Mauna Loa

Mauna Loa is a massive shield volcano located on the Island of Hawaiʻi in the Pacific Ocean.

It is recognized as the largest active volcano on Earth by both mass and volume. While the submarine Tamu Massif is larger, Mauna Loa remains a dominant geological force. It is a shield volcano, which means it has a broad, dome-like shape with gentle slopes. These slopes are typically only about 12 degrees at their steepest points. This specific shape is a direct result of the lava being extremely fluid.

The volcano grows through a specific geological process involving a mantle plume. This plume is often called a hotspot, which is a stationary source of heat deep within the Earth's mantle. As the Pacific Plate moves slowly over this hotspot, magma rises to the surface to create volcanoes. This process has formed the Hawaiian–Emperor seamount chain over the last 70 million years. Mauna Loa likely began erupting at least 700,000 years ago. It probably emerged above sea level approximately 400,000 years ago through a series of surtseyan eruptions.

Mauna Loa's structure is defined by its enormous scale and its summit features. The volcano consists of approximately 18,000 cubic miles of solid rock. This massive amount of material makes up more than half of the surface area of Hawaiʻi. If you measure from its base on the ocean floor to its summit, it is taller than Mount Everest.

The summit contains the Mokuʻāweoweo caldera, which is composed of three overlapping pit craters. This caldera formed between 1,000 and 1,500 years ago. It was created when a large eruption emptied a shallow magma chamber, causing the ground to collapse.

Two prominent rift zones extend from the summit, acting as pathways for volcanic activity. The first rift zone trends southwest from the caldera toward the sea. It features a notable 40-degree change in direction along its length. The second rift zone trends northeast toward the city of Hilo. This zone is marked by a succession of cinder cones, such as the high Puu Ulaula. These rift zones are driven by dike intrusions, which are vertical sheets of magma that force their way through the crust. Scientists use radar to model the magma chamber, which sits about 3 miles below sea level.

The history of Mauna Loa includes many documented eruptions and significant human impacts. There have been 34 eruptions since the first well-documented event in 1843. Most recently, the volcano erupted from November 27 to December 13, 2022. While recent eruptions have not caused deaths, past events were destructive. Eruptions in 1926 and 1950 destroyed entire villages. Additionally, the city of Hilo is partially built upon lava flows from the late 19th century.

Mauna Loa also has complex relationships with its neighboring volcanoes, especially Kīlauea. Although they look connected, chemical analysis shows they have separate magma chambers. They do interact, however, through pressure and movement. Mauna Loa is slowly slumping eastward along its southwestern rift zone. This movement pushes against Kīlauea, driving it eastward at about 0.08 inches per year. This interaction has caused large earthquakes and created a debris area known as the Hilina Slump. Scientists have observed that high activity in one volcano sometimes coincides with low activity in the other.

Because of its power, Mauna Loa is a vital site for scientific research. The Hawaiian Volcano Observatory has monitored the mountain since 1912. The volcano is part of the Decade Volcanoes program, which focuses on the world's most dangerous volcanoes. Near the summit, the Mauna Loa Observatory studies the atmosphere. The Mauna Loa Solar Observatory studies the Sun.

These facilities allow researchers to study both Earth and space from a unique high-altitude location. The volcano remains a central part of the Hawaii Volcanoes National Park.