Report on Karthala (Comoros) — 20 August-26 August 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 August-26 August 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Karthala (Comoros). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 20 August-26 August 2003. Smithsonian Institution and US Geological Survey.
11.75°S, 43.38°E; summit elev. 2361 m
All times are local (unless otherwise noted)
According to news reports, Observatoire Volcanologique du Karthala scientists noted a steady increase in seismicity at Karthala over the past 3 months. Around 100 earthquakes occurred per day in August in comparison to 1-2 per day in June.
Geologic Background. The southernmost and largest of the two shield volcanoes forming Grand Comore Island (also known as Ngazidja Island), Karthala contains a 3 x 4 km summit caldera generated by repeated collapse. Elongated rift zones extend to the NNW and SE from the summit of the Hawaiian-style basaltic shield, which has an asymmetrical profile that is steeper to the S. The lower SE rift zone forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera. More than twenty eruptions have been recorded since the 19th century from the summit caldera and vents on the N and S flanks. Many lava flows have reached the sea on both sides of the island. An 1860 lava flow from the summit caldera traveled ~13 km to the NW, reaching the W coast to the N of the capital city of Moroni.