Mauna Loa Eruption 2022: Earthquake Patterns and Magma Dynamics

Mauna Loa, the world’s largest active volcano, erupted in late November 2022 for the first time since 1984. The eruption sent lava flows down its slopes and released volcanic gases into the atmosphere, drawing global attention to Hawaii’s seismic and volcanic activity. While no major damage occurred, the event provided valuable data on the volcano’s behavior before and during an eruption.

Understanding the earthquake patterns and magma dynamics that preceded the eruption helps scientists refine monitoring techniques and improve hazard predictions.

Geologic Context

Mauna Loa’s immense size and activity stem from its position over the Hawaiian hotspot, a fixed plume of molten rock rising from the mantle. Unlike plate boundary volcanoes, which form due to subduction or rifting, Mauna Loa is a shield volcano built by successive eruptions of low-viscosity basaltic lava. This process has allowed it to grow to an elevation of 4,169 meters (13,681 feet) above sea level, with its base extending below the ocean surface, making it the tallest mountain on Earth when measured from its submerged foundation.

The Hawaiian hotspot has been active for tens of millions of years, generating a chain of volcanic islands as the Pacific Plate moves northwestward. Mauna Loa, the largest of these volcanoes, has been erupting for at least 700,000 years, with subaerial lavas dating back approximately 200,000 years. Its long history of eruptions has shaped the Big Island’s landscape, forming extensive lava fields and influencing local ecosystems. The volcano’s activity is driven by a continuous supply of magma from the hotspot, which accumulates in a system of reservoirs beneath the surface.

Mauna Loa’s structure includes two primary rift zones—the Northeast Rift Zone and the Southwest Rift Zone—along with the summit caldera, Mokuʻāweoweo. These rift zones serve as pathways for magma movement, with eruptions often occurring along fissures. The summit caldera, formed by past collapses, acts as a focal point for magma accumulation before it migrates into the rift zones. The interplay between these geological features influences eruption style, with some events confined to the summit while others produce extensive lava flows. The 2022 eruption originated in Mokuʻāweoweo before migrating to the Northeast Rift Zone, a pattern observed in previous eruptions.

Pre-Eruption Earthquake Patterns

Seismic activity in the months before Mauna Loa’s 2022 eruption signaled the volcano’s reawakening. Earthquake swarms, clusters of small to moderate tremors, became more frequent beneath the summit and along the rift zones, indicating increased magma movement. The depth, magnitude, and location of these earthquakes allowed volcanologists to track pressurization in the magma system. A shift from deep, long-period tremors to shallower, high-frequency earthquakes signaled magma rising toward the surface.

The earthquake distribution followed a pattern consistent with past eruptions. Initial seismic activity was concentrated beneath Mokuʻāweoweo at depths of 3 to 5 kilometers (1.9 to 3.1 miles), suggesting increasing pressure in the magma reservoir. As the eruption approached, earthquake epicenters migrated toward the upper Northeast Rift Zone, reflecting magma intrusion. This shift was accompanied by an increase in both frequency and magnitude, with some tremors exceeding magnitude 3.0, indicating magma forcing its way into fractures.

Tiltmeter and GPS data confirmed the seismic evidence, showing measurable summit inflation as magma accumulated beneath the caldera. In the hours before the eruption on November 27, 2022, seismicity surged, with hundreds of earthquakes recorded in rapid succession. These final tremors were concentrated along the Northeast Rift Zone, confirming the eruption would emerge from fissures in this area.

Magma Chamber Dynamics

Beneath Mauna Loa, a network of magma reservoirs regulates eruption timing and intensity. The primary chamber, several kilometers beneath the summit caldera, serves as a staging ground where molten rock accumulates under pressure. Over time, this reservoir undergoes cycles of inflation and deflation as magma rises from the mantle and either remains stored or migrates into the rift zones. The 2022 eruption followed years of gradual inflation, detected through satellite-based interferometric synthetic aperture radar (InSAR) and GPS measurements, which revealed surface deformation indicative of magma influx.

As pressure increased, stress transferred to surrounding rock, promoting the formation and reactivation of fractures. This created pathways for magma ascent, evident in shifting earthquake patterns. The transition from deep-seated storage to shallower reservoirs determined where lava would emerge. While some intrusions remain trapped, the 2022 event saw magma breach the surface after migrating from the summit chamber into the Northeast Rift Zone, following structural weaknesses that had guided previous eruptions.

Temperature and composition within the magma chamber also influenced eruption dynamics. High-temperature basaltic magma, rich in dissolved gases, exerted additional pressure as volatile elements expanded during ascent. This pressurization accelerated magma movement, contributing to the rapid onset of surface activity once fissures opened. The presence of hotter, less evolved magma in 2022 suggested a direct supply from deeper reservoirs, leading to highly fluid lava flows that advanced swiftly downslope.

Lava Composition and Flow Characteristics

The lava emitted during the 2022 eruption was predominantly tholeiitic basalt, a low-viscosity magma rich in iron and magnesium but relatively poor in silica. This composition allowed lava to flow rapidly before cooling and solidifying. Unlike stratovolcanoes, where higher silica content leads to explosive eruptions, Mauna Loa’s basaltic lava remains fluid, producing effusive eruptions characterized by steadily advancing flows rather than violent explosions. The high-temperature magma, exceeding 1,100°C (2,012°F), maintained mobility for extended periods, influencing flow speed and reach.

Once fissures opened along the Northeast Rift Zone, lava fountains reached heights of up to 50 meters (164 feet), feeding fast-moving channels toward lower elevations. Flow speed varied with terrain slope and lava discharge rate, with steeper gradients facilitating rapid movement. In some areas, pāhoehoe lava—a smooth, ropy form—dominated, while in others, ‘a‘ā lava, with a jagged, clinker-like surface, took over as the flow cooled and became more viscous. The transition between these textures was influenced by eruption rate, cooling time, and ground morphology.

Volcanic Gas Signatures

The 2022 eruption released a complex mixture of volcanic gases, with sulfur dioxide (SO₂) being the most abundant. This gas reacts with water vapor to form sulfate aerosols, affecting air quality and climate conditions. During the eruption’s peak, SO₂ emissions exceeded 200,000 metric tons per day, comparable to previous Mauna Loa eruptions. These emissions contributed to volcanic smog, or “vog,” which posed respiratory risks to local communities. Wind patterns dictated vog dispersion, with trade winds carrying the gas plume westward over the Pacific Ocean, reducing its concentration over inhabited areas.

In addition to SO₂, the eruption released carbon dioxide (CO₂) and water vapor, both originating from deep within the Earth’s mantle. While Mauna Loa’s CO₂ emissions are lower than those from more explosive volcanoes, they provide insight into magma degassing. The CO₂ to SO₂ ratio in the gas plume helped volcanologists assess magma depth, as higher CO₂ concentrations often indicate deeper magma. Hydrogen sulfide (H₂S) was detected in trace amounts but remained well below harmful levels. The composition of these gases influenced air quality and served as a tool for understanding magma dynamics, as shifts in gas ratios often precede changes in eruption behavior.