Earthquakes and

Volcanos

Earth Science

Mr.McKay

Earthquakes• Earthquake – The shaking and

trembling that results from the sudden movement of part of the Earth’s crust– Pebble in pond– Scientists predict over 1,000,000

earthquakes happen each year– Faulting is most common reason for

Earthquakes• San Andreas Fault

– Fault Video

Tsunamis• Tsunami- A huge wave

caused by an earthquake on the floor of the ocean– They can travel at speeds

of 700 to 800 MPH– They can reach Heights of

20 meters• The height of a 6 Story

Building• Tsunami Off of Thailand• Trouble in Paradise

Seismic Waves• Earthquake waves are

known as seismic waves– Focus- The point beneath

the Earth’s surface where rocks break and move

• The focus is the point of origin for the earthquake

– Epicenter- Directly above the focus on the Earth’s surface

• Earthquake waves reach the epicenter first

• Seismic Waves

Seismic Waves• Primary waves-

– P-waves: Seismic waves that travel the fastest

• They arrive at a given point before any other type of wave

• They travel through– Solids– Liquids– Gases

Seismic Waves• Primary waves-

– They move through the Earth differently depending on the material they are traveling through

– As they move deeper into the Earth, where it is more dense, they move faster

– They are push-pull waves

Seismic Waves• Secondary Waves

– S-Waves – Seismic waves that do not travel through the Earth as fast as P-waves do

– S-waves arrive at a given point after P-waves do– S-waves travel through solids but not liquids and

gases

Seismic Waves

• Surface Waves– L-waves: They are the slowest moving seismic waves

• They arrive at a given point after P and S waves– They start at the epicenter and move along the Earth’s surface– Earth’s surface moves up and down like water waves do– They cause the most damage to the Earth because they bend

and twist the surface

Seismograph• Seismograph – An

instrument that detects and measures seismic waves– Crude Seismographs

around for hundreds of years

– The first practical was made in 1893 by John Milne

– Consists of • A weight attached to a spring

or wire• A pen attached to the weight

that records the movement of the Earth on a paper, that is wound tightly around a constantly moving drum

• Seismologists – Scientists who study earthquakes– PSP Seismograph– They can determine the strength of

an earthquake by studying the height of the waves

• They look at a Seismogram• They match the seismogram to a chart

called the Richter Scale– Invented in 1935– The scale is from one to ten, with any

earthquake above 6 being very destructive

Seismograph

• Formation

• High temperature• High Pressure• Liquid State• Found in pockets called magma

chambers

– Magma constantly moves and works its way through cracks toward the surface by melting the solid rock

Volcanoes

–Magma: Rock deep within the Earth

• Formation– Lava – Magma that has reached

the Earth’s Surface– The place where magma becomes

lava is called a Volcano– The opening through which lava

erupts is called a vent• Volcanoes can have more than one

vent– Lava will poor from the sides of a

volcano as well as the top

Volcanoes

• All are not Alike– Some are quiet

• Lava oozes from a vent

– Others are violent• With lava and other material hurled

hundreds of feet in the air• Gases and earth material mix to be seen

from miles away

– The opening through which lava erupts is called a vent

• Volcanoes can have more than one vent– Lava will poor from the sides of a

volcano as well as the top

– Eruption

Eruptions

• Scientists study the makeup of the lava that spews from the Volcanoes vents to gain knowledge about the interior magma

• Types of Lava– Dark-colored/ Water– Light-colored/ little Water– Chemical composition of both– Large amounts of gases

• Steam and carbon dioxide

Eruptions

Eruptions• During eruptions many rock fragments are blown

into the air– Smallest = volcanic dust– Medium = volcanic ash– Large = volcanic bombs

• Small volcanic bombs the size of golf balls are called Cinders

Types ofVolcanoes

• Different types of volcanic eruptions form different types of volcanoes– Cinder Cones - made mostly of cinders and other rock

particles that have been blown into the air• Form from explosive eruptions• Cones are not high• Narrow base & steep sides

– Shield Volcanoes – composed of mostly quiet lava flows

• Gently sloping, domed shaped mountain forms– Composite Volcanoes – Built up of alternating layers

of rock particles and lava• First is a violent eruption• Then a quiet eruption• After many alternating eruptions a cone shape is formed

Types ofVolcanoes

• At the top of a funnel-shaped pit or depression is a pit– Called Crater

• If it becomes to large it is called a Caldera• Super Eruption• Discovery Channel :: Virtual Super volcano

• Three Major Zones– Nearly all the way around the edge of the

Pacific Ocean• Called the Ring of Fire

– Near the Mediterranean Sea• Called the Mediterranean Zone

– Third Extends through Iceland to the middle of the Atlantic Ocean

• Mid-Atlantic Ridge – Long ridge of volcanoes

Zones