Physical Geology Ch4

Volcanism

Any activity that includes the movement of magma toward or onto Earth's surface

Yellow Stone

Caldera. Huge. , Intraplate Igneous Activity: Continental.

Mount St helens

Catastrophically Erupting volcano, stratovolcano built up by molten rock, igneous, continental, mafic.

Temperature at which lavas solidify

Mafic ~1200*C, Felsic ~700*C

Krakatau

Volcano in Indonesia; erupted in 1893; lowered the global temperature by 5 degrees for a year

Dormant volcanoes

Volcanoes that have not erupted in thousands of years but are expected to in the future.

crater

a basin-like depression over a vent at a summit of the cone

Pyrocastic flow

a mixture of gas and pyroclastic debris that is so dense it hugs the ground as it rapidly flows to low areas.

What is the earliest sign of volcanic activity?

Seismic activity will increase to tell you that magma may be working its way to the surface.

What are 3 types of volcanos

Sheild, Cinder, and composite.

Spatter Cone

Vertical cones made of medium viscosity lava. The lava is "spit" vertically up. Lava is "belched out"

Lava Tube

conduits through which lava travels beneath the surface of a lava flow. Typically developed after most of a fluid, pahoehoe type lava has solidified. The tube provides insulation to the moving lava within the tube.

Volcanic rocks can only melt under what circumstances?

decompression melting and flux melting.

Pyroclastic Flow

fast moving flows of hot ash and pyroclastic debris

Volcanic hazard mitigation

three important concepts are hazard mapping, monitoring, and alerts.

What determines whether an eruption is explosive or quiet?

(1) The amount of gas dissolved in the lava or magma (2) the viscosity of the magma or lave; the more viscous the lava and the greater the volume of gases trying to escape the more violent the eruption. If the lava is less viscous (thinner) the gases can escape more easily, causing a quieter eruption.

Three Factors that influence the viscosity of lava

(1) The silica content. Mafic Lava (low in silica content) will flow more easily. Felsic, will flow more sluggishly.; (2) the temp of the lava, hotter=more fluid; (3) gases dissolved in lava, the greater the dissolved gas the more fluid. .

Pu'u 'o'o

250 meter high combined spatter and cinder cone on easter flank of kilauea sheild volcano. The exception to normal spatter cones that have very steep sides.

Pyrocrastic flows are accounted for ___ percent of volcano fatalities

30

Caldera

A large crater caused by the violent explosion of a volcano that collapses into a depression. Occurs when a volcanoes summit is blown off by expanding gases or when a volcano collapses into a partially emptied magma chamber.

Shield Volcano

A low, flat, gently sloping volcano built from many flows of fluid, low-viscosity basaltic lava

Kilauea

A non-explosive volcano that rests upon a mantle plume/ hot spot associated with intra-plate (why the islands keep moving). Kilauea is been active daily for nearly 30 year. Sheild volcano.

Volcanic activity at divergent boundaries

Decompression of the asthenosphere generates basaltic magma that contains only small amounts of water. Almost always consist of mafic lavas. Mostly effusive consisting of basaltic fluid magma and underwater, only sea level is in Sweden.

Explosive eruptions

Has magma high in silica (high viscosity, flows slowly), Magma builds up in the volcanoes pipe and gasses inside the magma build pressure and then expolde, incredible force of eruption;

Galeras

In 1992, nine people (six volcanologists and three tourists) were killed by a rain of blocks and bombs in a small eruption of a volcano in Colombia.

Volcano

Landforms formed by the extrusion of lava or ejection of rock fragments from a vent.

Volcanoes at Convergent boundaries

Most known and larger volcanoes occur at convergent boundaries where the oceanic lithosphere is being subducted into the mantle. . Most are composite volcanoes. Majority of lavas erupted along convergent margins are andesitic in composition. More viscous than basalt. Can evolve into an even more viscous lava causing rhyolite. Explosive eruptions due to viscosity and large amounts of water vapor.

Tephra

Pyroclastic material that can range in size from fine dust to ash. Dust is less than 1/8th of a millimeter. Ash is 1/8th to 2 millimeters. Cinder or lapilli is 2-64 millimeters, an blocks and bombs are larger than 64 millimeters.

Effusive eruption

a volcanic eruption characterized by low-viscosity basaltic magma and low-gas content, which readily escapes. lava pours forth onto the surface with relatively small explosions and few pyroclastics; tends to form shield volcanoes

Extinct Volcanoes

are those that have shown no activity in a long time and show no signs of ever erupting again.

Hawaii has mostly ___ lava

basaltic

Effusive eruptions are most commonly

basaltic in composition because mafic basalts are less viscous and gases can escape easily. Intermediate and felsic lava can erupt effusivley if the gas content is low.

Pillow structures

blobs of magma squeezed out of a thin skin of solid basalt and chilled into a pillow shape (or Pillow basalts). Fluid pahoehoe type lava.

Felsic Cinder cones

made up of fragments of pumice (also called pumice cones)

Vent

opening through which an eruption takes place

Why are Lavas rich in silica more viscous

silicate structures act like flour to water, the bonds thicken the lava.

Pahoehoe often changes into

'a'a flows as it gets further from the vent and cools to become more viscous.

'a'a

A slow flowing lava that, when hard, has a rough broken surface with sharp pierces of rock projecting from the flow. Shoved forward like a pike or rubble.

Cinder cone

A steep (33 degree slopes), smaller of the 3 types, cone-shaped hill or small mountain made of volcanic ash, cinders, and bombs piled up around a volcano's opening. Can have pyroclastic fragments of any composition but more commonly it is basaltic. Short lifespan. Vulnerable to erosion. Gas is depleted quickly.

When is a volcano considered active

if it is currently erupting or did recently

Composite Volcano

A tall, cone- shaped mountain in which layers of lava alternate with layers of pyroclastic fragments and lava flows. Mostly andesite. Also called a stratovolcano. Slopes less than 33 degrees. Intermittent eruptions, less vulnerable to erosion like cinder cones.

Columnar Jointing

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

pahoehoe

A type of lava that is very runny, billowy, ropey surface (like soup film). Formed by rapid cooling and solidification on the surface.

Geothermal Energy

Energy that comes from tapping natural underground reservoirs of steam and hot water produced by the earths natural internal heat engine

pyroclasts

Fragments blasted into the air during an explosive eruption where expanding, hot gases fragment rapidly, cooling magma into fragments and blasting them into the air.

Flank Eruption

Lava pours from a vent on the side of a volcano, unlike material being ejected from the central vent.

Flood Basalts

Lava that is very non viscous and flows almost as easily as water, does not build a cone around a vent, it just flows out of long fissures that extend through the earths crust. Lava basalts are vast outpourings of mafic lava from fissures that can cover wide areas with multiple flows that will build thick lava plateaus.

Within-plate activity

Occurs away from boundaries related to mantle plumes within plates. Mantle plumes are narrow upwellings of hot mantle material and partial melting occurs as a result of decompression. Large volumes of basaltic magma, generates large shield volcanoes. Can form caldera eruptions of rhyolite (yellow stone). Thought to be due to the melting of large amounts of thick continental crust by mafic mantle melts.

Circum-pacific belt

Ring of Fire. Major belt around the edge of the Pacific Ocean on which most composite volcanoes are located and where many earthquakes occur.

Lahars

Volcanic mudflows are responsible for 15% of volcano related fatalities. These are caused by huge amounts of loose pyroclastic material over slopes of the volcano and surrounding area that gets mixed with water or snow melt that forms a dense slurry of water, ash, and large boulders that will flow fast down the slope.

Mediterranean belt

a major concentration of earthquakes and composite volcanoes that runs through the Mediterranean Sea, crosses the Mideast and the Himalaya, and passes through the East Indies

MAfic magma is associated with more ____ eruptions

effusive

23% of volcano related death is caused by

famine that happens when there is wide spread destruction of the surrounding communities whether by climate issues or destruction.

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. High in silica, commonly solidify as obsidian. Often form within craters of composite volcanoes. Because it is too thick and pasty lava that is squeezed from the vent it is to viscous to flow and builds a steep sided dome or spine. Violent eruptions (like cork from wine)

Pyroclastic fall accounts for

the largest number of fatal events due to collapse of ash covered roofs or being hit by falling fragments.

Felsic magma is associate with the most ____ eruptions

violent; because they are the most viscous

Volcanic eruptions are accomapnied by the release of large amounts of gas such as

water vapor, carbon dioxide, and sulfur dioxide.