GEOS 170A1 Lecture Notes - Lecture 7: Mount St. Helens, Seismic Tomography, Plate Tectonics

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EARTH LECTURE 7
Convergent plates-
Plates move
Plate boundaries=edge of plate
POWERPOINT…..
Lithosphere is destroyed
Subduction zone
Most dangerous volcanoes
Biggest EQs
Ocean trench is dry between plates
Overriding plate dragged down, making trench
Deepest places on earth
Marianas trench
11km
Most dangerous/explosive volcanoes here
Water in subducted plate squeezed out; asthenosphere melts
Mt. st. helens, mt pinatubo, mt vesuvius
Ring of fire is outlined by convergent boundaries
Only oceanic plates subduct
3 types
Ocean to ocean
Subduction
One plate gets pulled under another
Plate boundary>trench
Melt...magma...volcanoes
Ocean to continent
Subduction of plate boundary>trench
Melt...magma...volcanoes
How do we know what it looks like underground-
Seismic tomography
Which plates are actually moving-
Both
But we usually “pin” the upper plate in place bc it kind of looks that way though
they are in fact, both moving
EARTH LECTURE 8
Plate tectonics: convergent PBs-
Third kind: continent to continent
No subduction (both sides too light to subduct)
Big mountains are created (Himalayas)
Continent to continent collision-
Neither plate subducts (both too light)
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