VOLCANOES AND EARTHQUAKESCaribbean Studies

Objectives To explain what are earthquakes and

volcanoes To identify major area of earthquake and

volcanic activity. To assess the positive and negative

effects of earthquakes and volcanoes.

What are Earthquakes? The shaking or trembling caused by the

sudden release of energy Usually associated with faulting or

breaking of rocks Continuing adjustment of position results

in aftershocks

Anatomy of an Earthquake Focus (or hypocentre): the center of

energy release. Epicentre: the point on the ground

surfaceimmediately above the focus (closest point on the surface to the focus).

Two kinds of waves from earthquakes

• P waves (compressional) 6–8 km/s.Parallel to direction of movement (slinky), also called primary waves. Similar to sound waves.

• S waves (shear) 4–5 km/s. Perpendicular to direction of movement (rope); also called secondary waves. Result from the shear Strength of materials. Does not pass through liquids.

Tectonic activity in the Caribbean

The amount of damage created by an earthquake depends on several factors. The earthquake’s strength The kind of rock and soil that underlie an

area The population of the area The kind of buildings in the area The time at which the earthquake occurs

Seismologists Seismologists study earthquakes. They

can determine the strength of an earthquake by the height of the wavy line recorded on the paper.

The seismograph record of waves is called a seismogram.

The Richter scale is used to calculate the strength of an earthquake.

Intensity and Magnitude of Earthquakes

Magnitude Often measured using the Richter scale Based on the amplitude of the largest

seismic wave Each unit of Richter magnitude equates

toroughly a 32-fold energy increase

Intensity and Magnitude of Earthquakes

Intensity• A measure of the degree of earthquake

shaking at a given locale based on the amount of damage

Most often measured by the Modified Mercalli Intensity Scale

What are volcanoes

?

What is a Volcano? A volcano is a weak spot in the crust where

molten material comes to the surface Magma reaching the surface is called lava. A volcanic eruption is the process wherein

volcanic materials such as lava, fragmented rocks or gases are emitted or ejected through a crater, vent or fissure on to the earth's surface to form new deposits.

Volcanic Terms A volcano not known to have erupted

within modern history is classified as an extinct volcano.

A volcano that has been known to erupt within modern times but is now inactive is classified as a dormant volcano.

An active volcano is one that erupts wither continually or periodically

Structure of volcano

Where do volcanoes occur? Volcanoes occur most frequently at plate

boundaries. Some volcanoes, like those that form the

Hawaiian Islands, occur in the interior of plates at areas called hot spots .

The greatest number of volcanoes occur on the ocean floor along spreading ridges.

Over 80% of those on land occur at edges of continents, or subduction zones, where one plate dives, or subducts, under another plate.

Why do volcanoes occur?Temperatures in the mantle are hot enough to melt rock into magma magma.•Less dense than the solid rock around it, magma rises and some of it collects in magma chambers magma chambers.•As the magma rises, pressure decreases allowing trapped gasses to expand and propel the magma through openings in the Earth’s surface causing an eruption.

What causes volcanoes?

What causes volcanoes?Hot Spots

Types of VolcanoesShield volcano

Cinder cone volcano

Composite volcano

What Erupts from a Volcano?Pyroclastic material

• Rock fragments created by eruptions

• magma explodes from volcano and solidifies in the air

• existing rock is shattered by powerful eruptions

Volcanic blocks

Volcanic bombs

Lapilli

Volcanic ash

Volcanoes in the Caribbean

QUESTIONS