Apparent ash plumes from Mt. Siple were detected by NOAA 10 satellite imagery (visible band, orbit 10406) on 18 September at 1301 and again on 4 October at 1534 (infrared and visible bands, orbit 10636). The 4 October plume extended ~160-170 km WNW and was well-defined, but it was uncertain whether the plume originated from the volcano's summit or base [but see 13:12]. A review of past LANDSAT images indicated a possible February 1988 ash deposit on the ice near the volcano. Michael Matson and George Stephens are currently applying additional satellite data aquisition and reduction techniques to refine these interpretations.

. . . Geologists hope to visit the volcano in November.

Geological Summary. Mount Siple is a shield volcano that forms an island along the Pacific Ocean coast of Antarctica's Marie Byrd Land. The massive 1,800 km3 volcano is truncated by a 4-5 km summit caldera and is ringed by tuff cones at sea level. A possible eruption cloud observed on satellite images on 18 September and 4 October 1988 was considered to result from atmospheric effects, after low-level aerial observations revealed no evidence of recent eruptions. Trachytic rocks at the summit have been Ar-Ar dated to about 227,000 and 169,000 years old.

Information Contacts: W. Gould, M. Matson, and G. Stephens, NOAA; W. LeMasurier, Univ of Colorado.