Earthquakes
Where is it
located?
How does it
form?
How does it
change the
Earth’s
surface?
Volcanoes
Mountains
Sea Floor
Spreading
Earthquakes
Where are earthquakes located?
Most earthquakes happen around the edges of the Pacific Ocean or near mountainous areas
such as the Himalayas. Earthquakes, like volcanoes are found along the edges of the Earth’s
plates.
How does an earthquake form?
Earthquakes happen where two of the Earth’s plates meet, or collide. The constant pressure of
the plates pushing against each sometimes builds to a breaking point, when one snaps, and
suddenly causes the ground to move forward. Shock waves from this ground movement cause
the earth to shake, or quake. The ground shakes violently and huge cracks may appear. An
earthquake begins beneath the ground at the point where rocks move. The movement creates
waves of energy which travel up to the surface.
Transcurrent Fault
Profile of an earthquake
The point where the earthquake begins underground is called the focus. The point on the surface
above the focus is called the epicenter. There may be lots more minor earthquakes called
aftershocks after the first earthquake.
How do earthquakes change the Earth’s surface?
Earthquakes may cause structures such as buildings and bridges to fall. They can also trigger
mudslides and avalanches. Earthquakes in the ocean can cause giant waves or Tsunamis to
crash in to the shore, changing the shoreline.
Volcanoes
Where are volcanoes located?
Volcanoes occur where hot liquid reaches the surface through cracks in the Earth’s crust. Most
volcanoes are found where two plates are pushing against one another or moving apart.
Volcanoes that erupt are called active. Many of them are found in areas
around the Pacific Ocean called the “Pacific Ring of Fire.
How does a volcano form?
Pressure builds up underground and pushes molten liquid rock up from a chamber beneath the
surface. It spews out of a crack in the ground as lava.
How do volcanoes change the Earth’s surface?
Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches, falling ash
and floods. Volcano eruptions have been known to knock down entire forests. An erupting
volcano can trigger tsunamis, flashfloods, earthquakes, mudflows and rock falls. More than 80
percent of the earth’s surface is volcanic in origin. The sea floor and some mountains were
formed by countless volcanic eruptions. Gaseous emissions from volcanoes formed the earth’s
atmosphere.
Mountains
Where are mountains located?
Mountains are rock masses that are at least 2,000 feet high. They are found all over the world.
They cover about one quarter of the Earth’s land surface. With the exception of a few isolated
peaks, most of the Earth’s mountains are part of mountain ranges.
How does a mountain form?
There are four different types of mountains. Each one is formed in a different way.
Fold
They are formed when two plates collide
head on, and their edges crumbled,
much the same way as a piece of paper
folds when pushed together.
Volcanic
A volcanic grows when lava
dust and ashes gradually builds
in a cone shape.
Fault Block
They are formed when the faults move
some blocks of rock up while others
are moved down.
Dome Mountain
Dome type mountains are made
when hot magma rises up from
deep in the Earth and pushes the
rocks above into a dome shape.
How do mountains change the Earth’s surface?
Mountain belts that are adjacent to active, convergent plate boundaries are still growing,
as evidenced by active volcanoes, frequent earthquakes, and measurable changes in
elevation. Geologic features such as folds, faults, and igneous rocks remain in place
long after the period of active mountain building that formed them has ended. How are
mountains formed, and what is the connection with earthquakes? The answer may lie
in the fluid-like properties of the Earth’s outer layers. According to a new theory,
mountains may flow up or down when continents collide, in the process; they affect the
circulation of the planet’s atmosphere and change the climate.
Sea Floor Spreading
Where is the location of sea floor spreading?
The Earth’s crust is made up of plates. Both the continents and ocean floors move as
part of these plates. Most plates move apart beneath the oceans. Usually, in the ocean
the floor is moving in different directions in different places.
How does sea floor spreading happen?
During ocean-floor spreading, hot magma from the mantle fueled by convection
currents, pushes up through the cracks between the oceanic plates. As the molten rock
comes up, it spreads. Then it cools and fills in the gap between existing plates. The
cooled rock will later be forced to spread apart by new magma forcing its way upward.
How does sea floor spreading change the Earth’s surface?
Where sea floor spreading is happening, a mountain range forms underwater. This is
because the Earth’s plates are pulling apart. The build-up of new plate material forms
underwater ridges along the boundaries of the plates. A mountain range like this runs
down the middle of the Atlantic Ocean and is called the Mid-Atlantic Ridge.