Chapter 6: Volcanoes & Other Igneous Activity

Pipe

A vertical conduit through which magmatic materials have passed.

Addition of Gases

H2O (from subduction zones), CO2 and SO2 (from ocean sediments sinking through.)

Volcano Forecasting

-Active: has a magma source; can erupt. -Dormant: not erupted in 10,000 years (Yellowstone) -Extinct: the source of magma is gone (Hawaiian Islands other than the Big One.)

Hazard Mitigation Measures

-Danger assessment maps -Evacuation -Lava flow diversion

Volcano Monitoring

-Geophysical methods: -Ground deformation: change in shape that can occur prior to, during or after an eruption -Remote sensing: any changes on the surfaces seen by GPS -Seismic monitoring: seismic stations monitoring EQs

Volcanic Hazards

-Lahars: an Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys. When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter. -Landslides -Earthquakes

Shield Volcano

A broad, gently sloping volcano built from fluid basaltic (mafic: high in Fe and Mg, low in Si) lavas. -Huge! Ex: Muana Loa, Hawaii

Rhyolitic Caldera

A cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption. Ex: Long Valley, California & Yellowstone

Vent

A conduit that connects a magma chamber to a volcanic crater.

Pyroclastic Flow

A fast-moving current of hot gas and rock. Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. They are a common and devastating result of certain explosive volcanic eruptions.

Columnar jointing of basalt

A geological structure where sets of intersecting closely spaced fractures, referred to as joints, result in the formation of a regular array of polygonal prisms, or columns. Columnar jointing occurs in many types of volcanic rocks and forms as the rock cools and contracts. Columnar jointing can occur in cooling lava flows and ashflow tuffs (ignimbrites), as well as in some shallow intrusions. Ex: Devil's Tower, Wyoming

Glowing Avalanche

A glowing avalanche is a gas rich suspension of one of the following - 1) Incandescent blocks, lapilli, ash and dust 2) Debris from a disintegrating lava dome or spine. 3) A pyroclastic flow which travells down depressions in the topography. A glowing avalanche is also called: fire avalanche, hot avalanche, volcanic avalanche.

Magma Chamber

A large underground pool of molten rock found beneath the surface of the Earth, which feeds a volcano.

Mid Oceanic/ Spreading Ridge

A mid-ocean ridge is an underwater mountain system that consists of various mountain ranges (chains), typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading center, which is responsible for seafloor spreading.

Cascade volcanoes

A number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 miles (1,100 km). The arc has formed due to subduction along the Cascadia subduction zone. Although taking its name from the Cascade Range, this term is a geologic grouping rather than a geographic one, and the Cascade Volcanoes extend north into the Coast Mountains, past the Fraser River which is the northward limit of the Cascade Range proper. Ex: Mt. Saint Helen's Shasta Mt. Lassen Mount Mazama/Crater Lake

Lava Fountains

A phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. Lava fountains may occur as a series of short pulses, or a continuous jet of lava. They are commonly associated with Hawaiian eruptions.

Composite Volcano

A volcano composed of both lava flows and pyroclastic material. Steep-sided, "layered cake" of explosively ejected materials: vicious sticky magma, gassy volatiles.

Alaskan Volcanoes

Alaska contains over 130 volcanoes and volcanic fields which have been active within the last two million years. Of these volcanoes, about 90 have been active within the last 10,000 years (and might be expected to erupt again), and more than 50 have been active within historical time (since about 1760, for Alaska). The volcanoes in Alaska make up well over three-quarters of U.S. volcanoes that have erupted in the last two hundred years.

Plinian eruption

Also known as Vesuvian eruptions, are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79. The eruption was described in a letter written by Pliny the Younger; it killed his uncle, Pliny the Elder.

Large Igneous Provinces

An extremely large accumulation of igneous rocks, including liquid rock (intrusive) or volcanic rock formations (extrusive), when hot magma extrudes from inside the Earth and flows out. The source of many or all LIPs is variously attributed to mantle plumes or to processes associated with plate tectonics.[1] Types of LIPs can include large volcanic provinces (LVP), created through flood basalt and large plutonic provinces (LPP).

Curtain Effusive

Basaltic magmas of low viscosity, low content of gases, and high temperature at the vent. Very little amounts of volcanic ash are produced. This type of eruption occurs most often at hotspot volcanoes such as Kīlauea and Iceland, though it can occur near subduction zones (e.g. Medicine Lake Volcano in California, United States) and rift zones. Associated with Hawaiian volcanoes.

Caldera

Collapsed volcano. Occurs after magma chamber empties. Ex: Crater Lake, Oregon

Monogenetic Fields

Collections of volcanic vents and flows, sometimes numbering in the hundreds or thousands typically from a single magma source.

Stratovolcanoes

Cone-shaped with steep slopes, explode frequently. Mount Vesuvius is best known for its eruption in AD 79 that led to the burying and destruction of the Roman cities of Pompeii and Herculaneum. That eruption ejected a cloud of stones, ash and fumes to a height of 33 km (20.5 mi), spewing molten rock and pulverized pumice at the rate of 1.5 million tons per second, ultimately releasing a hundred thousand times the thermal energy released by the Hiroshima bombing. Ex: Mount St. Helen's

Dike

Discordant igneous intrusions that cut across bedding surfaces or other structures in the country rock.

Volcanic Necks

Formed when magma in pipe solidifies without erupting. The rest of the volcano and surrounding sediments erode. This leaves "neck" exposed. Ex: Devil's Tower, Wyoming.

Lacoliths

Igneous intrusions that can lift the sedimentary strata they penetrate. -UFO shaped.

Pluton

Intrusive igneous structure. Blob-shaped magma chamber. They are structures that result from emplacement of magma into preexisting rocks.

Basalt Plateaus

Low viscosity (fluid) basalt la flows out of a fissure onto the surface, the basalt lava blankets a large area.

Gas Emissions

Magma contains dissolved gases that are released into the atmosphere during eruptions. Gases are also released from magma that either remains below ground (for example, as an intrusion) or is rising toward the surface. In such cases, gases may escape continuously into the atmosphere from the soil, volcanic vents, fumaroles, and hydrothermal systems. The most abundant gas typically released into the atmosphere from volcanic systems is water vapor (H2O), followed by carbon dioxide (CO2) and sulfur dioxide (SO2). Volcanoes also release smaller amounts of others gases, including hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL), hydrogen fluoride (HF), and helium (He).

Hawaii

Mauna Loa: largest volcano on Earth (shield) Mauna Kea: dormant shield volcano. Slope below sea level. Magma is more viscous generating steeper slope.

Decompression Melting

Melting, which is accompanied by an increase in volume, occurs at progressively higher temperatures with increased depth. This is the result of the steady increase in confining pressure exerted by the weight of overlying rocks. Conversely, reducing confining pressure lowers a rock's melting temperature. When confining pressure drops sufficiently, decompression melting is triggers. -Occurs where hot, solid mantle rock ascends in zones of convective upwelling, thereby moving into regions of lower pressure.

Sill

Nearly horizontal igneous intrusions that form when magma exploits weaknesses between sedimentary beds or other structures.

Pacific Ring of Fire

Ocean-girdling zone of crustal instability, volcanism, and earthquakes resulting from the tectonic activity along plate boundaries in the region.

Kimberlites

Oddball eruptions with deep magma sources (>200 km). Carbon exposed to huge pressure (makes diamonds). Ex: South Africa, Canada, Autralia

Lapilli

Pebble like bits of magma that cool in the air.

Intrusive Igneous Structures

Plutons, batholiths, lacoliths, sills, and dikes.

Bomb

Pyroclastic material. Comes out as melt and solidifies in air.

Nuee Ardentes

Pyroclastic material. Fast, hot ash/rock flows. Floats on cushion of hot gas/air and is almost frictionless.

Lahars

Pyroclastic material. Hot volcanic debris + water= mud flow. Follows stream valleys and gullies.

Cynders

Pyroclastic material. Small gravel.

Ash

Pyroclastic material. Small, dust sized. Ex: Ash falls in Vesuvius (79 ACE). Buried the city of Pompeii. Preserved human shapes and entire town.

Cinder Cones

Relatively small, cone-shaped, explosive volcanic features. In many ways, they resemble true volcano, but they lack significant internal layers of solidified lava required of true volcanoes. Scoria cones, also known as cinder cones, are the most common type of volcano. They are also the smallest type, with heights generally less than 300 meters. They can occur as discrete volcanoes on basaltic lava fields, or as parasitic cones generated by flank eruptions on shield volcanoes and stratovolcanoes.

Magma

Rock + heat. There are 3 main mechanisms to get it: decompression, heat transfer, and addition of gases. Associated with igneous rock. Occurs at subduction zones (convergent plate boundaries), where new crust is formed (divergent plate boundaries. i.e. mid-ocean ridges, continental rifts), and hot spots.

Pahoehoe Lava

Ropy, thin, twisted lava.

Common Types of Magama

Silica makes magma less flowy; gases make it more explosive. High viscosity = cold; not runny Low viscosity = hot; runny Basaltic: flows easily because of its low viscosity (A'a;Pahoehoe) Andesitic: Erupts explosively because of high gas content. Rhyolitic: Erupts catastrophically because of high gas content.

Crater

The depression at the summit of a volcano.

Batholiths

The largest intrusive igneous bodies. By definition, a plytonic body must have a surface exposure greater than 100 square kilometers in order to be considered a batholith. Anything smaller is called a stock. -Giant blobs.

Heat Transfer

Transfer of heat.

Pillow Basalts

Underwater "pillows" that form as lava crusts over.

Volcanoes

Vent or fissure in earth's crust from which molten rock reaches the surface.

A'A Lava

Vicious, jagged, blocky lava.

Fissure Volcanoes

Volcano that erupts mafic lava from linear pipes/vents and deposits sheet basalts. Fissures are usually found in or along rifts and rift zones, such as Iceland and the East African Rift. Fissure vents are often part of the structure of shield volcanoes. Ex: Columbia River Basalts

Extrusive Igneous Structures/Environments

Volcanoes: Composite, shield, fissure, volcanic necks, columnar joints, kimberlites, pyroclastic phenomenon.