HR: 1400h
AN: V33B-02 INVITED     [Abstracts]
TI: Rapid Loss of Andean Alpine Glaciers: A Reflection on Cotopaxi´s Long-Distance Historical Lahars and Future Lahar Scenarios
AU: * Mothes, P A
EM: pmothes@igepn.edu.ec
AF: Instituto Geofisico, Escuela Politecnica Nacional, Quito, 1701-2759, Ecuador
AU: Hall, M L
EM: mhall@igepn.edu.ec
AF: Instituto Geofisico, Escuela Politecnica Nacional, Quito, 1701-2759, Ecuador
AU: Samaniego, P
EM: psamaniego@igepn.edu.ec
AF: Instituto Geofisico, Escuela Politecnica Nacional, Quito, 1701-2759, Ecuador
AU: Francou, B
EM: bernard.francou@ird.fr
AF: IRD- Institut de Recherche pour le Developpement, Calle Wimper N32-62 y Coruna, Quito, 17-12-857, Ecuador
AU: Castro, M
EM: mcastro@server.epn.edu.ec
AF: Dept. de Ingenieria Civil y Ambiental, Escuela Politecnica Nacional, Quito, 1701-2759, Ecuador
AU: Hidalgo, X
EM: xhidalgo@server.epn.edu.ec
AF: Dept. de Ingenieria Civil y Ambiental, Escuela Politecnica Nacional, Quito, 1701-2759, Ecuador
AB: Andean alpine glaciers are in rapid retreat, as witnessed by actual measurements, comparative imagery and popular memory. Overall glacier losses will diminish future water availability for human consumption as well as for lahar generation, the product of mixing incandescent eruptive materials with glacial ice and snow. The field study and modeling of long-distance historical lahars from Cotopaxi volcano, Ecuador has shown them to be some of the most voluminous and longest reported. Based on back calculations, peak discharges were commonly between 45,000-60,000 m3/sec, velocities reached 70 km/hr, and run outs attained 325 km. The last "super" debris flow was produced at Cotopaxi in 1877. Observations made after the 1877 eruption reported that the glacier had suffered about 10 meters of ice stripped off the top and the incision of deep gullies from melting and erosion by the scoria block-rich pyroclastic flows. Average reductions of 45% and 60%, respectively, of the area and volume of Cotopaxi´s 19 alpine glaciers during the last 30 years have left an ice cap of only 13 km2 and a volume of 0.60 km3. Descriptions by astute 18th and 19th century observers lead us to conclude that Cotopaxi glaciers were much more robust then, surpassing a total area of about 30 km2, a fact which contributed to generating large volume lahars and high discharges, during the waning "Little Ice Age". If an eruption similar to that of 1877 occurs at Cotopaxi in the future, reduced glacier sizes and the glaciers´ preferential distribution upon the cone will likely attenuate volcano-ice interactions and will lower the probability of "super" lahars being produced during eruptive periods. However, in the last 2000 years of eruptive activity, explosive eruptions display a large size span-- from weakly explosive events (VEI= 2) to highly explosive eruptive cycles (VEI= 4-5). Given the uncertainty of the size of the next explosive eruption of Cotopaxi, several scenarios for lahar generation must be envisioned, which include the magnitude of the explosive event as well as the retreat of the glacier. These scenarios all have implications for the populations living in adjacent valleys, where future lahars may pass.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 8428 Explosive volcanism
DE: 8439 Physics and chemistry of magma bodies
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly