Earth Science: Geology, the Environment, and the Universe

Chapter 20: Mountain Building

Problem of the Week

Up From the Deep

In this chapter on mountain building, and in previous chapters, you have learned that mountains form in a variety of ways. Much of the time mountain formation is associated with the collision of plates. At other times they are the result of massive uplifting of the crust, or from large scale faulting. Sometimes mountains form as volcanoes, which are not associated with plate boundaries but with hot spots. Hot spots are believed to be places where magma from the mantle rises to the surface at a relatively permanent location, usually not at a plate boundary.

When you look at a map of the Hawaiian Islands, you can see that they form a chain.

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This chain of islands is believed to have formed as the Pacific Plate has moved slowly over the top of a hot spot. As would be expected, the island currently located over the hot spot (Hawaii) contains active volcanoes, such as Kilauea and Mauna Loa. As the plate continues to move, the big island of Hawaii and its active volcanoes will eventually move off the hot spot, and the volcanoes will become inactive. As would be predicted, scientists have discovered that there is a new volcano, called Loihi (or Lo’ihi), forming beneath the ocean about 30 km to the southeast of the youngest volcano on the island of Hawaii—Kilauea.

Relatively active since 1996, Loihi’s peak rises to within 969 m of sea level. The seafloor lies more than 3 kilometers below the peak. Volcanoes on the ocean floor, such as Loihi, usually erupt nonexplosively with gentle outpourings of lava. After about 200,000 years of recurring eruption and layer upon layer of lava, a submarine shield has formed at Loihi. Loihi has a summit caldera and active vents around the summit.

Following this nonexplosive stage, more violent eruptions may begin as the mountain grows upward and reaches within a few hundred feet of the ocean surface. The confining pressure is low at shallow depths, and explosions of ash-laden steam become more common. Loihi is probably 100,000 years away from this more explosive stage of volcanism.

Problem:

Given the information above, and the estimated rate of plate movement (7.62 cm per year to the west-northwest relative to the Hawaiian hot spot) calculate the location of Loihi at the point in time when your estimate puts its peak at sea level. Will its peak break the surface before the plate movement carries it beyond the source of magma—the hot spot?

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