Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. The motivating force for seafloor spreading ridges is tectonic plate pull rather than magma pressure, although there is typically significant magma activity at spreading ridges. At a spreading center, basaltic magma rises up the fractures and cools on the ocean floor to form new seabed. Hydrothermal vents are common at spreading centers. Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone. Additionally spreading rates determine if the ridge is fast, intermediate, or slow. As a general rule, fast ridges have spreading (opening) rates of more than 9 cm/year. Intermediate ridges have a spreading rate of 5–9 cm/year while slow spreading ridges have a rate less than 5 cm/year.
Lexi is studying seafloor spreading ridges in three different regions of the ocean. She is trying to determine the rate of spread of each region so she can correctly classify each ridge. Based on her data, Lexi has learned that the spreading rate of Region A is 4 cm/year, the spreading rate of Region B is 7 cm/year and the spreading rate of Region C is 12 cm/year.
Is Region C more or less likely than Region A to be a fast ridge?