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.

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.

• Stationary Heat: While tectonic plates are constantly drifting across the planet’s surface, mantle plumes are thought to remain relatively stationary.
• Burning Through: As the plume head hits the underside of the lithosphere (crust), the immense heat acts like a blowtorch, melting the rock and creating a volcanic vent on the surface.

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.

1. Active Stage: A volcano forms directly over the hotspot (e.g., Kīlauea).
2. Drift: The movement of the tectonic plate carries the volcano away from the heat source.
3. Extinction: Cut off from its magma supply, the volcano goes extinct, cools, and begins to erode.
4. New Birth: A new island 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.

Types of Hotspots

1. Oceanic Hotspots (Hawaii)

When a hotspot sits under thin oceanic crust, it typically produces basaltic lava, building massive shield volcanoes. The Hawaiian-Emperor Seamount Chain helps track the movement of the Pacific Plate over the last 80 million years.

• Current Activity: The hotspot is currently fueling the Big Island of Hawaii and the growing submarine volcano Lōʻihi.

2. Continental Hotspots (Yellowstone)

When a hotspot sits under thick continental crust, the process is more explosive. The rising magma melts the silica-rich continental rock, creating thick, viscous, rhyolitic magma. This leads to catastrophic super-eruptions.

• Track: The path of the Yellowstone hotspot can be traced across the Snake River Plain in Idaho, showing a history of massive calderas leading up to the current location in Wyoming.

FAQ

Q: Do hotspots move? A: For a long time, they were thought to be perfectly fixed. However, recent research suggests that mantle plumes can drift slightly over millions of years due to currents in the mantle (“mantle wind”).

Q: Can a new hotspot appear? A: Yes, but it happens on geological timescales. A new plume head reaching the surface would likely cause a massive flood basalt event, covering huge areas in lava.