Report on Mauna Loa (United States) — 9 October-15 October 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 October-15 October 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Mauna Loa (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 9 October-15 October 2002. Smithsonian Institution and US Geological Survey.
19.475°N, 155.608°W; summit elev. 4170 m
All times are local (unless otherwise noted)
A brief period of low-amplitude tremor occurred at Mauna Loa's summit on 7 October, lasting several minutes. It apparently was triggered by, or at least quickly followed, a small earthquake. The following day, several more small earthquakes took place. By the 10th, seismicity had returned to low levels. During 8-15 October, the permanent continuous global positioning system network indicated that ongoing lengthening occurred across Moku`aweoweo summit caldera as it has since late April or May.
Geologic Background. Massive Mauna Loa shield volcano rises almost 9 km above the sea floor to form the world's largest active volcano. Flank eruptions are predominately from the lengthy NE and SW rift zones, and the summit is cut by the Mokuaweoweo caldera, which sits within an older and larger 6 x 8 km caldera. Two of the youngest large debris avalanches documented in Hawaii traveled nearly 100 km from Mauna Loa; the second of the Alika avalanches was emplaced about 105,000 years ago (Moore et al. 1989). Almost 90% of the surface of the basaltic shield volcano is covered by lavas less than 4000 years old (Lockwood and Lipman, 1987). During a 750-year eruptive period beginning about 1500 years ago, a series of voluminous overflows from a summit lava lake covered about one fourth of the volcano's surface. The ensuing 750-year period, from shortly after the formation of Mokuaweoweo caldera until the present, saw an additional quarter of the volcano covered with lava flows predominately from summit and NW rift zone vents.