Comment: 03:46 - 05:20 (01:34)
Source: Annenberg/CPB Resources - Earth Revealed - 13. Volcanism
Keywords: "Robert Tilling", volcano, plate, magma, "pillow lava", fissure, temperature, Hawaii, "divergent plate", "Pacific Plate", basalt, "lava flow", eruption, "oceanic hot spot"
Our transcription: Most undersea volcanoes lie along divergent plate boundaries.
Here, runny basaltic lava as hot as 1200 degrees centigrade pours quietly through fissures, much of it cooling in the dark water to form flows of bulbous rock called "pillow" lava.
Other oceanic volcanoes, such as those of the Hawaiian chain, do not lie on divergent plate boundaries.
The Hawaiian volcanic chain occurs in the middle of the Pacific Plate, far removed from any plate boundary.
In the best hypothesis that has been evoked so far to explain that is called a "Hawaiian Hot Spot Hypothesis".
What that entails is a hot spot, a zone of melting deep in the mantle over which the Pacific Plate rides to the northwest as part of the plate motions, and that this heat source, then, or hot spot actually locally melts the overriding solid rock to form the basaltic magmas which then erupt.
Then, as the plate continues to move, the volcano that had formed and is transported to the northwest, it ultimately gets severed from the feeding magma source and becomes extinct.
However, then over the same place, a new volcano starts to form as more magma is melted and a new island forms.
So that the chain of Hawaiian Islands actually show an age progression going from the southeast, which is now currently over the hot spot, going to the northwest.
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