lecture 8 - volcanoes

Question 1

volcanoes

Answer 1

most located near plate boundaries

approx 65% located along the ring of fire, surrounding the pacific ocean

subduction zones and mid ocean ridges allow molten rock to reach the surface

Question 2

2 types of molten rock and where are they found

Answer 2

magma - found deep within crust and upper mantle

lava - found flowing from an erupted volcano

–> lava is magma on the earths surface

Question 3

what is magma

Answer 3

The most abundant elements in magma are silicon and oxygen; when combined it is referred to as silica.​

Volcanic rocks are named based on the amount of silica present.

Question 4

Types of volcanic rocks:

Answer 4

basalt, andesite, dacite, rhyolite

Low silica <—————-> high silica

Question 5

Viscosity:

Answer 5

Definition:

The resistance to flow

An everyday liquid that has a high viscosity: syrup

Magma also contains small amounts of gases (water vapour and carbon dioxide).

Volcanoes have different shapes based on the chemistry and viscosity of their magma.

Magma viscosity is determined by silica content and temperature.

Question 6

Magma and silica content

Answer 6

Magma with high silica content:

Cooler, more viscous, more gases

Magma with low silica content:

Hotter, less viscous, fewer gases

Volcanoes with high silica magma produce the most explosive eruptions.

As magma approaches the surface, the pressure lowers allowing gases to bubble up and escape.

This is a clue of a pending eruption.

Question 7

magma

Answer 7

Rhyolitic and dacitic magmas produce explosive eruptions.

Basaltic and andesitic magmas produce eruptions that tend to flow rather than explode.

Cooler temperatures: not as much rock, not as runny or not as much liquid.

Question 8

4 types of volcanoes

Answer 8

The classification is based on their shape, appearance, and style of eruptions.

Types of volcanoes:

Shield

Composite

Volcanic dome

Cinder cone

Question 9

Shield volcanoes:

Answer 9

These are the largest volcanoes on Earth and are shaped as broad arcs (like warrior shields) built from lava.

Very liquid like but it hardens in that shape

They are associated with basaltic magma

Eruptions are non-explosive and consist of gentle flows.
Some eruptions can contain tephra.

Accumulations of tephra are referred to as pyroclastic deposits.

If compacted together, these deposits are called pyroclastic rocks.

These volcanoes are common in Hawaii, Iceland and around the Indian Ocean.

Question 10

tephra

Answer 10

fragmented material blown out during an eruption.

Question 11

Composite volcanoes:

Answer 11

These volcanoes are cone-shaped and are built from a combination of lava flows and pyroclastic deposits.

Typical thinking when we think of a volcano.

They are also called stratovolcanoes; this term comes from the layers of lava and deposits.

Question 12

Composite volcanoes:

Answer 12

Eruptions are more dangerous and explosive but less frequent than shield volcanoes.

These volcanoes are common along the west coast from Alaska to Northern California.

Question 13

Volcanic domes:

Answer 13

These volcanoes contain highly viscous rhyolite magma.

They are steep-sided mounts that form around vents.

Question 14

Maars:

Answer 14

Definition:

A circular volcanic crater produced by an explosive eruption and filled with water.

They are caused by groundwater encountering magma creating an explosion.

Maar derives from the Latin mare meaning sea and resembles a large lake

Question 14

Cinder cone volcanoes:

Answer 14

These are relatively small volcanoes composed of small pieces of tephra.

Small, found in Mexico or central America

They are round to oval-shaped and typically contain a crater at the top.

These volcanoes are found in Mexico.

Question 15

Caldera:

Answer 15

A circular to oval depression formed during the collapse of a volcano.

They can be up to 25km in diameter.

Eruptions that form calderas are the largest and most deadly eruptions on Earth.

Question 16

Volcanic vent:

Answer 16

An opening on the surface through which lava and pyroclastic debris erupt.

Most vents are circular, but some are elongated cracks called fissures.

Question 16

Ice-contact volcanoes:

Answer 16

Some volcanoes erupt beneath or against glaciers.

These eruptions melt huge quantities of ice producing floods known as jökulhlaups (means glacier)

When lava contacts glaciers, it quickly cools to form pyroclastic rock.

Ice-contact volcanoes are found in Iceland and British Columbia

Evidence of the Mt.Garibaldi eruption 12,000 years ago in British Columbia is preserved in currently exposed rock.

Question 17

Crater:

Answer 17

A depression formed by the explosion of a volcano top. They can be up to 2km in diameter.

Question 18

Formation of calderas:

Answer 18

Calderas: form by the collapse of a magma chamber below a composite volcano during an explosive eruption.

If it’s a wet climate it will fill in forming what looks like a small lake or pond.

Question 19

Hot springs and geysers:

Answer 19

Groundwater that boils in an underground chamber to periodically produce a release a steam or water is called a geyser.

Heated groundwater can discharge at the surface as a hot spring.

There are approximately 1000 geysers on earth and nearly half are in Yellowstone National park.

Question 20

Old faithful:

Answer 20

This is the most famous geyser in the world.

It erupts to a height up to 50 m with eruptions lasting for 2-3 minutes.

The average interval between eruptions is 70 minutes (+ or - 10 mins)

Question 21

Super eruptions:

Answer 21

These are products of super volcanoes and are extremely rare events.

They occur when a large volume of magma rises to shallow depths in the continental crust over a hot spot.

The magma is unable to break through the crust; pressure builds until the crust can no longer contain it and it breaks through.

A massive amount of land was covered by ash fall from super eruptions.

Question 22

Yellowstone super volcano:

Answer 22

Yellowstone National Park sits on a massive caldera created from the last eruption of the Yellowstone super volcano.

The area is located over a continental hot spot.

Super eruptions occurred 2.2 millions of years ago, 1.3 millions of years ago , and 640,000 years ago.

Earthquakes in the park are monitored continuously.

A super eruption could last for weeks and spread ash over half of the U.S. ash fall would be over 1000 times that released by Mt. St. Helens.

Millions of people would die from ash suffocation and the U.S. agriculture economy would be destroyed.

Question 23

Volcanoes in Canada:

Answer 23

They are generally restricted to British Columbia and southern Yukon.

Mt. Baker in Washington state provides the greatest actual risk to Canada.

Question 24

Mt. Baker:

Answer 24

An eruption of Mt. Baker would eject large amounts of ash over a densely populated region of Canada.

It would also cause landslides and melt glaciers thus causing floods and lahars

Question 25

Effects of volcanoes:

Answer 25

On average, 50 to 60 volcanoes erupt each year.

Over the past century, 100,000 people have been killed by eruptions. Powerful eruptions can impact global climate.

Ash and gases reflect solar radiation causing a cooling.

Question 26

Notable eruptions impacting climate:

Answer 26

Mt. Tambora (1815) Indonesia 1816 is known worldwide as “the year without a summer”

Mt. Pinatubo (1991) Philippines 1992 is one of the coolest years worldwide in the 20th century.

Question 27

Lava flows:

Answer 27

These occur when magma flows out of a central crater or a fissure on the side of a volcano.

Question 28

Pahoehoe basaltic lava:

Answer 28

Lower viscosity ( a few km per hour) high temperature when hardened, it has a smooth texture.

Question 29

Aa basaltic lava:

Answer 29

High viscosity ( a few meters per day), lower temperature.

When hardened it has a blocky texture

There is rock mixed into it

Question 30

Lateral blasts:

Answer 30

An eruption directed away from a volcano where materials are blown parallel to the surface.

Horizontal

Example: a lateral blast from Mt. St. Helens flattened forests for over 20km

Question 31

Pyroclastic flows:

Answer 31

Pyroclastic flows are avalanches of ash, gas, and rock fragments that travel down the slopes of a volcano during an explosive eruptions. (pyro = fire) (clastic = debris)

Speeds can reach 150km’h and the flow can travel up to 30 km from the source

More people have been killed by pyroclastic flows than any other volcanic phenomenon.

Question 32

Ash fall:

Answer 32

Particles of ash can be carried downwind hundreds of kilometres from an eruption site.

Hazards of ash fall:

Destroys vegetation

Contaminates surface water

Health hazards to people and animals

Causes aircraft engine failure

Question 33

Poisonous gases:

Answer 33

Volcanoes emit numerous gases at high quantities.

Eruptions containing sulphur dioxide can burn holes in leaves and lead to the formation of acid precipitation.

A type of smog known as vog can be produced; this can induce asthma attacks and respiratory problems

Vog: like a haze or smoke

High amounts of carbon dioxide released at once can kill animals and vegetation.

Question 34

Sector collapse:

Answer 34

The flank of a volcano can collapse at any time.

Kind of looks like a landslide. Can cause a tsunami

As magma travels up the channel, the volcano can inflate, and its slopes can become over-steepened.

Question 35

Lahar:

Answer 35

Definition: a large amount of material that has become saturated with water and moves downslope. It is an Indonesian word.

Its a mud flow

Lahars are also referred to as mudflows.

Question 36

Mt. St. Helens:

Answer 36

Before its eruption, the volcano had been dormant for 120 years.

In march 1980, small explosions were evident due to groundwater contacting magma.

A bulge began growing on the flank of the mountains. On may 18, 1980, a M 5.1 earthquake caused the area of the bulge to break off and fall downslope.

A lateral blast occurred from that area of the farmer bulge and the entire north slope was destroyed.

Ash was ejected from the central crater, reached heights of 19km, and travelled around the world.

It killed 57 people, mainly from pyroclastic flows.

Question 37

Natural service functions:

Answer 37

Ancient volcanoes provided the gases that now form the atmosphere and sustain life on earth.

Internal heat from volcanoes can produce renewable geothermal energy.

Volcanic soils can be good for agriculture since they are porous, well-drained, and contain nutrients.

Question 38

Minimizing the volcanic hazard:

Answer 38

An eruption forecast is a statement of the probability that a volcano will erupt within a defined time.

Forecasts are based on information provided by:

Monitoring seismic activity.

Shallow earthquakes can precede eruptions

Short warning times from this information for a concern, if we get any warning at all

Thermal and hydrologic monitoring

An accumulation of magma changes properties of the rock and soil

Increased heat may also melt snow or glaciers

Land surface monitoring

Involves monitoring for growth of bulges, swelling and opening of cracks

Monitoring volcanic gas emissions

Increases in carbon dioxide or sulphur dioxide may indicate magma is moving toward the surface

Understanding local geologic history

Mapping of volcanic rocks

Dating of pyroclastic deposits