An ASTER satellite image from 23 September showed a 3.5-km-long lava flow extending from the summit of Montagu Island (Mt. Belinda) into the sea. This was the largest effusive event observed during the 4-year-old eruption. Based on MODVOLC alerts, the flow appeared to have started sometime between 10 and 14 September. A conspicuous 90-m-wide channel was visible ~1 km from the vent. The image also showed a steam plume at the location of the ocean entry, and an ash-rich plume extending NE from the volcano's summit.

Geological Summary. The largest of the South Sandwich Islands, Montagu consists of a massive shield volcano cut by a 6-km-wide ice-filled summit caldera. The summit of the 11 x 15 km island rises about 3,000 m from the sea floor between Bristol and Saunders Islands. Around 90% of the island is ice-covered; glaciers extending to the sea typically form vertical ice cliffs. The name Mount Belinda has been applied both to the high point at the southern end of the summit caldera and to the young central cone. Mount Oceanite, an isolated peak at the SE tip of the island, was the source of lava flows exposed at Mathias Point and Allen Point. There was no record of Holocene activity until MODIS satellite data, beginning in late 2001, revealed thermal anomalies consistent with lava lake activity. Apparent plumes and single anomalous pixels were observed intermittently on AVHRR images from March 1995 to February 1998, possibly indicating earlier volcanic activity.

Sources: Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts Team, British Antarctic Survey