9. Seafloor Spreading
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Harry Hess was the first person to come up with an explanation for the mid-ocean ridges -- he suggested that the seafloor was created by volcanism within the rift valley along the axis of the ridge. With time the seafloor and underlying crust will spread away from the ridge in opposite directions on either side -- thereby creating a mobile seafloor -- like a conveyor belt -- very interesting idea, which he called seafloor spreading.
As the seafloor spreads apart -- molten rock from mantle convection rises to fill the void -- thus creating volcanoes in the rift valley.
Besides providing information on the shape of the seafloor, with its ridges, volcanoes and flat plains -- oceanographers also towed magnetometers behind their ships to measure the variations in the strength of magnetic properties of the Earth from region to region. Back on shore, they could separate out the portions of the measurement that are associated with the earth's magnetic field from the part that is due to the magnetic properties of the ocean crust -- the rocks had a magnetism too!
By mapping the patterns of magnetism locked in the oceanic crust, they found some very, very interesting patterns...a pattern of stripes that were parallel with the trend of the ridge. The pattern of stripes on one side of the ridge was a mirror image of that observed on the opposite side of the mid-ocean ridge -- these stripes have been given the names "marine magnetic anomalies" -- check your dictionary for the meaning of the word "anomaly."
Created By:
Don Reed
Dept. of Geology
San Jose State University
©Copyright 2008
Last Updated on
Sept. 22, 2008
Seafloor spreading was a concept first described by Harry Hess to explain:
a) the deep sea fishing fleets
b) the place of humans in the sea
c) the occurrence of active volcanoes along the length of mid-ocean ridges
d) a new type of WWW site