Volcanoes and earthquakes. Caribbean 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?. - PowerPoint PPT Presentation
Text of Volcanoes and earthquakes
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
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
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