Volcano Watch: Deciphering explosive behavior at Mauna Loa

Map of explosive deposits at the edge of Moku‘āweoweo, the summit caldera of Mauna Loa. Map showing the size distribution of ejecta, sorted by maximum length in centimeters (one inch is about 2.5 cm). The colors indicate the different size fractions in centimeters. The largest blocks were found closest to the rim. In general, clast size diminished with increasing distance, but medium-sized blocks were found nearly at the distal extent of fan limits. The dark flows in the image outside the caldera are the youngest ‘a‘a flows. (USGS map/Special to West Hawaii Today)

Types of explosive clasts found in the debris fan deposits at the summit of Mauna Loa: (A) unaltered ponded lava flow, (B) unaltered pāhoehoe, (C) altered ponded lava flow, often has a red to pink hue, (D) thermally altered pāhoehoe, often has a red-to-pink hue, (E) gabbroic xenolith, the most crystalline rocks we found, (F) bread-crust outer surfaces and vesicular interiors or dense clasts with crackle or crazed surface rinds, (G) bread-crust due to quenching. (USGS photos/Special to West Hawaii Today)

Mauna Loa is known for its effusive eruptions that produce spectacular lava flows. However, some of the volcanic products found on Mauna Loa are pyroclastic or explosive in character.