The 13 large islands, six small islands and 42 islets of the Galapagos are the product of a hotspot.
Hotspots are thermal plumes of hot magma underneath tectonic plates. As they melt through the overlying crust, they produce different types of volcanic activity that, in turn, produces different kinds of landforms. Hotspots under oceanic plates form island arcs, while hotspots under continental plates form large calderas.
Hotspot Basics
In 1963, Tuzo Wilson, who also discovered transform faults, realized a need within geology to account for isolated areas of long-term volcanic activity not associated with plate boundaries. He reasoned that these locations required small, long-lasting and very hot sources of magma under them. He devised a hotspot theory which proposed that these hotspots were fueled by thermal plumes that rose from deep in the mantle and were stationary, allowing the tectonic plates to move over them.
Number and Location of Hotspots
Hotspots can be found around the globe, occurring under oceanic and continental plates. Of the more than 100 hotspots that have been active during the past 10 million years, most have occurred under plate interiors. However, they can also be found at divergent boundaries, such as beneath Iceland, the Azores and the Galapagos Islands. According to the United States Geological Survey, of the 25 prominent hotspots as of 1999, only five were under continental plates. These included Yellowstone and five in Africa.
Oceanic Hotspot Landforms
Oceanic hotspots typically produce fluid basaltic lava flows, leading to the creation of shield volcanoes. Furthermore, as the plate slowly moves over the hotspot, the result is an island arc composed of a long ridge dotted by shield volcanoes. The Hawaiian Islands are a perfect example of this process. The Hawaiian Ridge traces the movement of the plate over the hotspot. Along this ridge, the Hawaiian Islands rise to break the surface in a chain. The oldest rocks on Kauai, the most northwestern island, are approximately 5.5 million years old, while the oldest rocks on Hawaii, the most southeastern island, are only 700,000 years old. Other examples of hotspot island chains include the Marquesas, Society, Pitcairn, Samoan, Galapagos and Azores archipelagos. Of these, the Galapagos and Azores are located near plate boundaries.
Continental Hotspot Landforms
Continental hotspots are rarer and produce an entirely different type of lava, produced from rhyolite magma. This magma is thick, gas-rich and highly explosive. As a result, the landforms produced by continental hotspots are quite different from oceanic ones. These hotspots produce supervolcanoes that, once they erupt, collapse into enormous calderas. The Yellowstone hotspot that lies under the North American plate is a prime example. Three volcanic eruptions have occurred during the last two million years; the most recent was 600,000 years ago. These eruptions produced three massive calderas that form a chain, much like the Hawaiian Islands, that traces the movement of the plate over the hotspot. The size of the most recent caldera is 28 miles by 47 miles. The Toba supervolcano, located in Indonesia, left a caldera that is 62 miles by 22 miles. This caldera is now a large lake.
Tags: continental plates, Hawaiian Islands, million years, over hotspot, Galapagos Azores, have occurred
