Kīlauea, one of the world’s most active volcanoes, is a dominant feature on the southeastern shore of the Island of Hawaiʻi. This shield volcano has been in a state of near-constant activity, making it a prime location for studying volcanic processes. Understanding Kīlauea’s eruptions requires examining the long-term geological conditions, the internal pathways that transport magma, and the immediate pressure changes that force magma to the surface.
The Hotspot Origin
Kīlauea’s existence is fundamentally tied to the Hawaiian Hotspot, a phenomenon where a stationary column of superheated rock, known as a mantle plume, rises from deep within the Earth. This plume originates near the boundary between the Earth’s core and mantle. The intense heat causes the rock in the upper mantle to partially melt, generating magma.
The Pacific Plate, a massive segment of the Earth’s crust, is slowly moving northwestward over this relatively fixed hotspot. As the plate moves, the continuous supply of magma punches through the crust, building a succession of volcanoes that form the Hawaiian-Emperor seamount chain. Kīlauea is currently positioned directly above the plume’s activity, making it one of the youngest and most active volcanoes in the chain.
Magma Movement and Eruption Pathways
Once magma is generated deep within the mantle, it rises and collects in a complex plumbing system beneath the volcano’s surface. At the summit, a shallow magma reservoir exists roughly one to two kilometers below the caldera floor, specifically beneath the Halemaʻumaʻu crater. This central reservoir acts as the primary storage and distribution center for the volcano. The pressure within this reservoir fluctuates constantly as new magma arrives from depth or is pushed sideways.
Extending outward from the summit are two structural weak points in the volcano’s flank: the East Rift Zone and the Southwest Rift Zone. These rift zones are long, linear fractures that act as underground conduits, allowing magma to travel laterally away from the summit. The East Rift Zone, which extends for about 125 kilometers, is particularly active, often leading to eruptions miles away from the main caldera. This rift system is hydraulically connected to the summit reservoir, meaning pressure changes in one area quickly affect the other.
Immediate Triggers of Eruption
Eruptions result from an increase in magmatic pressure that exceeds the strength of the surrounding rock, forcing a pathway to the surface. This pressure increase can stem from a surge in the magma supply rate from the deep mantle or a blockage that prevents the stored magma from flowing freely. Monitoring instruments, such as tiltmeters and GPS stations, detect this build-up as ground inflation and uplift around the summit. When the pressure becomes too great, the magma forces its way into vertical cracks, a process known as a dike intrusion.
A dike intrusion involves a blade-like sheet of magma moving through the rock, often accompanied by earthquakes that track its underground path. During the 2018 event, a massive dike intrusion propagated down the East Rift Zone, causing a significant drainage of the summit magma chamber. This drainage caused the summit caldera to collapse and led to a prolonged flank eruption in the lower rift zone. These events highlight how the interplay between high magma supply and structural adjustments, such as ground deformation or seismic activity, provides the immediate trigger for Kīlauea’s frequent eruptions.