sea90E - an oceanographic expedition to the Indian Ocean



	Hotspots and Ninetyeast Ridge: What’s a hotspot? by Dr. Will Sager, the head of our science team. Updated June 21, 2007 from The NinetyEast Ridge in the Indian Ocean What’s a hotspot? Many geoscientists think that hot rock from deep within the Earth’s mantle layer rises toward the surface like smoke on a still day. Although the mantle layer is solid rock, the intense heat inside the Earth causes this rock to flow, perhaps as fast as your hair grows. When hotter than its surroundings, hot rock rises because it is less dense than adjacent material, just like a hot air balloon rises in cool air. A rising column of hot mantle rock is called a “plume. “ If the hot rock reaches the bottom of one of the Earth’s plates it can break through, causing a volcanic eruption and the construction of a volcano. This type of volcano is called a hotspot and many hotspots are thought to be the result of a plume. Since the Earth’s plates are moving, the plate will carry a hotspot volcano away from the source, but then a new volcano forms at the hotspot. After time, a line of volcanoes will result (Figure 1). The oldest volcano will be farthest from the hotspot because it has had the most time to be carried away. This hotspot explanation was cooked up by famous geophysicists J. Tuzo Wilson in the 1960s and W. Jason Morgan in the early 1970s. For many years, geologists consider this simple explanation to be the correct one for linear volcanic seamount chains and the question was considered settled. However, within the past decade, many scientists have begun to question the hotspot explanation as new data have not fit the simple explanation. For some discussion about mantle plumes and other explanations for hotspots, see the Mantle Plumes web site (http://www.mantleplumes.org). Figure 1. Formation of the Hawaiian Islands by the drift of the Pacific plate over a rising thermal diapir (hotspot).
			High.Seas.HIGHTECH/ analyze!ocean@voyages, by lots of us... How to Become a Captain, by the Captain The Search for the Indo-Pacific Humpback Dolphin, by Leslie Nemazi. Rocks Rock! (or ) The Fresh Cut Surface of Beautiful Ocean Rock, by Evelyn Mervine Exploring the Bridge of the RV Roger Revelle Dredging Operations onboard the R/V Revelle, by Amy Eisin Geochemistry of Volcanic Rocks, by Fred Frey Cool Expedition Discoveries Already!, by Will Sager Anatomy of a Seamount Survey, by Will Sager M agnetometers (“Maggie”) and Attracting Sharks, by Rory Wilson Acoustics: Substitute for Superman Vision?, by Will Sager What is Bathymetry?, by Will Sager Hotspots and Ninetyeast Ridge: What’s a hotspot?, by Will Sager