A team of geologists monitored Sabancaya from the settlement of Sallalli on the E flank of the volcano during the daylight hours from 28 April to 10 May. In this period, gas emissions from the active crater fluctuated but were less than those observed in 1998 (BGVN 23:08 and 23:09).

During much of the current visit, a continual background emission was observed rising from the whole crater. Vigorous activity also occurred from three fumaroles located on the S, E, and N rims of the crater. The fumarole on the S rim was most active, with emissions every 1-3 minutes, while the fumarole on the N rim was the most sporadic.

During periods of calm air, gas clouds the width of the crater rose 1,000 m before dissipating, but summit level winds often sheared gas clouds 200-300 m above the vent. Emissions were predominantly white in color, but occasionally were gray or brown and appeared to contain ash. Localized fresh ash deposits were observed on the S flank of the cone. Material was also observed cascading from the ice wall on the E side of the cone forming small talus aprons.

Strong sulfurous smells were noted on five separate days while observers conducted topographic surveys on the lava flows. These coincided with winds blowing downslope from the summit.

While in the town of Arequipa, the group visited the Universidad San Augustin and reviewed the seismic records for Sabancaya and the Colca Valley over the period 1987 to the present. These data failed to reveal any direct correlation between eruptions of Sabancaya and the succession of earthquakes that occurred in the Colca Valley during 1990-1991 (BGVN 16:07).

Frequent seismic swarms have occurred in the Colca Valley around the towns of Lari and Cabana Conde but have shown no correlation with the low level eruptions at Sabancaya. In 1991, the local press (El Correo, 3 May, 1991) reported a correlation between a rise in the geothermal water temperature in the Colca Valley and the activity at Sabancaya but no geophysical data can be provided to support this correlation. Examination of the seismic records for Sabancaya suggests that the magma chamber is isolated.

Geological Summary. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of observed eruptions date back to 1750 CE.

Information Contacts: Mark Bulmer, Center for Earth and Planetary Studies, National Air and Space Museum, Washington DC 20560-0315; Tracy Gregg, Department of Geological Sciences, SUNY Buffalo, NY 14260-3050; Stephen Metzger, Department of Geology, University of Nevada Reno, NV 89557; Steve Schubring, Department of Geography, Geology, and Anthropology, Indiana State University, IN 47802 USA; Jeff Byrnes, Department of Geology and Planetary Sciences, University of Pittsburgh, PA 15260 USA; Guido Salas, Departamento de Geología y Geofísica, Universidad Nacional de San Agustín, Arequipa, Perú.