File:The Andes of southern Peru, geographical reconnaissance along the seventy-third meridian (1916) (14802501483).jpg

Identifier: andesofsouthernp00 (find matches)
Title: The Andes of southern Peru, geographical reconnaissance along the seventy-third meridian
Year: 1916 (1910s)
Authors: Bowman, Isaiah, 1878-1950 American Geographical Society of New York
Subjects: Yale Peruvian Expedition (1911) Physical geography Geology Human geography
Publisher: (New York) Pub. for the American Geographical Society of New York by H. Holt and Company
Contributing Library: Wellesley College Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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d in verylow latitudes it is necessary to turn aside for a moment and con-sider two rival hypotheses of glacial retreat. First we have thehypothesis of periodic retreat, so generally applied to terminalmoraines and associated outwash in glaciated mountain valleys.This implies also an advance of the ice from a higher position,the whole taking place as a result of a climatic change fromwarmer to colder and back again to warmer. But evidences of more extensive mountain glaciation in thepast do not in themselves prove a change in climate over the wholeearth. In an epoch of fixed climate a glacier system may so deeplyand thoroughly erode a mountain mass, that the former glaciersmay either diminish in size or disappear altogether. As the workof excavation proceeds, the catchment basins are sunk to, and atlast below, the snowline; broad tributary spurs whose snowsnourish the glaciers, may be reduced to narrow or skeleton ridgeswith little snow to contribute to the valleys on either hand; the
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Fig. 137. Fig. 138. Fig. 137—Looking up a spurless flat-floored glacial trough near the Chucuito passin the Cordillera Vilcapampa from 14,200 feet (4,330 m.). Note the looped terminaland lateral moraines on the steep valley wall on the left. A stone fence from wall towall serves to inclose the flock of the mountain shepherd. Fig. 138—Terminal moraine in the glaciated Choquetira Valley below Choquetira.The people who live here have an abundance of stones for building corrals and stonehouses. The upper edge of the timber belt (cold timber line) is visible beyond thehouses. Elevation 12,100 feet (3,690 m.). EASTERN ANDES: CORDILLERA VILCAPAMPA 209 glaciers retreat and at last disappear. There would be evidencesof glaciation all about the ruins of the former loftier mountain,but there would be no living glaciers. And yet the climate mightremain the same throughout. It is this topographic hypothesis that Reiss and Stiibelaccept for the Ecuadorean volcanoes. Moreover, the volcanoes ofEc

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