What Happens at the Plate
Boundaries?
(B) seamounts-are underwater mountains. When these have been eroded by waves
and currents to have flattened tops they are called guyots or tablemounts.
(E) Volcanic Islands- are the larger seamounts that actually extend above the surface
of the water.
(D)Rift Valley along a Mid-OceanRidge- is a long continuous chain of mountains
(seamounts) where new seafloor is created with a large crease that is the rift in the
middle.
(F) Continental Shelf- gently sloping shallow area that extends from
the edge of a landmass. Beach and shore areas until it slopes.
(A)Continental Slope- is the area just beyond the shelf where the
seafloor drops steeply. The Drop Off!
Continental Rise- a sediment wedge at the bottom of a slope where
sediment falls and collects. Not found if trench is present.
(C) Abyssal Plane- flat and deep area of the ocean floor just beyond
the slope
(G) Trenches- deep cuts where subduction is occurring.
Submarine Canyon- once an old river delta that is now covered by sea
level that is higher. Named because they hid subs there during WWII.
Three Types of Plate Boundaries
Divergent: Only found on Mid-Ocean Ridge. Produces new seafloor,
deep but usually undetected earthquakes. Small and oozy lava
usually underwater but can be on land.
Denoted by arrows moving apart.
Convergent: When plates collide. If seafloor is made in one area, it
has to be moved and destroyed somewhere else. There are three
types of convergent boundaries. It is denoted by arrows pointing
toward each other.
1. Continent hitting continent- Ex: Asia and India forming great mountains. No
subduction or trench.
2. Continent hitting ocean- ocean basalt is denser than continent granite and goes
down in the earth and melts forming Andesite volcanoes. Very explosive
3. Ocean hitting ocean- older basalt floor is denser and will subduct slowly forming
island arcs or a series of volcanoes and islands. Not as explosive.
Rift Zones (Valley) on Mid-Ocean Ridge
Diverging plates move away from each other very slowly. As they do,
magma rises from the mantle. It pushes up the crust and eventually
breaks through the crust. This process can take place under the ocean
or on land. The magma that quietly bubbles out at rift zones is
generally runny and dense. Each time the magma erupts new crust is
added, creating a ridge of mountains.
Most eruptions happen on the ocean floor and go undetected, quietly
constructing new crust. The thin magma cools quickly and forms
layers of new crust on the sea floor. The convection currents in the
mantle pull the crust in opposite directions at rift zones.
• Turn in Plate tectonics book work
• Get back their plate map so that they can
study for tomorrow. I corrected ones in the
bin but DID NOT TAKE a grade yet. You will
turn in tomorrow.
• Quiz tomorrow JUST naming the plates.
• Pass back papers in Graded bin if time
remains.