A small amount of geologic activity, known as intraplate activity, does not take place at plate boundaries but within a plate instead. Mantle plumes are pipes of hot rock that rise through the mantle. The release of pressure causes melting near the surface to form a hotspot. Eruptions at the hotspot create a volcano. Hotspot volcanoes are found in a line (Figure 1.1). Can you figure out why? Hint: The youngest volcano sits above the hotspot and volcanoes become older with distance from the hotspot.
intraplate activity in the oceans
The first photo above is of a volcanic eruption in Hawaii. Hawaii is not in western North America, but is in the central Pacific ocean, near the middle of the Pacific Plate. The Hawaiian Islands are a beautiful example of a hotspot chain in the Pacific Ocean. Kilauea volcano lies above the Hawaiian hotspot. Mauna Loa volcano is older than Kilauea and is still erupting, but at a slower rate. The islands get progressively older to the northwest because they are further from the hotspot. This is because the Pacific Plate is moving toward the northwest over the hotspot. Loihi, the youngest volcano, is still below the sea surface. Since many hotspots are stationary in the mantle, geologists can use some hotspot chains to tell the direction and the speed a plate is moving (Figure 1.2). The Hawaiian chain continues into the Emperor Seamounts. The bend in the chain was caused by a change in the direction of the Pacific Plate 43 million years ago. Using the age and distance of the bend, geologists can figure out the speed of the Pacific Plate over the hotspot. The Hawaiian Islands have formed from volcanic eruptions above the Hawaii hotspot.
intraplate activity on the continents
The second photo in the introduction is of a geyser at Yellowstone National Park in Wyoming. Yellowstone is in the western U.S. but is inland from the plate boundaries offshore. Hotspot magmas rarely penetrate through thick continental crust, so hotspot activity on continents is rare. One exception is the Yellowstone hotspot (Figure 1.3). Volcanic activity above the Yellowstone hotspot on can be traced from 15 million years ago to its present location on the North American Plate. The ages of volcanic activity attributed to the Yellowstone hotspot. Click image to the left or use the URL below. URL:
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loihi is actively erupting and is not an island yet, kilauea is actively erupting, mauna loa erupts some, and mauna kea erupts rarely. why the difference?
--> a) loihi and kilauea are on the hotspot, mauna loa is moving off, and mauna kea has b) this pattern is random and will change over time. c) the volcanoes that are erupting less are on the hotspot and loihi and kilauea are moving off the hotspot. d) none of the above
geologic activity that takes place away from the plate boundary.
a) divergent activity b) strike-slip activity --> c) intraplate activity d) conplate activity
a plume of hot material that results in intraplate volcanic activity is a
--> a) mantle plume b) geyser c) volcanic eruption d) pyroclastic flow
in a hotspot volcano chain, like hawaii, the age of the volcanoes
a) is all the same. --> b) is youngest on top of the hotspot and oldest furthest away. c) is oldest on top of the hotspot and youngest furthest away. d) is random along the chain.
what caused the big bend in the hawaii-emperor volcanic chain?
a) the hawaii hotspot moved. b) the pacific plate changed speed. c) the emperor hotspot shut off and the hawaii hotspot began erupting. --> d) the pacific plate changed its direction of motion.
hotspot volcanoes are only found on oceanic crust.
a) true --> b) false
all of the major geological activity takes place along plate boundaries.
a) true --> b) false
scientists use rocks from hotspot volcanoes to tell the speed a plate is traveling. for this to be accurate, what must be true?
a) the volcanoes must erupt at the same rate. b) the plate must be traveling at a constant speed. --> c) the hotspot must not move in the mantle. d) the hotspot must put out lava at a constant speed.
the only intraplate activity known is volcanic activity.
a) true --> b) false
hotspot volcanoes are as common on continental crust as on oceanic crust.
--> a) true b) false
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