Nat disasters 5-8

The magmas associated with the most violent and explosive volcanic eruptions are ______ magmas.

andesitic

basaltic

rhyolitic

rhyolitic (b/c they are viscous & contain a fair amount of dissolved water

This type of melting occurs when mantle rocks rise upward and experience lower pressure: \_______________

decompression

Viscosity :

Controls whether magma flows away or piles up

Volatiles :

Controls the explosivity of an eruption

Volume :

Controls the intensity of an eruption

A relatively small volcano constructed of pyroclastic debris piled up around a central vent is called a(n) :

cinder (scoria) cone

Which of the following best describes a stratovolcano?

* a large volcano composed of alternating layers of pyroclastic fragments and solidified lava flows
* a broad, gently sloping volcano constructed of solidified lava flows
* a steep-sided, dome-shaped mass of solidified viscous lava
* a volcano constructed of pyroclastic fragments ejected from a central vent
* a large volcano composed of alternating layers of pyroclastic fragments and solidified lava flows

Viscosity -

The property of a material that offers internal resistance to flow, its internal friction. The lower the viscosity, the more fluid the behavior.

Volatiles -

Describes substances that readily become gases when pressure is decreased or temperature increased.

water has \_____ viscosity

low

honey has \_____ viscosity

high

Viscosity depends on three things-

composition, temperature, and crystals

Pressure in magma comes from \_______, or dissolved gases.

volatiles

what are volatiles

dissolved gases

three types of magma:

basaltic, andesitic, and granitic

\________ magmas have the least silica (silicon dioxide), the highest temperatures, so have the lowest viscosity

Basaltic

\_________ magmas have the highest silica and lowest temperatures, so have the highest viscosity, meaning gases struggle to move through the fluid, build up more and more pressure and produce violent eruptions

Granitic

\_________ magmas are half-way between the other two in composition, temperature, and viscosity, but tend to erupt more like granitic volcanoes.

Andesitic

Obsidian -

Dark volcanic glass

Pumice -

Volcanic glass so full of gas bubbles that it commonly floats on water

Scoria -

Basaltic rocks with numerous air bubbles formed by gases excaping from magma

Pompeii is a city in Italy that was destroyed by Mt. Vesuvius. Pompeii saw ash fall and pumice rain, but the real killer was the \____________ \________, a ground-hugging cloud of ash, rock, lava, and scorching hot gases that came roaring down the mountain at 120 km/h.

pyroclastic flow

What is a pyroclastic flow?

a ground-hugging cloud of ash, rock, lava, and scorching hot gases that come roaring down the mountain quickly (at 120 km/h)

what is a stratovolcano made of?

layers of loose pyroclastic material and layers of lava

What is a lahar?

a silent killer that a lot of people, even those in danger zones, have never heard of. During an eruption, the steam that was in the magma rises with the ash, condenses and can rain back down onto the volcano, turning the loose material into mud, which flows downhill. Mud is much more ==powerful== than water, so it can travel farther, pick up rocks and trees along the way, destroying everything in its path.

second deadliest volcanic disaster in the 20th century happened because of a \________ when a volcano in Columbia named Nevada del Ruiz erupted late one night.

Lahar

what happened?

eruption and thunderstorm occured, weren't alarmed because they couldn't hear it, thick glacier on the summit was melted, turned the pyroclastic material to mud and lahars charged down the mountain

What is a caldera?

a massive depression that forms after a humongous eruption occurs because before the eruption, the ground was supported by magma (caramel) and after, it is hollow, so it collapses.

thrust faults

are just like reverse faults, where the hanging wall moves up relative to the footwall, but in a thrust fault, the fault plane is at a very low angle, often around 25 degrees often found in mountain building events and are usually near the edges of deformation (just like reverse faults)

Subduction zones are often classified as \________ faults.

thrust

We can predict the likelihood of a specific size earthquake on a specific portion of a fault within a \______ year span

10/50/100

we'd love to know when an earthquake was going to occur, but can we?

no, The problem is that all the energy that drives earthquakes, and the friction that locks up faults, all occurs deep underground. There is no way for us to "see" a fault plane in its entirety, and there is no way for us to measure the amount of stress building up in any location on a fault. It's a daunting task, and scientists are constantly looking for new ways to measure all the variables at work.

not all earthquakes are natural. humans do things to the earth every day that cause energy build up, or even fractures and faults to form. like what?

process of oil exploration called hydraulic fracturing, or fracking or by building dams

Currently, the most seismically active area of North America is \__________

Oklahoma