Lecture 7 - volcanoes Flashcards
What are the two types of molten rocks
Magma and Lava rocks
Define a Magma rock
It is found deep within the crust and upper mantle
Define a Lava rock
flows from an erupting volcano
Lava is Not Magma on the earths surface? T or F?
False
How are volcanic rocks named
Volcanic rocks are named by the number of silica present.
silica is the combination of oxygen and silicon
List the types of volcanic rocks, ranging from low silica to high silica
- Basalt (lowest silica)
- andesite
- dacite
- rhyolite (highest silica)
What is Viscocity
The resistance to flow
magma viscocity is determined by silica content and temperature
Characteristics of magma with high silica content include?
cooler, more vicious, more gases
high silica magma tend to produce eruptions that explode
List traits of magma with low silica content
hotter, less vicious, fewer gases
low silica magma tend to produce eruptions that flow
What are the four different types of volcanoes
Shield, composite, volcanic dome, cinder cone
How are volcanoes classified?
Though their shape, appearance, and style of eruptions
What are shield volcanoes
the largest volcanoes on earth
- shaped as broad arcs built from lava
- eruptions are non explosive
What is tephra?
Fragmented materials blown out during an eruption
- some shield volcano eruptions contain tephra
Accumulations of tephra are referred to as?
Pyroclastic deposits
Compacted pyroclastic deposits are called?
Pyroclastic rock
Shield volcanoes are common in what places?
Hawaii, Iceland and around the Indian ocean
describe composite volcano eruptions
eruptions are more dangerous and explosive but less frequent than shield volcanoes
Describe volcanic domes
These volcanoes contain highly viscous rhyolite magma
- steep sided mounts that form around vents
What is Cinder Cone Volcanoes
Relatively small volcanoes composed of small pieces of tephra
- round to oval shaped and typically contain a crater at the top
- found in Mexico
What is Maars
A circular volcanic crater produced by an explosive eruption and filled with water
How are Maars caused?
Maars are caused by groundwater encountering magma creating an explosion
What are Jokulhlaups?
Floods produced when volcanoes erupt beneath or against glaciers that melt huge quantities of ice
List the volcanic features
- Crater
- Volcanic Vent
- Caldera
What is Crater?
- A depression formed by the explosion of a volcano top
What is Volcanic Vent
- an opening on the surface through which lava and pyroclastic debris erupt
How are Caldera’s formed
Calderas form by the collapse of a magma chamber below a composite volcano during an explosive eruption
Define a Geyser
a geyser is a groundwater that boils in an underground chamber to periodically produce a release of steam or water
- (most famous geyser in the world is the old faithful)
What are Super Eruptions?
These are the products of supervolcanoes and are extremely rare events
What are Super Eruptions?
These are the products of supervolcanoes and are extremely rare events
- occur when a larg
What are Super Eruptions?
These are the products of supervolcanoes and are extremely rare events
- occur when a larg
How do super eruptions occur?
- 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.
Yellowstone National park sits on a massive caldera created from which volcano?
Yellowstone supervolcano
Where are most (if not all) volcanoes restricted to in canada
B.C or Southern Yukon
Which Mt provides the greatest actual risk to canada?
Mt. baker in Washington state
On average, How many volcanic eruptions occur each year?
50 to 60
Over the century, 400,000 people have been killed by eruptions. T OR F?
False, 100,000 people have been killed by eruptions over the century
What is a Caldera?
- A circular to an oval depression formed during the collapse of a volcano
- can be up to 25km in diameter
List effects of volcanoes
- powerful eruptions can impact global climate
- ash and gases reflect solar radiation causing a cooling
Define the term Lava Flows
- These occur when magma flows out of a central crater or a fissure on the side of a volcano
What are the two types of Lava
Pahoehoe Basaltic Lava
Aa basaltic lava
What is Pahoehoe basaltic lava
- low viscosity ( a few km per hour), high temperature. When hardened, it has a smooth texture
What is Aa Basaltic lava?
High viscosity (a few meters per day), lower temp. When hardened, it has a blocky texture
Define the term Lateral Blasts?
An eruption directed away from a volcano where materials are blown parallel to the surface
Define the term Pyroclastic flows?
These are avalanches of ash, gas, and rock fragments that travel down the slopes of a volcano during an explosive eruption =
What does the term Pyro mean? and what does the term Clatic mean?
Pyro means fire
clastic means broken in pieces
Most people have been killed by pyroclastic flows than any other volcanic phenomenon. T or F
True
Define the term Ash Fall?
Particles of ash can be carried downwind hundreds of kilometres from an eruption site
List the hazards of ash fall
- Destroys vegetation
- contaminates surface warer
- health hazards to people and animals
- causes aircraft engine failure
The type of smog that can induce asthma attacks and respiratory problems is referred to as
a vog
Explain the process of a sector collapse?
As magma travels up the channel, the volcano can inflate and its slopes can become over steepened, leading to a collapse in the flank of a volcano
Define the term Lahars?
Large amounts of material that become saturated with water and move downslope. It is an Indonesian word
What is another term of lahars
Mudflows
List some Natural Service Functions that are derived from volcanoes?
- Ancient volcanoes provided the gases that currently make up todays atmosphere
- Internal heat from volcanoes can produce renewable geothermal energy
- Volcanic soils are good for agriculture due to their porous, well drained, and nutritious feel
- volcanic landscapes attract tourism and recreation
- eruptions have created new land (Hawaii, Iceland)
What is an eruption forecast?
An eruption forecast is a statement of the probability that a volcano will erupt within a defined time
An eruption forecast is based on info provided by what?
- Monitoring seismic activity
- Thermal and hydrologic monitoring
- Land surface monitoring
- monitoring volcanic gas emissions
- understanding local geologic history
- Monitoring seismic activity
