No changes have been noted by HVO at Mauna Loa through 21 September. Since early July 2004, an increasing number of earthquakes has been recorded from beneath Mauna Loa. From week to week the numbers fluctuate but remain well above the earlier established norm. Through the second week of September, more than 500 earthquakes were centered beneath the summit caldera and the adjacent part of the southwest rift zone. Most of these earthquakes were quite deep, 35-50 km below the surface, and less than M 3. Inflation was continuing at the summit and has so far shown no change during the increased seismic activity.

Geological Summary. Massive Mauna Loa is a basaltic shield volcano that rises almost 9 km from the ocean floor to form the world's largest Holocene volcano. Flank eruptions typically occur from the lengthy NE and SW rift zones, and from the Moku'aweoweo summit is caldera, which is 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 volcano is covered by lavas less than 4,000 years old (Lockwood and Lipman, 1987). Beginning about 1,500 years ago, a series of voluminous overflows from a summit lava lake covered about 25% of the volcano's surface. Over the last 750 years, from shortly after the formation of Moku'aweoweo caldera until the present, an additional 25% of the volcano has been covered with lava flows, mainly from summit and NW rift zone vents.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)