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 earthquake occurs. The place where the slipping begins is called the earthquakes focus. Wave of energy ripple outward from the focus. When they reach the surface of the Earth, the waves spread out from a point directly above the focus. This point is the earthquake’s epicenter. Due to the pressure from the movement of the tectonic plates pushing on nearby faults, earthquakes happen along the boundaries of these plates.

The center of the United States is farther from a plate boundary. Why are there fewer earthquakes in the center of the United states than on the west coast? The center of the United States is farther from a plate boundary.

Most earthquakes and volcanoes are located near plate boundaries. How does the location of volcanoes compare to the location of earthquakes? Most earthquakes and volcanoes are located near plate boundaries.

What would happen if you put your hand in a pond and 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 an earthquake Earthquakes produce three different types of waves. These waves are: Primary waves – P waves Secondary waves – S waves Surface waves – L waves

Primary Waves P Waves Fastest Pass through both solid and liquid layers of Earth Move back and forth as rocks squeeze together and spread apart P Waves

Secondary Waves S Waves Travel about half as fast as primary waves Only move through Earth’s solid layers Move up and down S Waves

Surface Waves L waves Slowest moving waves Travel along earth’s surface like waves across an ocean or ripples across a pond. Cause the most damage! 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 the extend of damage caused to an area.

Measure of Earthquakes The Richter Scale The Richter scale measure magnitude at the epicenter. It rates earthquakes from weakest to strongest. The rating starts at 1 which is the weakest. Based on mathematics More reliable than Mercalli scale The Mercalli Scale The Mercalli scale, measures what people felt and what happened to objects at specific location when an earthquake occurs. This scale rates earthquakes using Roman Numerals from I to XII. XII is the most severe. Based on observations not mathematics. Less reliable than Richter scale

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, and pictures fall off the wall. How strong is the earthquake? This earthquake is about VI on the Mercalli scale and about 5 or 6 on the Richter scale.

Why is it useful to have two scales for measuring earthquakes? The Richter scale measures the energy of an earthquake but not the damage it causes. Earthquakes with 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 land and 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 melted rock to push it to the surface.

The ring of fire The Ring of Fire is a circle of volcanoes that surrounds the Pacific 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 under another plate. As plates are pushed down into the mantle, they melt. This forms magma. This magma pools in a chamber under the crust. Magma may rest for years and years. A crack can form above the chamber or the pressure in the chamber can increase to a point that the magma will rush up toward the Earth’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 at the top of a volcanic mountain.

Active and Dormant Volcanoes A volcano that is erupting or has recently erupted is known as an active volcano. 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 a magma chamber that has emptied.

What can you infer from the Ring of Fire map about volcano and tectonic plate locations. In the Pacific Ocean, volcanoes are most likely to be found near the boundaries of tectonic plates.

What makes a volcano more likely to erupt where one plate slides under another plate than where two plates collide? When two plates collide, the rocks are driven up into Earth’s crust, not down toward the hot mantle. When one plate slides under another, the rocks are driven down, melt, and form magma 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 can cool 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 and does not spread horizontally, but instead pushes upward. A batholith is huge and irregularly shaped. It reaches deep within the crust.

How volcanoes form Shield volcanoes are built by thinner, fluid lava that spreads over a large area. They have a broad base and gently sloping sides. Cinder-cone volcanoes are built by thick lava that is thrown high into the air and falls as chunks or cinders. They form a cone shape with a narrow base and steep sides. Composite volcanoes are built by layers of ash and cinders sandwiched between 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 to determine if islands formed from a hot spot? You would need to know whether all the islands formed from volcanoes, if any of the islands had an active volcano, and the ages of the islands to determine if the extinct volcanoes were moving away from the active volcano, which is where the hot spot would be.

How can you distinguish between an island arc and an island chain? The location of the islands in relation to the ocean floor plates will help determine 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 the movement of the ocean plates.