Kilauea, located on Hawaii’s Big Island, is one of the world’s most active volcanoes, known for its dynamic eruptions. This shield volcano has been in a state of nearly constant activity. Its frequent eruptions result from complex geological processes, involving magma movement through its internal structure. Understanding Kilauea’s consistent activity involves examining its origin, magma pathways, and immediate eruption catalysts.
Kilauea’s Hotspot Origin
Kilauea’s persistent activity stems from the Hawaiian hotspot, a phenomenon distinct from volcanoes at tectonic plate boundaries. This hotspot is a stationary plume of superheated rock rising from deep within the Earth’s mantle. As the Pacific Plate moves over this fixed mantle plume, intense heat causes partial melting of the rock beneath.
This continuous melting and plate movement forms a chain of volcanoes across the ocean floor, known as the Hawaiian-Emperor seamount chain. Each island becomes progressively older and less active as it moves northwest from the hotspot. Kilauea, directly over the hotspot, is the youngest and most active volcano on the Big Island. The buoyant magma rises through weak zones in the Earth’s crust, erupting to build the massive shield volcanoes that form the Hawaiian Islands.
The Volcano’s Internal Plumbing
Kilauea’s eruptive behavior is linked to its complex internal plumbing system, which stores and moves magma. Beneath its summit caldera, Halemaʻumaʻu, lies a shallow magma reservoir, typically 0.5 to 2 kilometers (0.3 to 1.2 miles) below the surface. A deeper, larger reservoir, 3 to 5 kilometers (2 to 3 miles) beneath the southern caldera, feeds the shallower system.
Magma from these reservoirs can erupt at the summit or migrate laterally into Kilauea’s extensive rift zones. The volcano features two primary rift zones: the East Rift Zone (ERZ) and the Southwest Rift Zone (SWRZ). The East Rift Zone is significantly longer, while the Southwest Rift Zone is shorter and historically less active.
These rift zones are areas of structural weakness, providing pathways for magma to travel underground from the summit storage regions. When magma moves from the summit reservoir into a rift zone, it causes a noticeable deflation of the summit region. This lateral intrusion of magma into the rift zones is a common precursor to flank eruptions, as the magma exploits these weaknesses to reach the surface.
Immediate Triggers of Eruptions
While the hotspot provides the continuous supply of magma, specific conditions and events act as immediate catalysts for Kilauea’s eruptions. A primary indicator of impending activity is a change in pressure within the volcano’s magma plumbing system, often observed through ground deformation. Instruments like tiltmeters detect subtle tilting of the ground, with inflation indicating magma rising into the summit reservoir and deflation suggesting magma is moving away, either towards a rift zone or an eruption.
Increased seismicity, in the form of elevated earthquake activity, also signals magma movement. These earthquakes often concentrate at depths of 2 to 4 kilometers (approximately 1.2 to 2.5 miles) beneath the surface during magma intrusions into the rift zones. Such seismic swarms, combined with ground deformation patterns, provide scientists with crucial real-time data about the volcano’s internal state.
Magma can also force its way through existing cracks, forming planar intrusions known as dikes. These dike intrusions are common precursors to eruptions, as the magma pushes through the rock, causing ground deformation and increased seismicity. Furthermore, significant events like summit collapses can directly influence or trigger eruptions in the rift zones by altering pressure dynamics within the system. For instance, the 2018 eruption saw magma drain from the summit reservoir, leading to a dramatic summit collapse, as the magma moved into and erupted from the Lower East Rift Zone.