1.3 Outline

1. 1.3 Outline Plates Move Apart

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

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

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

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

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