagayos and Diamante in the eastern part of the Andes.