Multi-Hazard Mitigation Plan: 08. Lava And Vog

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Chapter 8:Hazard Analysis—Lava and VOG CHAPTER 8 - LAVA FLOWS, VOLCANIC GAS, AND ASHFALL 8.1 Hazard Description 8.1.1 Lavallolcanoes The Island of Hawaii is composed of five volcanoes,two of which(Mauna Loa and Kilauea) have been very active in the past 100 years and pose the most immediate threat to life and property. A third volcano, Hualalai, last erupted in 1801 and has the potential to erupt again within our lifetime. Mauna Kea last erupted approximately 3,500 years ago. Kohala, considered extinct, is the oldest volcano on the island and last erupted approximately 60,000 years ago. Most of the eruptions of Hawaiian volcanoes are not explosive(therefore ash fall is not a ma- jor concern) and are characterized by relatively quiet outflow of very fluid lava. These erup- tions, however, can still be quite hazardous because they may be erupted in huge volumes, and on steeper slopes, the fluid lava can rapidly travel many miles from its source.33 Lava flows present potential threats to homes, infrastructure, natural and historic resources and entire communities. The areas exposed to the highest risk from lava flows are those situated downslope and in close proximity to the active rift zones of Mauna Loa and Kilauea. Steep slopes may allow lava flows to move quickly from the summit to the ocean in a matter of hours. Besides the direct threat of inundation, lava flows may also cut across a community's single roadway escape route limiting the amount of time available for evacuation. The following briefly profiles the volcanoes that pose potential hazards. • Mauna Loa, like most Hawaiian volcanoes, has a summit caldera and two radiating rift or fracture zones. Comprising approximately 50% of the island of Hawaii,Mauna Loa poses a lava hazard threat to the districts of South Hilo, Puna, Ka'u, South Kona,North Kona and South Kohala. Mauna Loa eruptions can occur at the summit, from vents on the southwest rift zone and the east rift zone and on the north and northwest flanks of the volcano. • Kilauea is one of the world's most active volcanoes and over 90% of its surface is covered by lava less than 1,100 years old. All of Kilauea's eruptions have occurred either at its summit, or along one of two rift zones that extend from the summit to the coastline on the east and southwest flanks of the volcanoes. Eruptions on the east flank of Kilauea are a threat to portions of the Puna district. Eruptions on the southwest flank of Kilauea are a threat to land within the Hawai'i Volcanoes National Park and the district of Ka'u. • Hualalai is much older than Kilauea and Mauna Loa and has not erupted since 1800-1801. Eruption activity on Hualalai has been far less frequent with 25% of the volcano covered by flows less than 1,000 years old. Hualalai has erupted near its summit, along the northwest and south-southeast rift zones and from vents on the north flank of the volcano. Eruptions on Hualalai threaten land within the North Kona district. 33 USGS Fact Sheet 074-97. 8-1 Hawaii County Multi-Hazard Mitigation Plan