2003 Seattle Annual Meeting (November 25, 2003)
Paper No. 188-7
Presentation Time: 1:30 PM-5:30 PM


LUNDBERG, Joyce, Carleton Univ, Dept Geography, Ottawa, ON K1S 5B6, Canada, joyce_lundberg@carleton.ca and MCFARLANE, Donald, Keck Science Center, The Claremont Colleges, 925 North Mills Avenue, Claremont, CA 91711

The eastern flanks of Mt. Elgon, a ~4000 km2, 4321 m early Miocene stratovolcano, are penetrated, at altitudes of 2400-2500 m, by several voluminous caves up to ~160 m long, ~80 m wide, and 20 m high. These caves are regularly visited by a variety of animals including elephants which 'mine' the pyroclastic bedrock for its content of sodium-calcium-rich salts. Since the first written descriptions in the late 19th Century, their origin has been debated. Some authors have argued for primarily zoogeomorphic speleogenesis, whilst others have argued for primarily dissolutional origin with only secondary modification by elephants. We report the first serious mapping and geomorphological study of the caves. Cave development is strongly related to lithology. Percolation is limited to a lower ~1-2 m swelling-clay tuff and upper ~0-30 cm baked paleosol. These are separated and overlain by pyroclastic agglomerates of varying mineralogy and hardness. Caves develop behind waterfalls under surface stream valleys, by groundwater sapping, usually of the highly incompetent clay. This is followed by collapse of overlying agglomerate layers. The dominant passage shape is breakdown dome, with abundant fresh collapse blocks. Geophagy by elephants and other species, and some human mining for salts, significantly modify and enlarge the caves. These activities, focused on accessible and salt-rich units, create sizeable quasi-horizontal undercuts (up to ~3 m tall and deep), the locus moving upwards as collapse raises the floor. Significant erosion also occurs by biogeochemical activity from huge bat colonies. Pressure release jointing, efflorescence and flaking also occur. This ongoing removal of material allows continued collapse, while lateral extension continues as the clay unit fails. Quaternary glaciation and deglaciation may have modified the balance of speleogenetic processes by alternately reducing animal activity and increasing water flow. No evidence was found of phreatic or vadose activity, although round tree-trunk moulds superficially resemble phreatic tubes, while elephant-worn pathways may resemble vadose channels.

2003 Seattle Annual Meeting (November 25, 2003)
Session No. 188--Booth# 61
Quaternary Geology/Geomorphology (Posters) III: Glaciers, Volcanoes, Caves, and Isotopes
Washington State Convention and Trade Center: Hall 4-F
1:30 PM-5:30 PM, Tuesday, November 4, 2003

Geological Society of America Abstracts with Programs, Vol. 35, No. 6, September 2003, p. 422

© Copyright 2003 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.