Earthquakes and volcanoes

WHAT ARE EARTHQUAKES?

•What causes walls and buildings to crumble during an earthquake?

•The ground trembling

•Based on what we have learned, what might make the ground move?

•The shifting of a tectonic plate or plates

EARTHQUAKES

•An earthquake is a sudden movement of Earth’s crust.

•Usually when layers of rock that are stuck together suddenly slip, an earthquakeoccurs.

•The place where the slipping begins is called the earthquakes focus. Wave of energyripple outward from the focus. When they reach the surface of the Earth, the wavesspread out from a point directly above the focus. This point is the earthquake’sepicenter.

•Due to the pressure from the movement of the tectonic plates pushing on nearbyfaults, earthquakes happen along the boundaries of these plates.

WHY ARE THERE FEWER EARTHQUAKES IN THE CENTER OFTHE UNITED STATES THAN ON THE WEST COAST?

•The center of the United States is farther from aplate boundary.

HOW DOES THE LOCATION OF VOLCANOESCOMPARE TO THE LOCATION OF EARTHQUAKES?

•Most earthquakes and volcanoes are locatednear plate boundaries.

WHAT WOULD HAPPEN IF YOU PUT YOUR HAND IN A PONDAND THEN SHOOK YOUR HAND BACK AND FORTH?

•Waves or ripples would spread from your hand out into the water.

•During an earthquake, Earth’s crust shakes back and forth producing similar waves.

•In the pond, what do the waves travel through?

•Water

•What do earthquake waves travel through?

•The layers of the Earth

TYPES OF WAVES PRODUCED BY ANEARTHQUAKE

•Earthquakes produce three different types of waves.

•These waves are:

•Primary waves – P waves

•Secondary waves – S waves

•Surface waves – L waves

•Fastest

•Pass through both solid and liquid layersof Earth

•Move back and forth as rocks squeezetogether and spread apart

PrimaryWaves

P Waves

•Travel about half as fast as primary waves

•Only move through Earth’s solid layers

•Move up and down

SecondaryWaves

S Waves

•Slowest moving waves

•Travel along earth’s surface like wavesacross an ocean or ripples across a pond.

•Cause the most damage!

SurfaceWaves

L waves

HOW DESTRUCTIVE IS AN EARTHQUAKE?

•Earthquakes vary in the amount of energy they release.

•The strength of an earthquake can be measured in different ways – Magnitude and theextend of damage caused to an area.

The Richter Scale

•The Richter scale measuremagnitude at the epicenter.

•It rates earthquakes fromweakest to strongest. The ratingstarts at 1 which is the weakest.

•Based on mathematics

•More reliable than Mercalli scale

•The Mercalli Scale

•The Mercalli scale, measureswhat people felt and whathappened to objects at specificlocation when an earthquakeoccurs.

•This scale rates earthquakesusing Roman Numerals from I toXII. XII is the most severe.

•Based on observations notmathematics.

•Less reliable than Richter scale

MEASURE OF EARTHQUAKES

•Richter Scale

•Mercalli Scale

CAN PEOPLE PREVENT EARTHQUAKES?

•No, people can’t prevent earthquakes.

•What can people do in earthquake prone areas to provide protection?

•Design buildings with shock absorbers.

•Build highways with special reinforced columns.

DURING AN EARTHQUAKE, A REFRIGERATOR MOVES, ANDPICTURES FALL OFF THE WALL. HOW STRONG IS THEEARTHQUAKE?

•This earthquake is about VI on the Mercalli scale and about 5 or6 on the Richter scale.

WHY IS IT USEFUL TO HAVE TWO SCALES FORMEASURING EARTHQUAKES?

•The Richter scale measures the energy of anearthquake but not the damage it causes. Earthquakeswith the same energy can have different effects,depending on the rock types or other factors in an area.

WHAT ARE VOLCANOES?

•A volcano is an opening in the Earth’s crust. They form on landand on the ocean floor.

WHAT HAPPENS WHEN A VOLCANO ERUPTS?

•Melted rock rises out of the ground.

•What would have to be present for an eruption to occur?

•Melted rock just below the surface and enough pressure below the meltedrock to push it to the surface.

THE RING OF FIRE

•The Ring of Fire is a circle of volcanoes that surrounds thePacific Ocean.

VOLCANO ERUPTION

•An eruption is an outpouring of melted rock, ash, gases, or a combination of these.

•Scientists have concluded that volcanoes tend to erupt when one plate is pushed underanother plate.

•As plates are pushed down into the mantle, they melt. This forms magma. This magmapools in a chamber under the crust.

•Magma may rest for years and years. A crack can form above the chamber or thepressure in the chamber can increase to a point that the magma will rush up toward theEarth’s surface.

•Once magma reaches the surface of the Earth, it is known as lava.

VOLCANO VENTS

•All volcanoes have at least one vent. This is an opening.

•Lave, ashes, and gases erupt through vents.

•A cup can form around a vent. This is a crater, a depression. These are generally found atthe top of a volcanic mountain.

ACTIVE AND DORMANT VOLCANOES

•A volcano that is erupting or has recently erupted is known as an activevolcano.

•A volcano that does not erupt for some time is known as a dormant volcano.

•A volcano that stops erupting is called a dead or extinct volcano.

CALDERA

•A caldera is a hole that forms when a volcano collapses into itself from amagma chamber that has emptied.

WHAT CAN YOU INFER FROM THE RING OF FIRE MAP ABOUTVOLCANO AND TECTONIC PLATE LOCATIONS.

•In the Pacific Ocean, volcanoes are most likely to be found nearthe boundaries of tectonic plates.

WHAT MAKES A VOLCANO MORE LIKELY TO ERUPT WHEREONE PLATE SLIDES UNDER ANOTHER PLATE THAN WHERETWO PLATES COLLIDE?

•When two plates collide, the rocks are driven up into Earth’scrust, not down toward the hot mantle. When one plate slidesunder another, the rocks are driven down, melt, and formmagma that can rise upward into a volcano.

HOW DO VOLCANOES BUILD LAND?

•Lava eventually cools into new rock which changes the landform around it.

•How can magma change a landform wthout reaching the surface?

•Magma can push up the rock above, which then forms a mound. It also cancool below the surface and become exposed when the surface rock erodes.

PARTS OF A VOLCANO

•A dike forms when magma harden in vertical or nearly vertical cracks.

•A sill forms when magma hardens between horizontal layers of rock.

•A laccolith is a dome that can form when magma pushes into a sill anddoes not spread horizontally, but instead pushes upward.

•A batholith is huge and irregularly shaped. It reaches deep within thecrust.

HOW VOLCANOES FORM

•Shield volcanoes are built by thinner,fluid lava that spreads over a largearea. They have a broad base andgently sloping sides.

•Cinder-cone volcanoes are built bythick lava that is thrown high into theair and falls as chunks or cinders.They form a cone shape with a narrowbase and steep sides.

•Composite volcanoes are built bylayers of ash and cinders sandwichedbetween layers of hardened lava.

HOW DO VOLCANOES BUILD ISLANDS?

•80 percent of volcanoes are underwater.

•What happens when a volcano forms underwater?

•As soon as the lava emerges from the vent, it is cooled by water and forms rock.

•What would happen if an underwater volcano kept erupting again and again?

•The mound of lava would grow taller and taller.

WHAT INFORMATION DO YOU NEED IN ORDER TODETERMINE IF ISLANDS FORMED FROM A HOT SPOT?

•You would need to know whether all the islands formed from volcanoes, ifany of the islands had an active volcano, and the ages of the islands todetermine if the extinct volcanoes were moving away from the activevolcano, which is where the hot spot would be.

HOW CAN YOU DISTINGUISH BETWEEN ANISLAND ARC AND AN ISLAND CHAIN?

•The location of the islands in relation to the ocean floor plates will helpdetermine whether it is an island arc. If the islands were formed by hot spots,look for patterns in the direction and ages of the islands compared to themovement of the ocean plates.