Transcript Puerto-Rico Trench

World Earthquakes
Earthquakes outline plates
• Looking at the pattern of major worldwide
earthquakes over the past century shows a
pattern.
• Earthquakes are concentrated into areas called
“earthquake zones” and most of these zones
form bands or lines.
• Scientists came to realize that these bands
represent divisions in the lithosphere and
separate it into pieces (plates).
Plate boundaries
• These divisions within the lithosphere are
called “plate boundaries”. It is here that
plates interact with each other, resulting in
major geologic change, features, and
events.
• Plates may interact in 1 of 3 ways:
– Collide , divide (separate), or slide
(horizontally past each other).
Plate movement
Types of Plate Boundaries
DIVERGENT
CONVERGENT
Convergent (compressional)
boundaries
• Plates collide along convergent
boundaries.
• The results of this interaction depends on
the types of crust collidiing.
• Collision zones form where continents
collide with other continents.
• Subduction zones form where continents
collide with ocean crust or ocean crust
collides with other ocean crust.
Collision zones
• The worlds largest mountain ranges are
formed from colliding landmasses.
• Continental crust cannot sink into the
mantle, so the only place to go is up. Here,
the crust buckles, fractures, and thickens
to form huge mountains.
• The fracturing of the crust creates frequent
and sometimes violent earthquakes.
plate animations site: collision zone
Convergent (cont-cont)
{violent earthquakes; fold
mountains}
The Himalayas
Subduction zones
• Formed by the collision of oceanic crust
with either continental or oceanic crust.
• Ocean crust is dense enough and thin
enough to be “dunked” back into the
mantle where it collides with less dense
crust.
• This process of ocean crust being
absorbed back into the mantle is called
subduction.
Trenches
• A trench is a deep, V-shaped crevice
(canyon) on the sea floor.
• They are created during subduction where
the edges of the plates bend downward.
• They mark the location of a convergent
boundary.
Convergent Boundaries
Convergent (oceanic-continental)
{violent earthquakes & volcanoes}
Peru-Chile Trench
Aleutian Trench
Puerto-Rico Trench
Volcanoes
• Some of the world’s most violent
volcanoes form in subduction zones,
usually as a part of an extended range of
mountains and volcanoes called a volcanic
arc.
• These are sparked off by the melting of
rock as a plate subducts, heats up, and
partially melts.
Convergent (oceanic-continental)
{violent earthquakes & volcanoes}
Convergent (oceanic-oceanic)
{violent earthquakes & volcanoes}
Divergent Boundary
• Plates separate (divide) along a divergent
boundary.
• Most divergent boundaries are on the sea
floor in the form of mid-ocean ridges.
• Some form on land in the form of wide rift
valleys (Iceland, Eastern Africa). Over time
the land splits and a new sea forms.
• Volcanic eruptions and earthquakes are
common along these boundaries.
Divergent boundary
{rift valley, mild earthquakes/
volcanoes}
A Rift Valley
Transform Boundary
• Plates slide past each other without much
of a collision.
• A large crack (called a fault) come to the
surface, known as a transform (or strikeslip) fault.
• Motion along the fault generates frequent
and sometimes severe earthquakes.
• The San Andreas fault in California is an
example.
Transform boundary
{strike-slip faults, earthquakes}
On the Web
• Plate Boundaries RAP
• Musical overview