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Report on Mauna Loa (United States) — 14 May-20 May 2003

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 May-20 May 2003
Managing Editor: Gari Mayberry

Please cite this report as:

Global Volcanism Program, 2003. Report on Mauna Loa (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 14 May-20 May 2003. Smithsonian Institution and US Geological Survey.

Volcano Profile |  Weekly Report (14 May-20 May 2003)


Mauna Loa

United States

19.475°N, 155.608°W; summit elev. 4170 m

All times are local (unless otherwise noted)


HVO reported on 18 May that inflation may have resumed at Mauna Loa's summit during the week, after slackening off following an increase in mid-February. Seismicity, however, remained low. Inflation was noted where the GPS network first showed definite lengthening of the lines across the summit caldera in late April or May 2002, after nearly 10 years of slight deflation. HVO interpreted the lengthening, uplift, and tilting to indicate resumed swelling of the magma reservoir within the volcano.

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.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)