7a. Volcan Copahue is a 3 km high quaternary volcano situated in a 20 km diameter caldera at the eastern side of the Andes (about 37 oS). The volcano is built of breccias and lava flows with a base of lahar and debris flows.  The volcano is rounded by past glacier actions, with a small modern glacier and a row of cinder cones from the yougest eruptions at the summit. The summit crater lake of about 200 m diameter is bordered by the glacier and phreatic debris layers. The water temperature varies between 25 and 55 oC and has a pH value of ~0.3. Fluids discharging from springs in the summit region feed the Rio Agrio, which acidifies the large glacial "two-finger" Lake Caviahue in the caldera plain. The lake exploded in 1992 and 1995-1996. The watercolumn was instantaneously turned into steam, creating a huge white vapor plume lumbering over the landscape. Small nodules of chilled sulfur and lake bed sediments are ejected as well, creating a dark fall-out lobe on the bright white snow cover. Rare juvenile clasts were observed in the deposits. On 1 July, 2000, Copahue started a series of eruptions that culminated in ash beds over much of the caldera region, incandescent bombs and debris, lasting till October 2000. The lake was thrown out as well but had re-establsihed itself in January 2001.

We study the element fluxes, the rates and extent of acid water-rock interaction and time series of the lake composition as a volcano monitoring tool. The concentration and fluxes of some elements increased dramatically just prior to the 2000 eruption, signalling the intrusion of new magma into the hydrothermal system. We started a weekly monitoring effort in February 2001 on the composition of the Rio Agrio in conjunction with Sr. Adrian Calcagno from Caviahue village (see Results)
 


 

For pictures of the 2000 eruptions go to Copahue Eruptions


 Photo by Jane Coffey

A cascade of 'battery acid': the Rio Agrio with a pH ~ 0.5 on Volcan Copahue, Argentina. The trees are the "living fossils" Auracaria auracana, already occurring in Mesozoic times. Many yellowish efflourescent minerals (e.g., halotrichite, copiatite) grow on the rocks as a result of splash evaporation. See the article and photographs on these remarkable trees (the Pehuen) by our friend Jane Coffey in "The Archaic, Enduring Pehuen" in Orion magazine, Autumn 2000, p.12-14.
 


The 1997 Copahue fieldtrip
 
 
 

Sampling the lake fluids of Copahue crater lake (pH ~ 0.3, T = 60 oC)
 

Copahue crater lake with glacier in the back and HCl fumes evading from the lake surface
 
 


Glacial lake Caviahue, near Copahue, with a pH of ~2.6
 
 

BACK TO JOOP