Volcanoes are caused by pressure and temperature inside the earth. Volcanoes are mountains that contain molten rock. Molten rock is called magma.
The magma chamber is at the bottom of the volcano. When magma is out of the volcano, it is called lava. When lava gets cold it turns into rock.
There are 3 types of volcano:
Composite – They have steep sides formed from layers of ash and lava.
Shield - These volcanoes have gently sloping sides formed from layers of lava.
Cinder Cone - These have steep sides coming off a circular vent. This forms what looks like a cone.
Mount Vesuvius, in Italy, is a famous volcano. It erupted in AD 79 and completely covered the city of Pompeii.
The earth has several volcanoes. One of the Hawaii Islands is actually a large shield volcano.
A scale called the Moment Magnitude Scale is used to measure the strength of an earthquake.
This is what may happen depending on the scale.
4.0 - Could shake your house as if a large truck were passing close by.
6.0 - Things will fall off of shelves. Walls in some houses may crack and windows break.
7.0 - Weaker buildings will collapse and cracks will occur in bridges and on the street.
8.0 - Many buildings and bridges fall down. Large cracks in the earth.
9.0 and up - Whole cities flattened and large-scale damage.
Earthquakes happen when two large pieces of the Earth's crust suddenly slip. The shock waves shake the surface of the earth.
The largest earthquake was in Chile in 1960. It measured 9.6 on the scale.
Earthquakes can cause huge waves in the ocean called tsunamis.
Earthquakes can happen in any weather. Alaska has the most chance of earthquakes in the world.
In Ancient Greece, people believed that Poseidon, god of the sea, caused earthquakes.
Scientists think that animals may sense weak tremors before a quake.