Volcanoes

Location of active and recently active volcanoes in the US

What is a Volcano? (1) A vent from which melt from inside the Earth spews out onto the planet’s surface; (2) a mountain formed by the accumulation of extrusive volcanic rock. SO, it does not have to be a mountain, it can also be a vent, or a caldera

Vent eruptions. These are common, and are mostly found along the ocean floor at mid-ocean ridges; but they also occur on land.

More tradition type of eruption

Vent eruption

Vent eruption

Don’t forget that midocean ridges are vent eruptions!

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Calderas usually form after large eruptions. The magma chamber below empties, and the roof collapse down into the emptied chamber.

Yellowstone national park is located over a very large caldera. This is how all of the geothermal activity is generated. This caldera has erupted in the past, and may erupt again

What ‘spews’ out of a volcano? Lava, gas, ash and larger size particles. The lava consists of magma (molten rock). the composition of the magma depends on the tectonic setting of the volcano. Compositions can range from basaltic (mafic) to rhyolite (felsic), can be made of carbonate (rare), or can be made of feldspathoids (also rare). Why do volcanoes erupt? Because of dissolved gasses in the magma. Just like a bottle of soda a liquid can have dissolved gas init. When the pressure of the dissolved gas become too great, the gas wants to escape.

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The greater the amount of volatiles (such as water) the more violent the volcanic eruption.

Basalt has the highest temperature of any lava, typically between about 11701100°C (~2140-2000°F). The other lava types (andesite, dacite, and rhyolite) form cooler flows with temperatures between about 1000-800°C (~1800-1500°F); some flows can still move slowly at temperatures as low as about 600°C (~1100°F).

This picture shows that the introduction of water can make a volcanic eruption more violent.

Defined: A subaerial volcano with a broad, gentle dome, formed either from low-viscosity basaltic lava or from large pyroclastic sheets.

Hawaii is an example of basaltic volcanism by a hot spot ( a plume of material thought to have originated from within the earths mantle).

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lava flow: Sheets or mounds of lava that flow onto the ground surface or sea floor in molten form and then solidify.

These are 3D drawings of lava flows. the top flow is an a’a’ flow (A lava flow with a rubbly surface.), while the bottom flow is a pahoehoe flow (A lava flow with a surface texture of smooth, glassy, rope-like ridges.) in a lava tube.

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Here is a 2D view of a lava tube (The empty space left when a lava tunnel drains; this happens when the surface of a lava flow solidifies while the inner part of the flow continues to stream downslope.).

Here is your teacher in a lava tube in northern AZ.

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When basaltic lava cools is forms columnar joints (A type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flow cools.)

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Top view of columnar joints

Flood basalt: vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and lava is particularly hot and has low viscosity. These are also basaltic in composition.

Cinder cone: A subaerial volcano consisting of a cone-shaped pile of tephra whose slope approaches the angle of repose for tephra.

SP crater is an example of a cinder cone that has a lava flow emanating from its base.

Here is an example of cinders from a volcanic eruption.

A large, cone-shaped subaerial volcano consisting of alternating layers of lava and tephra.

Mt St Helens is a composite cone. It eruption in 1980 was very violent, and even though we knew it was going to happen, people still died.

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A stratovolcano such as Japan's Mount Fuji consists of alternating layers of ash and lava. This animation examines the processes by which a stratovolcano forms.

8PC version

The different types of volcanoes occur in different sizes.

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Where do the volatiles come from to make composite cone eruptions so violent? From the dehydration of a subducting slab.

The most abundant gas typically released into the atmosphere from volcanic systems is water vapor (H20), followed by carbon dioxide (C02) and sulfur dioxide (S02). Volcanoes also release smaller amounts of others gases, including hydrogen sulfide (H 2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL), hydrogen fluoride (HF), and helium (He).

The volcanic gases that pose the greatest potential hazard are sulfur dioxide, carbon dioxide, and hydrogen fluoride. Sulfur dioxide irritates skin and the tissues and mucous membranes of the eyes, nose, and throat. Hydrogen sulfide at low concentrations it can irritate the eyes and acts as a depressant; at high concentrations it can cause irritation of the upper respiratory tract and, during long exposure, pulmonary edema (fluid in the lungs). Carbon dioxide is dangerous in large volumes. Breathing air with more than 30% CO 2 can quickly induce unconsciousness and cause death

It is thought that most of the Earth’s water originated from volcanic eruptions.

Gasses emitted from volcanic eruptions are sometimes called VOG.

Gasses erupted from volcanoes can also be converted when in the atmosphere to other chemical compounds.

These trees were killed by high amounts of CO2 in the soil. (Long Valley, CA)

Vapor, created as the lava enters the ocean water, is called laze. It is rich in acids (such as HCl) and the rain water it creates is extremely acidic (1.5-2.5 pH)

Suspended particles, such as dust and ash, can block out the earth's sunlight, thus reducing solar radiation and lowering mean global temperatures. This is called the haze effect. The 1980 eruption of Mt St Helens lowered global temperatures by 0.1 C, while other, larger eruptions, such as Laki (1783) lowered temperatures by ~5 C. This all depends on the amount of S-rich gasses the eruption emits. Sulfur combines with water vapor in the stratosphere to form dense clouds of tiny sulfuric acid droplets. These droplets take several years to settle out and they are capable to decreasing the troposphere temperatures because they absorb solar radiation and scatter it back to space.

Pyroclastic flow (nuee ardente): fastmoving avalanche formed when hot volcanic ash and debris mix with air and flows down the side of a volcano. It is usually constricted to valleys. Ash: Tiny glass shards formed when a fine spray of exploded lava freezes instantly upon contact with the atmosphere. Lapilli: Marble-to-plum-sized fragments of pyroclastic debris. Tephra: general term for fragments of volcanic rock and lava regardless of size that are blasted into the air by explosions or carried upward by hot gases in eruption columns or lava fountains

Pyroclastic flow

When a volcano erupts, a large amount of the material falls back down to earth. This is because it is ejected from the volcano at a high velocity, but gravity soon takes over, and it falls back to earth as ash falls, volcanic bombs, or pyroclastic flows. A large volume of ash though, can reach great height (known to go as high as the troposphere), and is carried aloft by winds.

Pyroclastic flow contains fragments ranging in size from ash to boulders traveling greater than 50 miles per hour, and can reach temperatures between 200°C and 700°C. They destroy by: 1)direct impact, 2)burying, 3)melting snow and ice to trigger lahars, and 4)burning.

Volcanic bombs: are lava fragments that were ejected while viscous (partially molten) and larger than 64 mm in diameter. Many acquire rounded aerodynamic shapes during their travel through the air.

Ash can: 1) turn daylight into darkness, 2)colapse roofs, 3)abrade machinery and vehicles, 4)cover farmland, 5)cause roads to be slippery or blocked, 6)cause municipalities to close (such as power and water), and 7) can cause suffocation or silicosis (a type of lung cancer).

Many routes that planes follow fly over active volcanoes. This is an example of air traffic that flies over active volcanoes of the Pacific ring of fire.

Once ash is aloft in the atmosphere, it becomes a hazard to air traffic

This diagram displays what happens when ash enters jet engines.

Lahar: A thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano. Can form when volcano erupts, melting snow and ice on its summit, when heavy rains fall after a volcanic eruption, or my a landslide.

Lahars can: 1) destroy by direct contact 2) lead to increased deposition in streams (alter base level) 3)block tributary streams 4)bury valleys and communities with debris

Volcanic-danger assessment maps are one way to mitigate volcanic hazards. It is important to inform the public that live in a possibly hazardous volcanic zone.

Volcanic eruptions are also associated with, or can cause, landslides and earthquakes.

These are locations of epicenters form earthquakes from the fall 2004 eruption of Mt St Helens. During the 1980 eruption, magnitudes reached as high as 5.0

A landslide triggered the 1980 eruption of Mt St Helens by exposing its magma chamber releasing its dissolved gasses.

Possible ways to “predict” a volcanic eruption: 1) Numerous earthquakes will occur usually before a volcanic eruption. 2) Usually a “bulge” will form. 3) the ground surface will heat up. 4) Smoke comes out of it.