Mauna Loa - World's Largest Active Volcano

The word volcano comes from Vulcan, the Fire God of the ancient Romans. Most of us associate volcanic eruptions with mountains. However, mountain volcanoes are only one of many types of volcanoes, as their structure and behavior are governed by a number of factors. Some volcanoes may be large plateaus and others may be submarine volcanoes located on the ocean floor. Volcanoes are generally found over diverging or converging tectonic plates. Volcanoes can also form where the Earth's crust is stretched or thin.

A volcanic eruption is the result of the build up of pressure below the surface or the Earth. The hot, molten rock, ash, and gases push through the surface of the Earth, causing fissures or cracks to appear.

Mauna Loa is a shield volcano located on the island of Hawaii. Mauna Loa, which means Long Mountain in Hawaiian, rises to the height of 13,680 ft. above sea level. Scientists and geologists estimate that Mauna Loa began erupting between 700,000 to 1,000,000 years ago and has continued since. Mauna Loa, the largest (area wise) volcano on Earth, is 60 miles long and 30 miles wide. It is shaped like a shield, with gently sloping sides because its lava is extremely fluid (it has low viscosity).

Magma chambers below the surface of the mountain are the source of its activity. This magma comes from the Hawaii hotspot, which the creation of the Hawaiian island chain has been accredited to. Mauna Loa eruptions are rarely violent, and usually in the form of lava flows fed by lava fountains. A lava flow is a transient outpouring of lava, and is created during a non-explosive effusive eruption.

Most of its eruptions have occurred in three regions on the mountain: at the summit and in two rift zones extending northeast and southwest of the summit. The mountain's summit caldera is called Mokuaweoweo which is 1.75 to 3 miles in diameter. It is estimated that the caldera was formed 1,000 -1,500 years ago as the outcome of a very large eruption from the northeast rift zone. It emptied out the shallow magma chamber beneath the summit, which eventually collapsed.

The natives of Hawaii have witnessed eruptions for many centuries. However, there is written documentation only about the eruptions of Mauna Loa that have occurred since the early 1800s. The first recorded eruption occurred in 1843, and since then 33 eruptions have been recorded. Two eruptions of Mauna Loa have caused a significant amount of destruction. One took place in 1926, when the village of Hoʻōpūloa Makai was overrun by lava flows. The other that took place in 1950, was the largest witnessed from the mountain and sent lava flows racing towards the sea. The village of Hoʻokena Mauka was destroyed on June 2, 1950 by these advancing flows. Another significant eruption took place in 1935, but damage was contained. While the lava flows were large and threatened the village of Hilo, the use of ammunition was made to avert tragedy. Five bombers of the 23rd and 72nd Bombardment Squadrons of the United States Air Force dropped bombs ahead of the lava in order to divert it away from Hilo.

Mauna Loa's most recent eruption occurred from March 24, 1984 and lasted till April 15, 1984. Since then the mountain has been dormant. The main volcanic hazard Mauna Loa presents are lava flows. However, most flows advance slowly at about walking pace and are hardly a threat to human life. The sudden massive collapse of the volcano's flanks are a greater hazard, but this is a rare possibility. Mauna Loa has been intensively monitored by the Hawaiian Volcano Observatory (HVO) since 1912.

The slow drift of the Pacific Plate will eventually carry the volcano away from the hotspot. This will happen within 500,000 to one million years from now, by when the volcano will become extinct.