Mauna Loa (volcano)
Mauna Loa is the largest active volcano in the world, covering nearly half of the island of Hawaii and accounting for about 85% of the land mass within the Hawaiian archipelago. Standing approximately 13,100 feet (3,993 meters) above sea level and extending another 16,400 feet (4,999 meters) below the ocean's surface, the volcano's total height is around 55,700 feet (16,977 meters). It is classified as a shield volcano due to its gently sloping sides formed by fluid basaltic lava flows, which result in non-explosive eruptions that can still pose significant hazards. Since scientific records began in 1843, Mauna Loa has erupted thirty-three times, with its most notable eruptions occurring in 1950 and 1984, the latter coming dangerously close to populated areas. The volcano's activity can lead to dangerous lava flows and volcanic gases, contributing to air quality issues known as "vog." Furthermore, Mauna Loa's eruptions have been linked to substantial earthquakes, including a devastating one in 1868. Despite these dangers, Mauna Loa is also a site for limited recreational hiking, attracting experienced trekkers who must be wary of the challenges posed by the altitude and terrain. Scientists continue to monitor the volcano closely, especially after signs of increased seismic activity were noted in 2015, indicating that another eruption may occur in the future.
On this Page
Subject Terms
Mauna Loa (volcano)
Mauna Loa is the world's largest active volcano. It is so large that it covers about half the island of Hawaii and makes up about 85 percent of the total land mass of all the islands that are part of the Hawaiian Island chain. It has erupted thirty-three times since accurate scientific records of its activity began in 1843, and the 1984 eruption threatened the largest populated area on the island. On average, Mauna Loa has erupted every five years over the last three thousand years. In 2015, scientists noticed signs of an impending new eruption.
Background
Volcanoes are openings in Earth's crust that allow hot gas, vapor, rocks, and molten rock called magma to escape from below the surface during events called eruptions. Once magma reaches the surface, it is known as lava. Each time a volcano erupts, lava and other materials pile up around the vent. In time, they form a mound around the vent that can become a mountain.
The Hawaiian Islands formed over a hotspot, a place where magma flows freely from below the tectonic plates that make up the base of Earth's surface. As magma flowed from this hotspot and cooled, it resulted in a formation known as a seamount, or an underwater mountain made of lava. The hotspot also created volcanoes. The eight major islands and many other minor islands and formations that make up Hawaii all were formed by volcanic activity.
Not all volcanic lava is the same. The lava that flows throughout the Hawaiian Islands is made mostly of basalt. Basalt becomes very fluid when it melts and flows relatively smoothly. As a result, Hawaiian volcanoes do not usually erupt explosively or blast huge amounts of fiery rock and ash into the air. Instead, eruptions usually involve lava flows, which occur when hot melted rock pours over the side of a volcano, much like water boiling over the sides of a pot. The thin, fluid lava moves quickly downhill away from the caldera, or the area of the volcano where the lava exits. As a result, the lava does not have a chance to cool and build up. Instead, the lava flows some distance away before it cools and hardens. This process forms gently sloping mountainsides rather than high, conical ones. These types of volcanoes are called shield volcanoes because their sloping sides are made up of many fluid lava flows that create a smooth, domed appearance, similar to a shield. The Hawaiian Islands, including Mauna Loa, are considered shield volcanoes.
Overview
Scientists believe Mauna Loa began forming between six hundred thousand and one million years ago. It stands about 13,100 feet (3,993 meters) above sea level and descends under the ocean's surface another 16,400 feet (4,999 meters). Mauna Loa is so large and heavy, however, that its weight creates a 26,200-foot (7,985-meter) depression in the ocean floor. In all, the volcano stretches about 55,700 feet (16,977 meters) from its base in the depression on the ocean floor to its peak.
The name Mauna Loa means "long mountain" in the native language. The part of Mauna Loa above water has a width of about 74 miles (119 kilometers). It is the largest active volcano on Earth and is among the planet's most active volcanoes overall.
Even though Mauna Loa does not erupt with explosive blasts of lava and ash that spray into the air, it is still dangerous. There have been eight instances since recordkeeping began when lava flows from Mauna Loa were so large that they stretched from the caldera all the way to the sea. The flows are usually accompanied by a phenomenon called a "curtain of fire," during which fire shoots from vents in the volcano. The curtain of fire is followed by scorching hot lava flows that range in temperature from 1,165 to 1,600 degrees Fahrenheit (629 to 871 degrees Celsius). These lava flows destroy towns and forests and ruin crops and ranches. In addition, volcanic flows in Hawaii are accompanied by a heavy fog that local residents call "vog." This fog, made of sulfur dioxide and other materials along with water vapor, can kill crops and speed up the rusting of metal. It can be dangerous to animals and people with respiratory ailments.
Mauna Loa's eruptions have been responsible for triggering earthquakes. An 1868 eruption caused an earthquake estimated to have reached a magnitude of 8.0 and created deadly landslides. The earthquake caused a tsunami that killed seventy-nine people. Other earthquakes caused by Mauna Loa have caused significant infrastructure damage to roads and bridges miles away from the lava flow. Significant eruptions occurred in 1950, when the volcano released an estimated 16.2 billion cubic feet (460 million cubic meters) of basaltic lava over twenty-three days, and in 1984, when the flow came within 4 miles (6.4 kilometers) of Hilo, the most populated area of the island.
Although the volcano can pose a devastating threat to the island of Hawaii and its inhabitants, it is also the site of a national park. Limited numbers of experienced hikers and wilderness trekkers are allowed to climb and stay on the volcano for three nights at a time. In addition to the threats inherent to climbing an active volcano, Mauna Loa reaches altitudes high enough to cause altitude sickness, which can be fatal. It is a relatively strenuous climb during which temperatures can reach levels low enough to cause hypothermia, or low body temperature. The broken glass–like sharpness of the hardened basaltic lava increases the risk of life-threatening cuts resulting from falls.
In 2015, researchers noted an increase in the amount of seismic activity and earthquakes in the area of Mauna Loa, a possible sign of an impending eruption. Island residents, many of whom may not remember the previous eruption in 1984, were advised to monitor official sources and be alert for a potential threat. Scientists have said that while they cannot say when Mauna Loa will erupt or which direction the flow will go, they do know that it will erupt again.
Bibliography
Boneza, Jenn. "New Sensors Will Help Monitor Activity as Scientists Say Mauna Loa 'Will Erupt Again.'" KHON2 Honolulu News, 13 Sept. 2017, khon2.com/2017/09/13/new-sensors-will-help-monitor-activity-as-scientists-say-mauna-loa-will-erupt-again/. Accessed 13 Sept. 2017.
Bracken, Sherry. "Mauna Loa Alert Still in Effect." Hawaii Public Radio,13 Sept. 2017, hpr2.org/post/mauna-loa-alert-still-effect. Accessed 13 Sept. 2017.
"How Did the Hawaiian Islands Form?" National Oceanic and Atmospheric Administration, oceanservice.noaa.gov/facts/hawaii.html. Accessed 13 Sept. 2017.
"Mauna Loa." United States Geological Survey, volcanoes.usgs.gov/volcanoes/mauna‗loa/. Accessed 13 Sept. 2017.
"Mauna Loa." United States National Park Service,www.nps.gov/havo/planyourvisit/hike‗maunaloa.htm. Accessed 13 Sept. 2017.
"Mauna Loa Volcano." Hawaii Center for Volcanology, University of Hawaii,www.soest.hawaii.edu/GG/HCV/maunaloa.html. Accessed 13 Sept. 2017.
"Shield Volcanoes." Volcano World, Oregon State University,volcano.oregonstate.edu/shield-volcanoes. Accessed 13 Sept. 2017.
Sprinkles, Karen. "What Kind of Damage Has Mauna Loa Caused?" USA Today,traveltips.usatoday.com/kind-damage-mauna-loa-caused-62501.html. Accessed 13 Sept. 2017.