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Earth Quakes and Volcanoes

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Juliet Majestic

on 25 September 2012

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Transcript of Earth Quakes and Volcanoes

Earthquakes and Volcanoes What creates an earthquake? Moving plates
2 plates towards each other, one will slide under
2 plates along faults, more energy released and bigger earthquake Where are they found? Vibrations found at the boundaries of tectonic plates Earthquakes from 1985-1995 How do they occur? As plates move, edges experience pressure
Breaks rock along fault line
Energy released as seismic waves
As waves travel through Earth, they create the shaking we experience Focus -The exact point inside Earth where the earthquake originates Travel? In all directions from the focus
Far below Earth's surface
In the form of waves Greatest damage? Epicenter-point on the surface immediately above the focus
Closest to the focus
Energy of seismic wave decreases as you move away Energy released in an earthquake travels as waves... Longitudinal-originates from the focus, moves faster through rock, first waves to reach the recording stations
Travel by compressing Earth's crust infront of it and stretching the crust behind it
Primary of P waves
Transverse-moves more slowly
Similar to the wave created when a rope is shaken up and down
Secondary of S waves
Surface-result of Earth's mass shaking, causes more destruction than P or S waves
Surface bends and reshapes as it shakes (circular motion) The pendulum remains still while a rotating drum of paper records Earth's movement when the ground shakes Seismology -the study of earthquakes How do scientists study earthquakes? Seismographs to record data
Uses inertia to measure ground motion during an earthquake How does seismology determine the composition of Earth's interior? Velocity of seismic waves vary depending on where waves are measured
Waves change speeds and direction when the density of the material they are traveling through changes
Difference in velocity suggests Earth's interior consists of several layers of different densities A scale that expresses the magnitude of an earthquake Each step represents a 30-fold increase in energy released
An earthquake of magnitude 8 releases 810,000 times as much energy as one of magnitude 4
Cannot predict how severe an earthquake will be Effects and number of earthquakes with varying magnitudes, low magnitudes earthquakes occur frequently What factors determine the severity? 1-Distance between populated areas and the epicenter
2-Type of construction used in area buildings
3-How deep the focus is
4-Softer rock vs. rigid rock
5-Time of the day
6-Soil composition
7-How saturated the ground is What is a volcano? Opening in Earth's crust through which magma has reached Earth's surface
Usually one central vent
Several smaller vents?
Magma reaches surface and turns into lava
From partial melting of mantle rocks
Gas molecules in magma causes it to rise What can form? Hill/mountain
As materials pour/explode from the vents
Release molten rock, ash, and a variety of gases from melting in the mantle/crust Shield Volcano Mild eruptions
Magma rich in iron and magnesium
Very fluid
Forms lava flows great distances
Several times?
Buildup of lava produces gently sloping mountains
Some of the largest volcanoes in the world are shield volcanoes
Mauna Loa in Hawaii
13,000 ft above sea level
9,020 m or 29,500ft above sea floor 75% of active volcanoes on Earth occur along edges of the Pacific Ocean No direct S waves can be detected 105 degrees from epicenter
No direct P waves can be detected between 105 and 140 degrees from epicenter Volcanoes build up into hills or mountains as lava and ash explode from openings in Earth called vents Alternating layers of ash, cinders, and lava
Magma rich in silica
More viscous than a shield volcano's
Gases trapped in the magma
Eruptions alternate between flows and explosive activity
Produces cinders and ash
Thousands of meters high and steeper slopes than shield volcanoes
Mt. Fuji in Japan, Mount St. Helens, Mount Rainier, Mount Hood, and Mount Shasta all in the western U.S.
Seamount/underwater volcanoes erupt violently forms clouds of ash and steam
Looks like composite volcanoes Composite Volcanoes Cinder Cones Volcanoes Smallest
Most abundant
Violent eruptions
When large amounts of gas trapped in magma
Vast quantities of hot ash and lava thrown from vent
Particles fall to ground around vent
Forms a cone
Active for a short time
Then dormant
Paricutin in Mexico
Erupted in 1943
After 2 years cone had grown to 1,480 ft
Eruptions ended in 1952 What causes volcanoes? Plate movement
Common around edges of the Pacific Ocean
Oceanic tectonic plates collide with continental plates
75% located here Ring of Fire Volcanoes around the Pacific Ocean lie in a zone known as the Ring of Fire
A plate sinks at a convergent boundary
Melting in the mantle
Magma rises to the surface
Volcanoes that result form the edges of the Ring of Fire
Tend to erupt...
Clouds of ash and gases
High-viscosity lava makes it difficult for gases to escape
Gas pressure builds up
Causes explosive eruptions Benefits? Forms islands
Fertile land Japan? Types? Japan located in the Pacific Ocean
Around Ring of Fire
More likely for earthquakes
An earthquake was made when plates shifted
Plates in ocean caused tsunami
Japan’s boundary is on the Pacific and the North American Plate
The earthquake created a tsunami
Plates are below water
Vibrations of the plates caused uproar of water
Created giant waves Richter Scale Review Questions 1) In what regions of the world are most earthquakes commonly found?
2) What creates earthquakes?
3) How many types of waves does an earthquake release?
4) How does magma form?
5) Where does magma come from?
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