1.3 Outline Plates Move Apart

I. Tectonic Plates Have Different Boundaries 1) Divergent boundary: occurs where plates move apart; mainly found in ocean 2) Convergent boundary: occurs where plate push together 3) Transform boundary: occurs where plates scrape past each other

II. The sea floor spreads apart at divergent boundaries 1) Rift valley: gap that forms as a result of mid-ocean ridges expanding A. Mid Ocean Ridges and Rift Valleys 1) Mid-ocean ridges, rift valleys and new crust mark where the sea floor spreads apart 2) When molten material rises from the asthenosphere, cold ocean water cools the rock until it becomes solid 3) As the plates move apart, new cracks open in the solid rock

III. Continents split apart at divergent boundaries 1) Like the sea floor, continents also spread apart at a divergent boundary 2) Begins to form when hot material rises from deep in the mantle causing the crust to bulge upward 3) Crust cracks as it is stretched, causing a rift valley to form

III. Continents split apart at divergent boundaries (cont.) 4) Volcanoes form from magma rising through the cracked, thinned crust 5) Thinned valley floor sinks lower until it is below sea level 6) Water from nearby oceans or rivers may fill the valley and form a sea or lake

IV. Hot spots can be used to track plate movements 1) Hot spots: an area where heated rock rises to thin columns (plumes) from the mantle a) Offer a way to measure plate movement, because a hot spot generally stays in one place, while tectonic plate above it keeps moving