Transcript 1.3 Outline

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