HVO reported on 27 January that during the previous couple of months the rate of lengthening across Mauna Loa's summit caldera (Mokuʻāweoweo) slowed significantly. The lengthening started in late April or May, as did uplift measured by GPS and ground tilt measured by several dry-tilt stations. As of the 27th, seismicity remained at low levels.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

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 Mokuʻāweoweo summit is caldera, which is within an older and larger 6 x 8 km caldera. Two large debris avalanches traveled nearly 100 km; 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 Mokuʻāweoweo caldera until the present, an additional 25% of the volcano has been covered with lava flows, mainly from summit and NW rift zone vents.