Earth Science CET (Earthquakes and Volcanoes)

They are vibrations caused by earth movements at

plate boundaries and at major fault lines.

Earthquakes

An unpredictable event in which rock shifts below earth’s

surface, releasing enormous amounts of energy and sending

out shock waves that cause the ground to shake drastically.

Earthquakes

The most severe earthquakes are normally found at:

1. Convergent Boundaries

2. Transform Boundaries

The point within earth where faulting begins

Focus or Hypocenter

The point directly above the focus on the surface

Epicenter

Waves of energy caused by the sudden breaking of rock

within the earth

Seismic Waves

Two Types of Seismic Waves:

1. Body waves

2. Surface waves

Seismic waves are measured using the?

Seismometers

Seismic waves are recorded using?

Seismographs

They travel through the layers of the planet.

Body waves

Two types of Body Waves:

1. P-waves

2. S-waves

Fastest moving waves

Compressional waves

Can travel through solids and liquids

Pushes and pulls the rock it moves through

Primary Waves or P-waves

The second wave you feel in an earthquake

Moves slower than P-waves

Can only travel through solids

Moves up and down or side-to-side

Secondary Waves or S-waves

Effects of Earthquake Hazards:

1. Ground Shaking

2. Tsunami

3. Landslides and Rockfalls

4. Subsidence and Lateral Spreading

5. Liquefaction

If an earthquake generates a large enough shaking intensity,

structures like buildings, bridges and dams can be severely

damaged, and cliffs and sloping ground destabilised.

Ground Shaking

Long wavelength oceanic waves generated by the sudden

displacement of seawater by a shallow earthquake.

Tsunami

Ground shaking due to earthquakes destabilised cliffs and

steep slopes, causing landslides and rockfalls as a

significant side-effect.

Landslides and Rockfalls

Lowering of the ground surface, often

occurs during earthquakes.

Subsidence and Lateral Spreading

Occurs when waterlogged sediments are agitated by

seismic shaking. Buildings can sink down into the ground or

tilt over, while underground pipes may rise up to the surface.

Liquefaction

It is a measure of the energy released at the

source of the earthquake. It is a quantitative measure of the

earthquake's size.

Magnitude

The most commonly used scale for magnitude of earthquakes

Richter scale

The scale more widely used by seismologists because it provides a more accurate representation of an earthquake's

size, especially for large events.

Moment magnitude scale (Mw)

It measures the effects of an earthquake at specific

locations on the Earth's surface, including the severity of

shaking and the damage caused.

Intensity

The most commonly scale used in the United States for intensity

Modified Mercalli

Intensity (MMI)

It is a horseshoe-shaped zone that encircles the Pacific Ocean

basin, characterized by a high level of tectonic activity, including

earthquakes, volcanic eruptions, and mountain-building

processes. It is one of the most geologically active regions on

Earth.

The Pacific Ring of Fire

Phivolcs Earthquake Intensity Scale

It is an opening in Earth’s crust through which molten

rocks, rock fragments, and hot gases erupt. It is a mountain that

forms when magma reaches the surface of the Earth. Magma

ries because it is less dense than the one solid rock around.

Volcano

A volcano is an opening in the earth’s crust where _______ can make its way to the surface.

Molten material

Volcanoes form along where?

Plate boundaries

As an active volcano ages, the vent and the mount it creates

on the earth’s crust become bigger; thus, more lava and

other hot, molten rocks come out of it. This phenomenon is

called?

Volcanoes

Main Parts of a Volcano:

1. Vent

2. Crater

3. Summit

It is the opening from which lava flow. It is

connected to the magma chamber, dust, ash, and rock

particles can also be thrown out the vent.

Vent

The top of the volcano. It is the funnel shaped pit. It

is formed when the matrial explodes out of the vent.

Crater

The top of the volcano.

Summit

Where do volcanoes occur?

Most form along plate boundaries...

In subduction zone

Over hot spots

Where plates are pulling apart

In terms of water vapor, more water means?

Bigger explosion

In terms of trapped gas like water and carbon dioxide, an easy cape (low pressure) means?

Quiet eruption/explosion

In terms of trapped gas like water and carbon dioxide, difficult to escape (high pressure) means?

Explosive/violent eruption

Magma Type:

1. Basaltic (thin) = quiet

2. Granitic/Andesitic (thick) = violent

This refers to molten rock that exists beneath the

Earth’s surface. It is a combination of molten or semi-molten

rock, volatiles (such as water vapor and carbon dioxide), and

solid minerals.

Magma

Once magma reaches the Earth’s surface and begins to

flow, it is termed lava. The emergence happens through volcanic

eruptions or fissures.

Lava

Types of Eruptions:

1. Hawaiian Eruptions

2. Strombolian Eruptions

3. Vulcanian Eruptions

4. Pelean Eruptions

5. Plinian Eruptions

6. Phreatic Eruptions

named after the Hawaiian Volcanoes.

the calmest type of volcanic events.

eruptions often occur at vents around the summit and from

fissure vents radiating out of the center.

Hawaiian Eruptions

named after the volcano Stromboli.

these eruptions are driven by the bursting of gas bubbles

within the magma.

these gas bubbles then turn into gas slugs.

Strombolian Eruptions

named after the volcano Vulcano

highly viscous magma makes it difficult for gases to escape.

The build-up of gas pressure results in an explosive

eruption.

Vulcanian Eruptions

named after the volcano Mount Pelee.

a great amount of gas, dust, ash, and lava fragments are

blown out the volcano’s central crater.

one of the most dangerous in the world, capable of tearing

through populated areas and causing massive loss of life.

Pelean Eruptions

also called Vesuvian.

eruption velocity is controlled by the gas contents of the

column.

Plinian Eruptions

Also called steam-blast eruptions.

When cold ground comes into contact with hot rock or

magma, it superheats and explodes.

Phreatic Eruptions

Types of Volcanoes:

1. Shield Volcanoes

2. Stratovolcanoes (Composite)

3. Cinder Cone Volcanoes

4. Lava Domes (Volcanic DOmes)

5. Calderas

Broad, gently sloping

sides.

Non-explosive

eruptions with fluid,

basaltic lava that flows

easily.

Mauna Loa and Kilauea

in Hawaii.

Shield Volcanoes

Steep, conical profiles.

Alternates between

explosive eruptions with

pyroclastic flows and

quieter lava flows.

Mount St. Helens in the

USA, Mount Fuji in Japan.

Stratovolcanoes (Composite)

Steep, conical hills made of

volcanic debris.

Short-lived, explosive

eruptions that throw

cinders, ash, and volcanic

rocks.

Paricutin in Mexico, Sunset

Crater in the USA.

Cinder Cone Volcanoes

Steep, dome-shaped

mounds.

Slow, viscous lava

eruptions.

Novarupta Lava Dome in

Alaska, Mount St. Helens'

Lava Dome.

Lava Domes (Volcanic Domes)

Large, depression-shaped

features formed by the

collapse of a volcano.

Result from massive,

explosive eruptions that

empty the magma chamber.

Yellowstone Caldera in the

USA, Santorini in Greece.

Calderas