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The Movement of Earth’s Crust and Earthquakes

Grade 4
Jun 9, 2023

The Moving Crust


You’ve studied that the Earth is made up of layers. The crust is the thin outer layer of the Earth. The mantle is found beneath the crust.

What Causes the Earth’s Crust to Move?

Plates :

The Earth’s surface is divided into several massive rock plates. The crust is used to make plates. The crust is firm. The upper mantle has the capability to flow. The Earth’s plates move when the mantle flows. The plates of the Earth move about as slowly as your fingernails grow. Plate edges are where changes to the crust occur. The majority of the changes are not visible or felt. Others are unmissable!



Some plates slide from one side to the other. A fault is an area where they rub together. A fault is a long, narrow crack in the crust of the Earth.

A plate on one side of a fault can slide up while the plate on the other side slides down. Rising plates can cause fault blocks to form mountains. A plateau may form if the lifting is spread out over a large area. A plateau is a flat-topped high landform.

Fault block mountain


Some plates collide near the edges of continents. A fold forms when the land scrunches up between them. A fold in the rock layers is a bend.

A fold becomes a mountain if the land continues to squeeze. A mountain is a tall landform with a peak. Wind and rain can break off bits and pieces over time.

Fold mountain

Fold mountains can form where plates slide in the direction of each other.

What Factors Cause Earthquakes?

An earthquake is an unexpected tremor (shock) in the Earth’s crust. Plates moving along a fault cause it. When the plates collide, energy is released into the rock. This energy could be stored for many years in the Earth’s crust by rocks.

They suddenly disintegrate! Earthquakes are common in areas where active faults exist, such as parts of Alaska and California.       


How do Earthquakes move?

An earthquake starts beneath the ground. The energy released by a sudden plate movement causes the crust to shake. Vibrations, or waves, move in all directions through the crust.

Have you ever dropped a pebble into the water? An earthquake’s waves travel like water’s ripples. The waves weaken as they move away from the epicenter of the earthquake. Even so, you could feel them hundreds of miles below the surface!

Formation of earthquake

Earthquake Safety

Most earthquakes are too small to be felt. Others can cause significant harm. Buildings and roads may collapse during a major earthquake. Bridges could collapse.

Do you know what to do if the ground beneath you begins to tremble?

Following a few simple rules will keep you safe during an earthquake.

  • If you’re inside, hide under a table or a doorway.
  • Keep your distance from the walls and windows.
  • Stay away from trees, power lines, and anything else that could fall down.
Earthquake safety

Earthquakes in the Ocean

Some earthquakes occur beneath the ocean. An earthquake of sufficient magnitude can cause the ocean crust to lift suddenly. When this occurs, take caution! A massive ocean wave, or tsunami, could hit the shore. Tsunamis are the most destructive along coastlines. They have the ability to destroy everything in their path.


How Do Scientists Investigate Earthquakes?

A vibration can be caused by any movement. Seismic waves are earthquake-induced vibrations. When an earthquake occurs, seismic waves radiate from the epicenter in all directions. The waves move at various speeds.

Some of the waves travel near or along the Earth’s surface. Others journey through the Earth’s interior.

Measuring Seismic Waves  

Seismographs are used by scientists to measure seismic waves. A seismograph is a device that detects and records earthquakes. It depicts seismic waves as curved lines on a graph. The lines indicate how much the ground moves. The steeper the lines, the stronger the quake.         

Chang Heng’s Seismoscope -China
Seismograph was invented in Italy

Seismic Network

When an earthquake occurs, one of the first questions that arise is, “Where was it?” Seismographs are used by earthquake scientists all over the world. They gather information from each seismic station. They then calculate the quake’s location and depth.

Ocean bottom seismometers


A volcano is a mountain that forms around a crack in the Earth’s crust. A volcano will occasionally force materials from the Earth’s interior out of its opening. Scientists refer to this as an eruption.

Melted rock, gases, ash, or small rocks can all be emitted into the atmosphere during a volcanic eruption.

Magma is a rock that has melted. When magma goes to the Earth’s surface, it is called lava. A volcano can build a large mountain by erupting frequently. With each eruption, a layer of lava and ash is added. Lava and ash cool and solidify into rock. Some volcanoes lie dormant (inactive) for many years before erupting violently. Others have erupted frequently in the past but will never do so again.


The majority of volcanoes form at plate boundaries. When two plates collide, one may sink beneath the other. The plate becomes hotter as it sinks. The rock melts and turns into magma. Magma rises to form a volcano.

Volcanoes also form when the Earth’s plates separate. Magma can rise to the surface through the space between the moving plates.

Some volcanoes form far from plate boundaries. These hot spots are located where the Earth’s crust is extremely thin. Magma can easily penetrate the surface. Hawaii’s islands formed over a hot spot in the Pacific Ocean. The islands are the summits of massive volcanoes that erupted from the ocean floor.

The Movement of Earth's Crust


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