Earthquakes

An earthquake is the shaking and trembling that result from the sudden movement of part of the Earth’s surface.

only about 20 of them cause significant Scientists estimate that more than a million earthquakes occur each year, but only about 20 of them cause significant damage.

What causes earthquakes? Most earthquakes happen at Faults. Faults are breaks in the Earth’s crust where the surrounding rock has moved or shifted.

Earthquakes usually occur at faults that are along plate boundaries. The plates of the Earth push together, pull apart, or slide past one another.

As these plates move, they put pressure on themselves and each other. When the forces get great enough, the crust is forced to break.

What causes earthquakes? Face partners, Beginning with A What causes earthquakes?

The stress is released as energy moves through the Earth in the form of waves, called seismic waves.

Where do earthquakes occur Where do earthquakes occur? Almost 80% of the Earth’s earthquakes occur along the Ring of Fire which circles the Pacific Ocean.

Plate movements usually happen far below ground. The point beneath the Earth’s surface where the rocks break is called the focus – the origin of the earthquake.

Directly above this on the Earth’s surface is the epicenter. During an earthquake, the most violent shaking is found at the epicenter.

Earthquakes also occur on the floor of the ocean. These earthquakes often produce giant waves called tsunamis.

A seismograph measures the strength and duration of an earthquake.

The size of the earthquake is called its magnitude.

The strength of the earthquake is rated using a Richter scale.

Round Robin Beginning with #2 What did you learn about earthquakes?

Volcanoes

A volcano is an opening in the Earth’s crust through which steam, lava, and ashes erupt.

When magma (molten rock) gets close to the surface, it collects in magma chambers.

Magma and hot gasses continue to collect in these magma chambers until the pressure gets too great for the chamber to hold any more. Then it erupts.

When magma reaches the Earth’s surface, it is called lava.

Shoulder partner Beginning with B What causes volcanoes?

Where do volcanoes occur? Divergent plate boundaries: the plates of the Earth pull apart

Magma seeps up and fills the gap.

Most volcanoes occur at divergent Plate boundaries. Most of them are Located under the ocean

Convergent plate boundaries: the plates of the Earth come together.

One plate slides under the other (subduction), leaving a gap for magma to leak out

Hot Spots: localized areas of hot, rising molten magma material.

The magma melts away the oceanic crust and erupts to build an active volcanic island

The Ring of Fire surrounds the Pacific Ocean, formed at convergent boundaries. The Ring of Fire has more earthquakes and volcanoes than any other place on earth.

Where do volcanoes occur? Face partners Beginning with A Where do volcanoes occur?

How are volcanoes classified? Active volcanoes: erupt continually or periodically (every once in a while

Dormant volcanoes: have not erupted during modern times, but are now inactive

Extinct volcano: have not erupted within modern history and are not expected to ever erupt again.

Shoulder partners, Beginning with B Explain the 3 Classifications of volcanoes