Volcanoes and Related Hazards

Volcanic mudflows

(debris flow or lahars) are "rivers" of ash and water that flow 20-40 mph with the consistency of wet concrete and destroy everything in their paths. Dense and viscous

What are the 5 predictive tools used to monitor and detect volcanic activity?

1) geologic history - look at how a volcano has behaved in the past (looking at volcanic deposits-size shape, composition, layer etc) 2) topographic changes - looking at the change in the shape of the volcano (when magma chamber forms parts of the volcano will swell and deflate) 3) seismic monitoring - small earthquakes are created as the swelling and straining of rocks takes place; they occur in swarms 4) monitoring volcanic gases - scientists look for changes in the gases begin released and for where the gases are coming from (they do a chemical analysis of samples; if lots of CO2, SO2 and water vapor, then it's from magma) 5) Geophysical & Groundwater Changes - changes in the rocks and in the water; rock temps and water temps increasing, water acidity and sulfur content increasing; electrical resistance of rocks often changes

environmental hazards associated eith volcanic ash

1) inhaling the particles (very dangerous for children or adults with cardiac or repiratory conditions) 2) when it falls from the sky and forms a blanketlike deposit on the landscape (destroys crops & causes buildings to collapse, disrupts pollination and changes the soil acidity, contaiminates water, causes flooding when ash washes off into rivers, ruins electrical machinery by causing shorts)

Why are pyroclastic flows so dangerous?

1) the weight of the rocks involved and the fact that the material can travel on average of around 50 mph but can read upwards of 450 mph 2)the high temp of the gases inside the flow which ranges between 400-1,500 degrees

When do pyroclastic flows form?

1) when a rising eruption column begins to callapse on itself, sending hot gases and fragmental material down the flanks of the volcano 2) during explosive blasts when hot fragmental material is sent rushing along the ground surface away from the volcano 3) when gases escape rapidly from erupting lava, creating a frothing mass of semimolten material that rolls downslope 4) in noneplosive eruptions when a growing lava dome becomes unstable due to the oversteepening of its slopes which leads to partial or total collapse of the dome, sending large volumes of hot rock tumbling down the volcano

How do volcanic mudflows typically form?

1) when loose ash lying on the flanks of composite cones is picked up my moving water from either rain events or by rapidly melting snow and glacial ice 2) sudden slope failure near volcano's ice-capped summit results in a massive landslide of raock and ice; as debris travel downslope, some of the ice wil begin to melt, transforming the landslide into a mudflow

viscosity

A liquid's resistance to flow (more silica means greater resistance or less ability to flow).

Describe how gas a water create more explosive volcanoes.

Along subduction zones where water-rich sediment is mixed into the melt, large volumes of H2O gas are generated making andesitic magmas highly explosive

Which is more likely to experience volcanic landslides due to its steeper slopes, shield volcanoes or composite cones?

Composite cones

volcanic ash

Fine particles of mineral matter from a volcanic eruption which can be dispersed long distances by winds aloft

How does temperature affect viscosity?

Higher temperatures mean less viscosity (faster flow); lower temps mean greater viscosity (slower flow)

What will the mudflow detection system that has been installed near Mt. Rainier do?

It is a network of seismic sensors at 5 stations located in the upper reaches of the two most vulnerable vallesy in the area. It detects seismic waves that are generated by modflows. If the waves reach a specific limit, it will trigger a radio signal to an emergency management ops center.

lava flows

Moving masses of molten lava, or sheets of rock formed when lava solidifies

How well prepared is the world for earthquakes?

Only a small number of the world's volcanoes that threaten populated areas are well monitored and have instruments with real-time data transmission capabilities. Most volcanoes are only lightly monitored. Some dangerous volcanoes are not being monitored at all. Also, if an eruption is forcasted and the information isn't reliable, then the next time, people are less likely to evacuate (not taking it seriously)

Where is a very good example in the United States of an area in serious risk of a mudflow?

Seattle Tacoma metropolitan area (in the shadow of Mt. Rainier)

magma chamber

The pocket beneath a volcano where magma collects.

pyroclastic material

The volcanic rock ejected during an eruption, including ash, bombs, and blocks

Where do volcanic gases originate from?

When rocks begin to melt deep within the Earth, they dissolve and produce volcanic gases that remain dissolved in the newly formed magma.

andesitic magma

When rocks go through partial melting the magma tends to be this as it contains less iron and magnesium but more silica

hot spots

a break in the crust where magma has been pushing up and as the plate moves the magma is stationary creating new volcanoes

crater

a circular depression formed around the vent of a volcanoe where material is being ejected into the air

scarps

a clifflike face which are characteristic of landslides (many found in the Hawaiian Islands)

magma

a molten mixture of rock-forming substances, gases, and water from the mantle (lithosphere)

Composite Cone

also known as a stratovolcano; cone-shaped features with steep slopes consisting of alternating layers of pyroclastic material and lava flows; usually associated with viscous and gas-charged adesitic magmas that generally erupt in an extremely explosive and violent manner; usually found along subduction zones (example is the Andes Mountains and Mount Fuji)

What are the three classes of magma?

basaltic, andesitic and rhyolitic

Why is a volcanic gas cloud so hazardous to humans?

because it contains no free oxygen (those who breathe it suffocate--asphyxiation) also when breathed in, the heat can damage the lungs

What causes an eruption to be more explosive?

bubbles from the gasses in the magma form and escape into atmosphere--if there's a lot of dissolved gas, the gas in the magma will decompress in an explosive manner

caldera

circular depression that forms AFTER the eruption when rocks in the subsurface begin to collapse or subside; forms when large volumes of magma are ejected from a shallow magma chamber leaving it relatively empty. The roof of the chamber then becomes unsupported and weak causing it to collapse

What type of volcanoe produces the most explosive and dangerous blasts?

composite cone volcanoes (stratovolcanoes)

vocanic ash

consists of jagged rock and glass fragments less than 2 millimeters in diameter that is carried by hot expanding gasses into the atmosphere and transported around the globe; extremely abrasive and fairly dense

basaltic magma

contains the most iron and magnesium and generated in the upper mantle from ferromagnesian rich rocks that contain very little water

pyroclastic flow

dry avalanche consisting of hot rock fragments, ash and superheated gas all rushing down the side of a volcano at great speed (almost always associated with more viscous silicon rich magmas)

Shield Volcanoes

exceptionally large landforms made up of mostly basaltic lava flows which flow very slowly. This means the laval flows can travel great distances from the vent and spread out over large areas.

lava domes

formed when highly viscous lava is extruded from a vent and forms a rounded, steep-sided dome. The lava piles up around and on the vent instead of flowing away, mostly growing by expansion from within. Lava domes commonly occur within the craters or on the flanks of composite volcanoes.

Rhyolitic magma

formed when the basaltic magma rises through the continental plates which is composed of granitic minerals with even higher proportions of silica which leads to this type of magma.

What plays a greater role in the transporting of volcanic debris, gravity or gases?

gases

What often triggers volcanic landslides in addition to volcanic eruptions?

heavy rains or earthquakes. A key factor is the movement of corrosive gases and groundwater within a volcano that breaks down feldspar-rich rocks into much weaker clay minerals. This weakens the rocks that make up the volcano and destabilizes the slopes making it easier for an earthquake or heavy rain to trigger a landslide.

continental flood basalts

huge flows of basaltic lavas that are erupted along fractures in the earth's crust

tsunamis

in addition to forming from an eathquake event, a volcanic tsunami can form when a volcano explodes violently in an oceanic setting. They also form from volcanic landslides.

lava

magma that reaches the Earth's surface

cause of volcanic eruptions

molten rock gathers in magma chamber. The weight of the overlying rock creates overburden pressure, which is offset by the magma's fluid pressure. As magma rises and encounters less overburden, the fluid pressure is able to open fractures, creating possible pathways to the surface. At the surface the pressurized magma is allowed to expand freely

Where do we find extremely explosive volcanoes?

near subduction zones (lots of andesitic magma which has lots of dissolved gas) & in the interior of continental plates (rhyolitic magma which has a lot of water)

What increases the risks of volcanic hazards to humans?

people chosing to live in hazardous zones for the better resources, complacency (because of time interval between eruptions, they consider the risk of an eruption low), growing population that is settling in high risk areas

Problems/hazards of lava flows

push, bury or burn people and things/property

What hazards are associated with volcanoes?

push, bury or burn people and things/property; additionally, mudflows, landslides, deadly gases

What is the most common hazard from explosive volcanoe blasts?

pyroclastic material and hot gasses that get blasted away from the volcano (pyroclastic material carries pulverized bits of rock along with superheated gases and blobs of lava creating a cloud that obliterates and burns up everything in its path)

Cinder cones

relatively small features that form when lava is ejected into the air and cools into pyroclastic material called cinders, which then fall and accumulate around the vent.

mass wasting

the transfer of rock and soil downslope under the influence of gravity

What is the best approach for noneruptive hazards?

to install sensors to detect the movement of earth materials as they begin to move downslope. Once a slide or flow is detected, a signal is sent to an early warning system that automatically alerts residents farther down the drainage system so they can quickly move to higher ground.

Things that have been tried to minimize damage/hazards of lava flows

using explosives as a way to disrupt moving lava so that a new direcion of flow is created, placing an earthen barrier in the path of an advancing flow to divert it away from human structures, spraying large volumes of water on the leading edges of a lava flow creating a chilled zone and a more continuous barrier made of rock.

When the steep flanks of a volcano become unstable and the underlying material fails, this results in rocks, snow and ice moving rapidly downslope in what is known as a ____________ ___________________.

volcanic landslide (debris avalanche)

What makes up 95% of all volcanic gases?

water vapor, carbon dioxide, and sulfur dioxide

What can societies do to minimize the risks of living in volcanic hazard zones?

we have limited succes in diverting lava flows; the only thing we can do is to simply get out of the way! We can take advantage of reliable warning signs of eruptions such as swarms of earthquakes, topographic bulges, escaping gases that scientists monitor.