4.7 Hotspots: Origin and Examples

• Hotspots are volcanic regions thought to be fed by anomalously hot mantle compared to its surroundings.
• They can exist on, near, or far from tectonic plate boundaries.

Origin Explanations

• One attributes hotspots to hot mantle plumes rising as thermal diapirs from the core-mantle boundary.
• The other suggests lithospheric extension allows passive melt rise from shallow depths, questioning if hotspots are actually anomalously hot.
• Hawaii and Yellowstone are examples of hotspots.

Background Information

• J. Tuzo Wilson (1963) first linked the Hawaiian Islands to a tectonic plate's slow movement over a hot region.
• Hotspots are believed to be fed by narrow streams of hot mantle, called mantle plumes, rising from the Earth's core-mantle boundary.
• The existence of mantle plumes is debated in Earth science.
• Estimates for the number of hotspots fed by mantle plumes range from 20 to thousands.
• Most geologists believe only a few tens exist.
• Hawaii, Réunion, Yellowstone, Galápagos, and Iceland are active volcanic regions under the hypothesis.
• Most hotspot volcanoes are basaltic, making them less explosive than subduction zone volcanoes where water is trapped.
• In continental regions, basaltic magma rises through the crust and melts to form rhyolites may cause violent eruptions.
• The Yellowstone Caldera formed this way.
• After rhyolite eruption, basaltic magma may rise through the same fissures, like the Ilgachuz Range in British Columbia with its trachyte, rhyolite, and basaltic lava flows.
• The hotspot hypothesis is linked to the mantle plume hypothesis.

Hotspot Volcanoes vs Island Arc Volcanoes

• Hotspot volcanoes differ in origin from island arc volcanoes.
• Island arcs form over subduction zones at converging plate boundaries.
• One oceanic plate descends into a trench when meeting another.
• The subducting plate releases water into the overriding plate, altering its composition and causing rock to melt and rise, fueling volcanoes like the Aleutian Islands near Alaska.

Hotspot Volcanic Chains

• The mantle plume/hotspot hypothesis suggests fixed feeder structures and drifting continents/seafloor.
• This predicts time-progressive volcano chains on the surface.
• Yellowstone, has progressively older extinct calderas to the west.
• The Hawaiian archipelago has progressively older, more eroded islands to the northwest.
• Geologists use hotspot volcanic chains to track tectonic plate movement, an effort challenged by short, non-progressive chains and hotspots that may not be fixed.

Postulated Hotspot Volcano Chains

• Kilauea is the world's most active shield volcano, erupting since 1983, and part of the Hawaiian-Emperor seamount chain.

Examples of Chains

• Hawaiian-Emperor seamount chain (Hawaii hotspot)
• Louisville seamount chain (Louisville hotspot)
• Walvis Ridge (Gough and Tristan hotspot)
• Kodiak–Bowie Seamount chain (Bowie hotspot)
• Cobb-Eickelberg Seamount chain (Cobb hotspot)
• New England Seamount chain (New England hotspot)
• Anahim Volcanic Belt (Anahim hotspot)
• Mackenzie dike swarm (Mackenzie hotspot)
• Great Meteor hotspot track (New England hotspot)
• St. Helena Seamount Chain – Cameroon Volcanic Line (Saint Helena hotspot)
• Southern Mascarene Plateau–Chagos-Maldives-Laccadive Ridge (Réunion hotspot)
• Ninety East Ridge (Kerguelen hotspot)
• Tuamotu–Line Island chain (Easter hotspot)
• Austral–Gilbert–Marshall chain (Macdonald hotspot)
• Juan Fernández Ridge (Juan Fernández hotspot)

Intraplate Activity

• Intraplate activity describes geologic activity within a plate, not at plate boundaries.
• Mantle plumes are pipes of hot rock rising through the mantle.
• Pressure release causes melting near the surface, forming a hotspot where eruptions create a volcano.
• Hotspot volcanoes form a line because the youngest volcano sits above the hotspot, and volcanoes get older with distance.
• Kilauea volcano lies above the Hawaiian hotspot.
• Mauna Loa volcano is older than Kilauea, but still erupting at a lower rate.
• Islands get progressively older northwest of the hotspot.
• Loihi, the youngest volcano, is still below the sea surface.
• The Hawaiian chain continues into the Emperor Seamounts and its bend indicates a change in the direction of the Pacific plate 43 million years ago.
• The age and distance of the bend reveal the speed of the Pacific plate over the hotspot.
• Hotspot magmas rarely penetrate thick continental crust, but Yellowstone is an exception.
• Volcanic activity above the Yellowstone hotspot can be traced back 15 million years.