volcanoes

Define tephra

any name for any vesculated thing that is ejected out of a volcano.

Geysers

caused into when surface water percolates down into the hot rocks that surround the magma chamber. The heated water now less dense rises toward the surface along faults and cracks

Volcanoes are dangerous when

feed viscous magma

Intermediate and felsic magma

have a higher silica content and are highly explosive = more violent

Mafic magma

have a low silica content 48%-50% and are less explosive = more gental

Mount St. Helens

is highly explosive it has a high gas and silica content with a low tempature

viscous magma

is like a thick cold molasses has a high viscosity produces a more violent eruption unlike a thin fluid water like magma that has a low viscosity

What comes out of volcanoes

no fire, just hot molten rock and gas.The molten rock becomes vescuticles as it is ejected, the general name for the particles is tephra

Concordant sill

runs parallel to the pre-existing bedrock. Laccoliths and sills are examples of concordant igneous rock bodies. A laccolith is a dome shaped intrusive body that has intruded between layers of sedimentary rock. The rising magma forces the overlying layers to rise up into a dome. A sill is similar to a dike with the exception that sills run parallel to the existing rock bed instead of cutting through it.

what makes magma viscous

temperature, gas content and silica content

Composite volcanoes

A tall steep sided symetrical cone-shaped volcano in which layers of rhyolite lava alternate with layers of ash. Rise to about 8000 feet above their base. Thick magma (viscous) rises to the surface through a conduit connecting the magma chamber to the surface. Also known as a stratovolcano.

Active volcanoes are located in

Hawaii, Cascade Range, the Aleutians, Yellow Stone, Long Valley, Valles Caldera, Long Valley (mammoth area) California

Three components of a geyser

Heat, hot rocks and water

Blocks and bombs

walnut to car size clasts of hardened lava

Nuee Ardentes

(Pyroclastic flows) Semi solid to solid fragments and hot expanding gases that flow down the flanks of a volcano. It moves much like a snow avalanche.

Intrusive igneous bodies

(plutons) Magma often cools beneath the ground to form plutons that have a variety of shapes and sizes. The shape of the pluton gives the name to the type of intrusion.

What percentage of earths surface is volcanic

80%

discordant dikes

A discordant igneous rock body cuts across the pre-exiting rock bed. Batholiths and dikes are examples of discordant rock bodies. A dike is a vertical or near vertical intrusive igneous rock body that cuts across rock beds. They frequently form from explosive eruptions that crack the area around a volcano with the magma filling the cracks forming a dike.

shield volcano

A low, flat, gently sloping volcano built from many flows of fluid, low-viscosity basaltic lava. It can be thousands of feet tall but not very steep. The thin flows erupt from the central summit, vents and flow down the sides in all directions

Lahar

An avalanche of volcanic water and mud down the slopes of a volcano. can reach speeds of 10-20 miles per hour

Sills

Another type of pluton that is formed when magma solidifies between two layers of rock.

Hot springs

Cooler emissions of water near extinct volcanoes. Temperature depends on rate of circulation of water through under ground channels and the amount of dilution by cool ground water. A pool formed by groundwater that has risen to the surface after being heated by a nearby body of magma.

Dikes

Formed when magma squeezes across rock layers and cools (vertically).

Plutons

Intrusive igneous rock bodies of any dimesion, including batholiths, stocks, sills, and dikes, formed through mountain-building processes and oceanic-oceanic collisions; can be exposed at Earth's surface due to uplift and erosion.

Volcanic necks

Is congealed magma within the throat of the volcano. The necks overlie the magma chamber. the neck is resistant to erosion and becomes exposed as the volcano erodes. It stands up in bold relief as column structures

Name 3 types of volcanic phenomena

Nuee Ardetes (pyroclastic flows), Lahars (volcanic mudflows) Calderas

Name of the geyser that erupts on a very regular schedule

Old faithful erupts every 65 minutes

Lapilli

Pea to walnuts size cinders

Silica content in magma

The higher the silica content the more viscous the magma is

lava dome

a bulbous mass made from highly viscous lava (low temp, high silica, low gas), which plugs the central conduit of volcanoes

Calderas

a huge bowl-shaped depression formed when an empty magma chamber collapses into the void after a volcanic eruption empties the magma chamber. 1-60 miles in diameter.

Caldera that re erupts is called

a resurgent caldera

Batholiths

are very large intrusions, many km's long and wide and very thick. Usually granitic due to slow underground cooling. Either a big pluton or a large body made up of smaller plutons

Why is a volcano more dangerous when the magma is viscous

because viscous magma requires great pressure to erupt, when it finally erupts it may be highly explosive

Lacolith

bulges rock layers above then cools before the magma can escape

Fumaroles

holes or cracks that serve as escape vents for underground gases like steam, hydrogen, sulfide and sulfuric acid. They are stinky but leave brilliantly colored stains on the surrounding rocks.

Ash is

mostly sand size glass shards, some broken crystals and rock fragments

Volcano gas is made up of

mostly water vapor, some sulfur and other oxides

Out-gassing over the last 4.5 billion years has formed

our atmosphere and the oceans

Tephra is named according to

particle size

Stocks

still a large pluton but much smaller than a batholith

Gas content in magma

the higher the gas content the more viscous the magma becomes

magma tempature

the hotter the magma the less viscous it is

Cinder cones

the simplest type of volcano, it is short lived. It is steep sided made of any composition like basalt, andesite and rhyolite. It is built of tephra (ash, lapilli, blocks and bombs) ejected from a single vent. It is usually only a few hundred feet high but rarely more than a thousand feet high, lava comes out of the bottom