A volcano is a place that allows hot material contained inside the earth to escape.
A caldera is a large volcanic depression formed by a collapse of the summit or flanks of a volcano.
Steps to a caldera
1. Volcanic eruption starts. 2. Continuing eruption destroys the previously constructed edifice. 3. The edifice collapses. 4. A newly created depression is filled with water.
Ejected volcanic materials
Hot rock (solid) : tephra
Hot rock (liquid) : lava
Four chemicals in magma
•oxygen (O)•silicon (Si)•aluminum (Al)•iron (Fe)
What is the most abundant gas in magmas?
Water vapor (steam)
Volcanic gases (Two)
CO2 and SO2
Rocks produced from volcanos
Setting of volcanos
Volcanoes form by the accumulation of erupted materials on the earth’s surface
The shape and size of the volcano depends on the type of material itself
duration and repetivity of eruptions
Two types of eruptions
Effusive - flows of molten rock
Explosive- ejecting molten and solid rock into air
Factors controlling volcanic activity
1. volcano plumbing- The presence or absence of pre-existing conduits for magma determines how fast a volcano that is ready to erupt will actually do so.
2. Magma viscosity-How readily magma can escape through the opening in the solid surface of a volcano,ability of liquids to resist flow
3. Gas pressure-The force that makes magma emerge from the volcano is the pressure of the gas dissolved in it. warms up it loses the ability to dissolve gas, and some gas escapes, forming bubbles. These bubbles take up more space then the same gas did when it was dissolved, and thus pressure inside a can rises. Escape of the gas from the liquid where it was dissolved is called exsolution (a process opposite to dissolution).
4. Freezing lava-Once the rock freezes, however, it becomes much harder for the gas to escape. Solid rock cannot yield to escaping bubbles of gas. If gas pressure is low, frozen rock will trap the gas inside. If the pressure is high, frozen rock will disintegrate in an explosive manner.
Types of volcanos
Monogenetic volcano-created by a single episode of eruption. It may last few hours or a few months, but as a rule once the eruption ends it is not repeated at the same place.
Stratovolcano- steep-sided, symmetrical cone-shaped mountains of large dimension, built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs. Their lower slopes are gentle, but they rise steeply near the summit. The summit area typically contains a small summit crater
Shield- broad, low-profile features (Hawaii's volcanos)
Caldera -a large volcanic depression formed by a collapse of the summit or flanks of a volcano. It can form in place of the stratovolcano or a shield volcano, and may involve the entire volcano or only a section of it.
Fissure-A fissure volcano is a linear opening (a crack, a gap) in the surface of the Earth through which volcanic products escape.
How do volcanos affect climate
1. Volcanic ash-particles block and diffuse sunlight, and as a consequence the lower part of the atmosphere becomes cooler.
2. Greenhouse gasses-The presence of certain volcanic gases in the atmosphere, most significantly water vapor and carbon dioxide, leads to the heating of the lower atmosphere through a “greenhouse” effect
3. Sulfer-emission of large quantities of SO2 into the atmosphere is the main reason volcanoes have a strong short-term impact on climate. After an eruption, SO2 interacts with water in the atmosphere to make tiny droplets of sulfuric acid, H2SO4. These droplets reflect back the sun’s rays, causing global cooling. The droplets linger in the air because their tiny size allows them to persist in the stratosphere for months to years
Types of volcanic hazards
1. Lava Flows- property damage
2. Ash falls- Larger lapilli and blocks fall near the source, smashing through roofs and cars. Finer ash accumulates farther from the source, blanketing the landscape and collapsing roofs. - air traffic
3. Pyroclastic flows- Travel down slopes extremely fast leaving no time for escape, hot and full of toxic gases, cuase death by burning and asphyxiaytion.
4. Blast- flatten anything in path if not straight up.
6. Lahars- (water + fresh volcanic ash) forms a raging torrent that can carry away houses, cars and architecture. Very dense
7. Tsunamis- if at or near sea level
8. Gas- suffication
Predicting volcanic eruptions including precursors
1. Attention to crater diameter which may be altered due to motion of magma-GPS
2. Measurements of the tilt of the volcano flank-shape of volcanos slopes is evidece that it is filling with magma-Carpenter's level
3. Satellite altimetry- time lapsed photos - satellites
Hawaii and volcanos
Mt St Helens
Landslides driving mechanisms
Optimal conditions for lanslides
Types and causes of masss wasting
Down slop emovement of rock and soil in response to gravity
Material may move by falling, sliding , spreading or flowing
Primary driving force is gravity acting on over-steepened slope
Other contributing factors:•Erosion by rivers and waves.•Saturation by snowmelt or heavy rains.•Earthquakes.•Volcanic eruptions.•Excess weight from human activities.