18 US Volcanoes as ‘Very High Threat’ (Kilauea #1)

Your Favorite Volcanos Are Beautiful… And (Very) Dangerous: Kilauea is the most dangerous volcano in the United States. Mauna Loa is #16. Not to be left out, Hualalai comes in at #23.

USGS scientists have classified 18 U.S. volcanoes as “very high threat”  because of what’s been happening inside them and how close they are to people. The U.S. Geological Survey has updated its volcano threat assessments for the first time since 2005. To produce the rankings, the USGS uses a 24-factor hazard and exposure matrix, assessing explosive activity in the past 500 and 5,000 years, frequency of eruptions, and the level of impact an eruption could have on local populations, airplanes, transportation, and power infrastructure.

Kilauea is the most active volcano in the United States “and it’s got a lot of development right on its flanks,” said government volcanologist John Ewert, the report’s chief author. He said Hilo, Hawaii, is probably the biggest city in the United States in a hazard area for a very high threat volcano, Mauna Loa.

The U.S. Geological Survey has updated its volcano threat assessments for the first time since 2005. The top five volcanic danger list:

  • Kilauea – Hawaii
  • Mount St. Helens – Washington
  • Mount Rainier – Washington
  • Redoubt Volcano – Alaska
  • Mount Shasta – California

Besides the top 5, the rest of the Big 18 are Mount Hood, Three Sisters and Crater Lake in Oregon; Akutan Island, Makushin, Mount Spurr and Augustine in Alaska; Lassen and Long Valley in California; Mount Baker and Glacier Peak in Washington; and Mauna Loa in Hawaii.

The U.S. Geological Survey has these  volcanoes at the top of their danger list:

With regards to Mauna Loa, Kilauea is the most active volcano in the United States “and it’s got a lot of development right on its flanks,” said government volcanologist John Ewert, the report’s chief author. He said Hilo, Hawaii, is probably the biggest city in the United States in a hazard area for a very high threat volcano, Mauna Loa. Eleven of the 18 at-risk volcanoes are located in Washington, Oregon, or California.

From the Hawaii Volcanoes National Park website:

How many volcanoes are there on the Big Island? Which ones are extinct, dormant, or active? Five volcanoes make up the island of Hawai`i: Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea.

Kohala, the oldest volcano on this island, last erupted about 60,000 years ago and is considered extinct. Mauna Kea last erupted 3,600 years ago and is dormant. Hualalai, Mauna Loa, and Kilauea are active.

Hualalai erupted seven times in the last 2,100 years. The only historical eruptions were in 1800 and 1801. Mauna Loa last erupted in 1984 and sent flows towards Hilo. Kilauea has been erupting since 1983.

Loihi, a submarine volcano, is 15 miles (24 km) southeast of the island and 3,178 feet (969 m) below sea level. Loihi will probably not reach sea level before 250,000 years or more. Seismicity, geothermal vents, and fresh lava indicate Loihi is active.

Where does the lava come from? Rocks that are moving upward in the mantle beneath Hawai`i begin to melt about 40 to 60 miles (60 to 100 km) depth. The molten rock, called magma, rises because of its relatively low density. The magma “ponds” in a reservoir 1 to 4 miles (2 to 6 km) beneath the summit. The magma can follow fractures up to the crater and produce a summit eruption. During the current eruption, the magma has followed a zone of weakness, the East Rift Zone. Magma reaches the surface at a vent, an opening at the surface through which volcanic material is extruded. There have been several vents during the last 10 years. The currently active vent is 15 miles (24 km) from the summit and 6 miles (9.6 km) above the coast.

Where does the lava come from? How long did it take for the lava to move down the lava tube system from the vent to the ocean? How much heat is lost as the lava moves from the vent to the ocean? How large are the lava tubes feeding the coastal flow (how long and what diameter)? How thick is the crust over the lava tube (and under my feet)?

Lava is supplied in lava tubes that extend from vents on the flank of the Pu`u `O`o cone down to the ocean. A skylight (collapsed roof of the tube) provides a view into a lava tube.

The lava originates by melting in the mantle 40 miles (60 km) below the surface. The liquid rock below the surface is called magma. The magma rises through conduits to a reservoir a couple of miles beneath the summit of Kilauea. From there, the magma travels through a dike that extends from the summit down into the flank of the volcano. The magma rises from the dike up to the vents at the surface. From the vents down to the coast, the lava is transported in tubes. It takes about 3 hours for the lava to move down the lava tube from the vent to the ocean. The temperature of the lava drops about 14F (8C) as it moves from the vent to the ocean. The first crust forms on the lava at about 930F (500C). The lava tubes are about 6 miles (9.6 km) long and have a diameter of 12 to 15 feet (4 to 5 m – up on the pali). Tubes on the coast are 3 to 6 feet (1-2 m) below the surface, about 3 feet (1 m) in height, and up to 30 feet (10 m) in width. The tubes are usually a few feet below the surface.