Volcano Watch — Lava Inundation Zones Identified for Mauna Loa

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Mauna Loa will undoubtedly erupt again. When it does, one critical question is, Which areas are threatened with inundation? Researchers at HVO have produced maps that will help Civil Defense in the event of the next eruption of Mauna Loa. The map production was sponsored by the U.S. Geological Survey and the County of Hawai`i, with funds provided by the Federal Emergency Management Administration's Project Impact.

Mauna Loa has a summit caldera and two rift zones. The two rift zones-elongate fracture systems-extend to the northeast and southwest from the summit. Most of Mauna Loa's eruptive fissures and vents are located at the summit and along the rift zones. A number of vents, however, lie outside these areas and occur along fissures that are oriented radially to the summit area; these are called radial vents.

Mauna Loa's summit caldera provides a topographic barrier that protects an area to the southeast from lava flows. The summit caldera also provides a topographic barrier for an area west of the caldera, but this protection is negated by the presence of radial vents on this flank. Radial vents are absent east of the caldera.

Geologic mapping of the surface lava flows of Mauna Loa has helped us identify more than 500 flows originating from the summit area, rift zones, or radial vents. These past flows delineate the approximate pathways of future flows that originate in the same or similar locations. The mapped lava flows were used to construct nine maps depicting 18 inundation zones on Mauna Loa. Each zone reflects a segment of the volcano that could send flows in its direction. Thus, the inundation-zone maps show an area on the flank of Mauna Loa that could potentially be covered by future eruptions originating from the summit, rift zones, and radial vents. Although any part of an inundation zone could potentially be overwhelmed by a future eruption, it is more likely that only part of a zone would be buried in a single eruption.

The inundation maps were constructed to assist emergency managers and decision makers during an eruption. Accurate estimates of areas that could be affected by lava flows pouring from specific parts of Mauna Loa are critical for Hawai`i County. So they can quickly warn people and develop plans to deal with the crisis. The maps allow decision makers to quickly identify communities, infrastructure, and roads between the coast and possible vent locations.

When an eruption starts, the maps will allow emergency managers to identify the plausible downslope areas likely to be impacted and decide how to deploy resources to cope with the event. The maps are intended to make asset allocation more efficient and effective. Although the intent of these maps is to facilitate emergency response activities, they can also be used by the public to educate themselves as to which segment of the rift zone or summit can erupt flows into their region and take the appropriate action if lava flow inundation becomes imminent.

We recognize that many more homes, small communities, and facilities are scattered around the slopes of Mauna Loa than are explicitly identified in the 18 inundation zone maps. We caution individuals whose homes, communities, and facilities are not specifically identified by inundation zones on the maps to expect lava flow hazards at least at the same level as the communities and facilities that do appear on the maps (Wright and others, 1992).

The inundation zones identified on the nine maps are (1) Kaumana, Waiakea and Volcano-Mountain View; (2) Kapapala; (3) Pahala, Punalu`u, and Wood Valley; (4) Na`alehu; (5) Ka Lae; (6) Hawaiʻian Ocean View Estates (HOVE), Kapu`a, and Miloli`i; (7) Ho`okena, Ka`ohe, and Ka`apuna; (8) Honaunau and Kealakekua and (9) Puako. The names given are descriptive and are meant to represent the larger geographic regions. The maps are at several scales, from 1:50,000 to 1:95,000.

Volcano Activity Update

Eruptive activity at the Pu`u `O`o vent of Kīlauea Volcano continued unabated during the past week. Streams of lava are visible on Pulama pali and Paliuli. The lava breaks out of the main Mother's Day tube above Pulama pali and wends it way to the coastal flat in a series of open channels and tubes. Surface breakouts are also found in interior areas of the Kohola flow, and the National Park Service has marked a trail out to the closest activity. Ocean entry activity at the West Highcastle delta was weak to nonexistent during the week.

The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The steam clouds are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary and onto the lava deltas and benches.

Three earthquakes were reported felt during the past week. Two small earthquakes were felt by a resident of Leilani Estates at 2:11 a.m. and 2:14 a.m. on May 6. They had magnitudes of 1.6 and 1.8, respectively. Both earthquakes were located 3-4 km (2 mi) east of Pu`ulena Crater at a shallow depth. At 6:55 a.m. on Wednesday, May 7, a resident of Volcano felt an earthquake. The magnitude-2.6 temblor was located 13.3 km (8 mi) south of Volcano at a depth of 9.1 km (5.5 mi).

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity remains low with only 2 earthquakes located in the summit area during the last seven days.