Hot Spot VolcanismAll of the mountains in this map of the floor of the Pacific Ocean are volcanoesNote that there are several long chains of volcanoesBut there are also many individual volcanoesNone of these volcanoes are formed along plate boundaries

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Hot Spot Volcanism

These isolated areas of volcanic activity are not associated with plate boundariesThese volcanoes are found both on continents and out in the ocean

Hot Spot Volcanism

A plume of hot mantle material rises up to the bottom of the lithosphere Melting occurs and magma is createdThese are called “hot spots”They can last for many millions of years

Hot Spot VolcanismThe magma works its way to the surface over the hot spot and a volcano is formedOut in the ocean, the volcano may or may not reach the surface and form an islandIn fact, few oceanic volcanoes reach the surface

Hot Spot VolcanismAs the moving plate carries the volcano away from the hot spot, the volcano dies outWith time, another volcano may form This cycle may repeat many times, forming a long chain of under sea volcanoes and islands

Hot Spot VolcanismThe Cortes Bank Seamount, 100 miles offshore of San Diego, is a 17-mile long remnant of a undersea volcanic mountain range that rises to within 3 feet of the surface

Hot Spot VolcanismFisherman and scuba divers knew about it, but it was not on any nautical mapsThe U.S. Navy found it the hard way in 1985 with the aircraft carrier Enterprise

Hot Spot Volcanism“To get the biggest waves at Cortes Bank, you need light winds, low tides, and big storm swells from the northwest all at the same time, a Pacific surfer's version of the ‘perfect storm’.”

The Hawaiian Islands are the classic example of hot spot volcanism

Hot Spot Volcanism

Hot Spot VolcanismEvery island in the Hawaiian Island chain was created by volcanic eruptions that occurred as the Pacific Oceanic Plate crossed over a hot spot

Hot Spot VolcanismIn fact, the 7 main Hawaiian Islands are just the southern most portion of two great undersea mountain ranges, composed of hundreds of volcanoes, that runs for 6000 kilometers (4000 miles) across the floor of the Pacific Ocean

Hot Spot Volcanism

The plate has moved to the northwest for more than 65 million yearsThe big island of Hawaii is now over the hot spot

The volcanoes that formed the Hawaiian islands are classified as shield volcanoes

Hot Spot Volcanism

Hot Spot VolcanismShield volcanoes are characterized by broad, gentle slopes built up from repeated basaltic lava flows

Hot Spot VolcanismNot all eruption create big islandsMolokini represents one eruption that is slowly being reclaimed by the sea

Hot Spot VolcanismLoihi Volcano, the youngest volcano of the Hawaiian Island Chain, lies about 20 km off the south coast of the Big IslandCurrently it rises 3500 meters above the surrounding sea floor and its summit is about 1000 meters beneath the surface