Hotspot

A hotspot is a “poker” of intense heat rising from deep within the Earth’s mantle, capable of melting the crust above it to form volcanoes. Unlike the majority of the world’s volcanoes, which form at the edges of tectonic plates, hotspots often punch through the middle of plates, thousands of kilometers from the nearest boundary. The theory was first proposed by geophysicist J. Tuzo Wilson in 1963 to explain the puzzling existence of the Hawaiian Islands—a chain of progressively older volcanic islands in the middle of the Pacific Ocean.

The Mechanism: A Geological Blowtorch

Hotspots are powered by mantle plumes—long, narrow columns of superheated rock that rise from the boundary between the mantle and the Earth’s core (the core-mantle boundary, at ~2,900 km depth).

• Stationary Heat: While tectonic plates are constantly drifting across the planet’s surface at speeds of a few centimeters per year, mantle plumes are thought to remain relatively stationary over long periods of time.
• Burning Through: As the plume head hits the underside of the lithosphere (crust + upper mantle), the immense heat causes decompression melting. As the mantle rock rises, the decreasing pressure allows it to melt even without a significant temperature increase, generating basaltic magma.
• Eruption: This magma rises through the lithosphere and eventually erupts at the surface, building a volcano directly over the plume.

The heat flux at a hotspot can be dramatically higher than the surrounding mantle. Hawaii sits on mantle that is approximately 150–200°C hotter than normal, generating the enormous volumes of lava that have built the Hawaiian island chain over tens of millions of years.

The Conveyor Belt Effect

Because the plate moves while the hotspot stays put, the result is a linear chain of volcanoes that get progressively older in the direction of plate movement.

1. Active Stage: A volcano forms directly over the hotspot (e.g., the Big Island of Hawaii, specifically the Kīlauea and Mauna Loa volcanoes).
2. Drift: The movement of the tectonic plate carries the volcano away from the heat source, cutting off its magma supply.
3. Extinction: Cut off from its magma supply, the volcano goes extinct, cools, and begins to erode. The island shrinks due to wave erosion and subsidence (thermal cooling of the seafloor).
4. New Birth: A new island or seamount begins to grow over the hotspot behind the old one.

Analogy: Imagine slowly moving a sheet of paper over a stationary candle flame. You will end up with a line of scorch marks. The paper is the tectonic plate; the candle is the hotspot.

The Hawaiian-Emperor Seamount Chain is the textbook example. It stretches 6,000 km across the Pacific, from the active Big Island to the 85-million-year-old Meiji Seamount near the Kamchatka Trench. A pronounced kink in the chain, the Hawaiian-Emperor Bend, formed ~47 million years ago and records a dramatic change in the direction of Pacific Plate motion.

Types of Hotspots

Oceanic Hotspots (Hawaii)

When a hotspot sits under thin oceanic crust (~7 km thick), it typically produces large volumes of basaltic lava, building massive shield volcanoes. Oceanic hotspots are relatively “clean”—the basaltic lava produced is minimally contaminated by assimilating the thin crust.

• The current active hotspot beneath Hawaii is fueling the eruptions of Kīlauea and Mauna Loa, and is already building the next island: Lōʻihi Seamount is a submarine volcano growing on the ocean floor southeast of the Big Island, currently ~1 km below sea level. It is expected to emerge above the ocean surface in roughly 10,000–100,000 years.

Continental Hotspots (Yellowstone)

When a hotspot sits under thick continental crust (~35–70 km thick), the dynamics change dramatically. The rising basaltic magma has difficulty penetrating the thick, buoyant crust. Instead, its heat partially melts the base of the continental crust, generating large volumes of silica-rich rhyolitic magma—far more viscous and gas-charged than basalt. This leads to catastrophic explosive eruptions rather than gentle lava flows.

• Track: The path of the Yellowstone hotspot can be traced backwards across the Snake River Plain in Idaho, a topographic and volcanic scar left as the North American Plate moved southwest over the plume over the past 17 million years. The hotspot’s track records a history of massive caldera-forming eruptions, the most recent of which (the Lava Creek eruption, ~640,000 years ago) produced the current Yellowstone Caldera.
• The Columbia River Flood Basalts (~17–14 million years ago) in Oregon and Washington are thought to represent the initial head of the Yellowstone plume impacting the lithosphere—one of the largest outpourings of lava in Earth’s geologic record.

Evidence for the Plume Origin

The existence of deep mantle plumes as the source of hotspots has been debated, but several lines of evidence support the model:

• Seismic tomography: Imaging of the mantle using earthquake waves reveals anomalously hot (slow-velocity) columns extending downward from major hotspots. Beneath Hawaii, a slow anomaly extends to depths of at least 1,000 km.
• Helium isotope ratios: Plume-related lavas often have distinctively high ³He/⁴He ratios, reflecting primitive, undegassed mantle material that has been isolated deep in the mantle since Earth’s formation—distinct from the recycled material typical of subduction-zone and mid-ocean-ridge lavas.
• Age progressions: The systematic increase in age along island chains like Hawaii or the Tristan da Cunha chain in the South Atlantic matches the predicted geometry of a fixed plume beneath a moving plate.

Global Inventory of Hotspots

Approximately 40–50 hotspots are currently recognized worldwide, though the exact number is debated. Well-documented examples include:

• Hawaii (Pacific): The paradigm case; responsible for the world’s most active volcanoes.
• Yellowstone (USA): A continental hotspot responsible for multiple supervolcanic eruptions.
• Iceland: Situated directly on the Mid-Atlantic Ridge, creating an unusually thick and topographically elevated section of the ridge; responsible for Iceland being the only part of the Mid-Atlantic Ridge that rises above sea level.
• Réunion (Indian Ocean): Currently the site of the highly active Piton de la Fournaise; the same hotspot is believed to have generated the Deccan Traps flood basalts 66 million years ago.
• Galápagos (Pacific): Responsible for the volcanic islands made famous by Darwin’s observations on evolution.

Related Terms

Mantle plume is the deep-seated upwelling of hot mantle rock that drives a hotspot. Shield volcano is the characteristic type of volcano built above an oceanic hotspot. Flood basalt describes the enormous outpourings associated with the initial arrival of a plume head. Seamount is a submerged, extinct volcanic peak in a hotspot chain.