The Hawaiian Islands are the surface expression of a deep-seated mantle plume known as the Hawaiian hotspot, which remains relatively fixed as the Pacific tectonic plate slowly moves over it. This geological process creates a chain of volcanoes that follow a distinct evolutionary pattern of growth, dormancy, and eventual extinction.
Hawaiian volcanoes are classified as shield volcanoes, characterized by their broad, gently sloping profile. This shape results from the eruption of highly fluid, low-viscosity basaltic lava that flows easily and spreads widely. Unlike the explosive composite volcanoes found at tectonic plate boundaries, Hawaiian shield volcanoes typically feature non-explosive, effusive eruptions.
Identifying Hawaii’s Active Volcanoes
Volcanoes are categorized by their activity level: active, dormant, or extinct. An active volcano is currently erupting or showing signs of an impending eruption. A dormant volcano has not erupted recently but could potentially erupt again, while extinct volcanoes have not erupted in tens of thousands of years and are not expected to become active.
On the Island of Hawaiʻi, the two volcanoes most relevant to eruption frequency are Kīlauea and Mauna Loa, both considered active. Hualālai is also active, having last erupted in 1801, but its long-term frequency is significantly lower than its neighbors. Mauna Kea is classified as dormant, having last erupted about 4,500 years ago, and Kohala is considered extinct.
Eruption Frequency of Kilauea
Kīlauea is recognized as one of the most active volcanoes globally and is the youngest on-land volcano created by the Hawaiian hotspot. Its historical activity is marked by prolonged, continuous eruptions measured in years or decades, rather than isolated events. The most notable example is the East Rift Zone eruption, which began in 1983 and continued almost uninterruptedly for 35 years until 2018.
This persistent activity means approximately 90% of the volcano’s surface is covered by lava flows less than 1,000 years old. Eruptions primarily occur at the summit caldera, specifically the Halemaʻumaʻu crater, or along the East and Southwest Rift Zones. The 2018 lower East Rift Zone event demonstrated a shift in style, where magma migrated farther down the rift, opening two dozen fissures. More recently, activity has frequently returned to the summit, characterized by episodic lava fountaining and the formation of lava lakes. Kīlauea’s frequent, sustained activity results in an overall eruption rate much higher than any other Hawaiian volcano.
Eruption Frequency of Mauna Loa
Mauna Loa, the world’s largest active volcano, follows a less frequent but significant eruption pattern compared to Kīlauea. Since the first confirmed historical eruption in 1843, Mauna Loa has erupted 34 times. Historically, the average interval between eruptions was approximately 3.5 years before 1950.
The frequency became less predictable in the latter half of the 20th century, with only three eruptions occurring between 1950 and 2022. The 38-year period between the 1984 eruption and the 2022 event marked the longest quiet period in its recorded history. Over the longer term, geological mapping suggests Mauna Loa has produced lava flows, on average, once every six years over the past 3,000 years.
Eruptions typically begin at the summit caldera, Mokuʻāweoweo, and may migrate to one of its two major rift zones, the Northeast or Southwest. Mauna Loa’s flows are known for their high volume and potential to travel long distances quickly, increasing the hazard potential for communities on its flanks.
Monitoring and Forecasting Volcanic Activity
The U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) addresses the question of when the next eruption will occur through a comprehensive monitoring network. This network tracks changes in the volcano’s physical state, which often precede an eruption. Key indicators include ground deformation, seismic activity, and gas emissions. While this continuous monitoring allows scientists to identify shifts and trends that deviate from normal levels, the precise timing and duration of a future eruption remain challenging to forecast.
Ground Deformation
Ground movement is tracked using GPS receivers and tiltmeters, which measure changes in the volcano’s slope. Inflation, or swelling of the volcanic edifice, suggests that magma is accumulating beneath the surface. Deflation indicates magma is moving elsewhere or erupting.
Seismic Activity
Seismic monitoring uses seismometers to record the number and location of earthquakes. Increasing or shifting earthquake swarms often signal magma migrating through the crust.
Gas Emissions
Volcanic gas emissions, particularly sulfur dioxide (SO2), are measured using instruments like UV spectrometers to detect changes in the magma supply rate. A sudden, sustained increase in SO2 flux can signal that magma is rising closer to the surface.