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An under-appreciated and poorly understood aspect of Mauna Loa's eruptive activity is the presence of explosion debris on the east and west sides of the summit caldera.
Rocks ejected during explosive event at summit Mauna Loa Volcano, Hawai‘i
An under-appreciated and poorly understood aspect of Mauna Loa's eruptive activity is the presence of explosion debris on the east and west sides of the summit caldera. The blocks shown in the photos were ejected sometime during or after the caldera formed, less than 1,300 years ago. The largest blocks are more than 1.5 m in diameter. Most consist of pieces of old lava flows, but some blocks on the west side are coarse grained (gabbro is the official rock name) and probably came from intrusions that cooled slowly enough for minerals to grow large. The blocks were hot when hurled from the caldera, as can be determined by the pattern of cooling cracks within the blocks.
Ground and surface water heated to steam is thought to be responsible for many of the explosions at Mauna Loa's lower neighbor, Kīlauea. But, Mauna Loa stands so high that it is hard to imagine that much water was available. Could there have been buried ice lenses large enough to have powered the explosions? Could large snow banks have supplied the water? Or, could the explosions have been driven by carbon dioxide or other gases derived from magma? Much research remains to be done before these questions can be answered. Meanwhile, explosions should be viewed as an infrequent, but nonetheless present, hazard at the top of Earth's largest volcano.
