Earlier this spring, the summit of Hawaii's Kilauea volcano exploded for the first time since 1924. The blast was first thought to be an earthquake, but volcanologists quickly realized that gases bottled up beneath a vent named "Halema`uma`u" had burst forth, spewing debris over an area of 75 acres. Parts of Hawaii Volcanoes National Park were forced to close when sulfur dioxide levels became deadly.

Mount Kilauea is an active shield volcano in the Hawaiian Islands, one of five shield volcanoes that together form the Island of Hawaii. Kilauea rises 4,091 feet above sea level and appears as only a bulge on the southeastern flank of the much taller (13,677 feet) Mauna Loa.

For many years, Kilauea was thought to be a mere satellite of its giant neighbor, not a separate volcano. However, research over the past few decades shows clearly that Kilauea has its own magma-plumbing system, extending to the surface from more than 30 miles deep in the earth.

Shield volcanoes have broad, gentle slopes that are built by the eruption of fluid basalt lava. The 2000-degree lava flows out of the volcano in all directions from a central summit vent or group of vents, building a broad, gently sloping profile, much like that of a warrior's shield. The largest volcanoes on Earth are shield volcanoes, and one of the largest known volcanoes in our solar system, Olympus Mons on Mars, is also a shield volcano.

On an average day, Kilauea puts out several hundred thousand cubic yards of lava, much of which makes its way into the ocean. The volcano also causes frequent earthquakes, at least once a week. However, many of them are so small that only a few people feel them.

Kilauea ranks among the world's most active volcanoes, erupting 62 times in 245 years. The current eruption began in 1983 and has been going on since.

-- By Dan Malerbo, Buhl Planetarium and Observatory