rift valleygreenspun.com : LUSENET : Introductory Geology, Oswego State : One Thread
I was a little confused with this. Is this explaining how oceans are formed in terms of when the land elongates?
-- Greg Koscielniak (email@example.com), January 29, 2001
A rift valley is an elongate valley (low spot on earth's surface) that formed as a result of blocks of rock sliding downward along faults that formed due to the thinning and stretching of lithosphere at a plate boundary.
Rift valleys can be seen today in places like East Africa, where the continental lithosphere has begun to stretch and rift apart, and Iceland, which sits at the north end of the Mid-Atlantic Ridge (one of the Mid-Ocean Ridges we looked at in class). In Iceland, there are frequent eruptions of lava as molten rock from the asthenosphere works its way upward through the thinned and stretched oceanic lithosphere at this divergent plate boundary. If this volcanic activity were going on beneath the sea, it would create new seafloor. Because plates are moving apart at a divergent boundary, the mid-ocean ridges are places where plates move apart, new seafloor is created, and as a result of all this, the ocean may widen (if there's no subduction occurring somewhere else in the ocean).
Does this help answer your question? Respond to your original question if you still aren't sure, or have related questions.
-- Sharon Gabel (firstname.lastname@example.org), January 31, 2001.