Mauna Loa is an active shield volcano that is located on the island of Hawaii and is one of five volcanoes that form the island. It reaches an elevation of 13,679 feet, slightly shorter than Mauna Kea, but it is still considered one of the volcanoes on Earth due to its length and depth. Its name means Long Mountain in the Hawaiian language. This volcano is thought to have emerged from the ocean about 400,000 years ago and has most likely been active for 700,000 years. It was created in the same manner as all Hawaiian volcanoes, when the Pacific tectonic plate moved over the Hawaiian hotspot. Its most recent eruption occurred in 1984 and it has been placed on the list of Decade Volcanoes.
Mauna Loa extends across an area that is 2,035 square miles in length and 75 miles in width and comprises more than half of the entire island of Hawaii. As is typical to shield volcano, this volcano holds a long broad dome that is comprised of tholeiitic basalts that accumulated during its shield stage, which is thought to be coming to an end. Its summit holds two rift zones that are covered with recent lava flows, as well as cinder cones and splatter cones.
The lava flows from Mauna Loa interact with those of nearby volcanoes, especially Kīlauea, which was once thought to be part of it. Mauna Loa is sagging into Kīlauea along its southwestern rift, causing Kīlauea to move east at rate of four inches each year. This has caused many past earthquakes and the creation of a debris field known as Hilina Slump. It has displayed a cycle of activity that switches from the summit for a few hundred years to rift zones for a few centuries. Two of these cycles have been recorded lasting between 1,500 and 2,000 years each. Mauna Loa is the only volcano in Hawaii that displays this cyclical behavior.
Although ancient Hawaiians have lived on the island for about 1,500 years, there are very few records regarding volcanic eruptions. The records that do exist date back to the eighteenth and nineteenth centuries and it is thought that eruptions occurred in 1730 and 1750 and possibly around 1780 or 1803. The first accepted record of eruption dates to 1843 and the volcano has produced thirty-two eruptions since that date. These eruptions have been typical to other Hawaiian eruptions, displaying slow but heavy lava flows that are followed by flank eruptions that last a few months. Some of these include the 1855 eruption, which produced large lava flows, and the 1935 eruption, which was disputably stopped by bombs. Other noteworthy eruptions occurred in 1942, months after WW II began, and in 1950, producing lava flows that reached into the sea for fifteen miles in only three hours. Its last eruption occurred in 1975, although this was only a minor eruption.
Mauna Loa was first climbed by ancient inhabitants, but the first outsider to reach its summit was Archibald Menzies and his team of three others. The team, which made the climb in 1791, was assisted by King Kamehameha I, who told them an easier route to reach the summit after their first two attempts. The team as surprised to find snow covering the summit and experienced cold morning temperatures. Today, the highest elevations on the volcano experience cold temperatures while lower elevations hold tropical climates that support dense forests. The summit provides a good atmosphere for observatories that monitor events in the earth’s atmosphere and in space. The United States Geological Survey lists this volcano as a level one hazard, because of its history of violent eruptions.
Image Caption: Mauna Loa Volcano towers nearly 3,000 m above the much smaller Kilauea Volcano (caldera in left center). Credit: J.D. Griggs/Wikipedia