Chapter 6: Volcanoes and Other Igneous Activity

fissure

-A crack in rock along which there is a distinct separation

fumaroles

-A vent in a volcanic area from which fumes or gases escape.

vent

-The surface opening of a conduit or pipe.

Yellowstone-type calderas

- form from the collapse of a large area, caused by the discharge of colossal volumes of silica-rich pumice and ash along ring fractures

Hawaiian-type calderas

- form from the collapse of the top of a shield volcano caused by subterranean drainage from a central magma chamber

shield volcanoes

-A broad, gently sloping volcano built from fluid basaltic lavas. - most begin on the ocean floor as seamounts - ex. Hawaiian, Canary, Iceland, Galapagos, Easter islands, Nyamuragira volcano in Africa

hot spot

-A concentration of heat in the mantle capable of producing magma, which in turn extrudes onto Earth's surface. The intraplate volcanism that produced the Hawaiian islands is one example.

conduit

-A crack in rock along which there is a distinct separation

Crater Lake- type calderas

- the collapse of the summit of a large composite volcano following an explosive eruption of silica-rich pumice and ash fragments -these calderas eventually fill with rainwater, - ex. crate lake and wizard island

superplume

- very large mantle plumes -are though to be responsible for creating basaltic plateaus

pyroclastic flow

-A highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground. -a low-density cloud of hot expanding gases containing fine ash particles and a ground-hugging portion that is often composed of pumice and other vesicular pyroclastic material. - aska Nuee ardentes - usually the result of a collapse of an eruption column ex. Mount Pelee ans St. Pierre, and Vesuvius and Pompeii

calderas

-A large depression typically caused by collapse or ejection of the summit area of a volcano. -usually forms when the roof of solid rock above a magma chamber collapses. This usually occurs as the magma reservoir empties following a large eruption, or as magma migrates to the flank of a volcano to feed a fissure eruption

batholiths

-A large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and subsequently exposed by erosion. - generally felsic or intermediate

mantle plume

-A mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity. These are made of solid yet mobile material and may originate as deep as the core-mantle boundary.

columnar jointing

-A pattern of cracks that form during cooling of molten rock to generate columns that are generally six sided

stock

-A pluton similar to but smaller than a batholith - less than 100square km in area of surface exposure -many of part of would-be batholiths if fully exposed

welded tuff

-A pyroclastic rock composed of particles that have been fused together by the combination of heat still contained in the deposit after it has come to rest and by the weight of overlying material. tuff formed when the ash particles remained hot enough to fuse; consists mainly tiny glass shards

Cinder Cones (Scoria Cones)

-A rather small volcano built primarily of pyroclastics ejected from a single vent. Also known as a scoria cone.

intrusions/plutons

-A structure that results from the emplacement and crystallization of magma beneath the surface of Earth. Also known as an intrusion.

sill

-A tabular igneous body that was intruded parallel to the layering of preexisting rock. -concordant

dike

-A tabular-shaped intrusive igneous feature that cuts through the surrounding rock - discordant - tend to be more resistant to weathering than surrounding rock

concordant

-A term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock.

discordant

-A term used to describe plutons that cut across existing rock structures, such as bedding planes.

lava tubes

-A tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent. - allow fluid lavas to advance great distances.

Aa flows

-A type of basaltic lava flow that has a jagged, blocky surface. with sharp edges and spine projections

parasitic cones

-A volcanic cone that forms on the flank of a larger volcano.

Composite Cone (Stratovolcano)

-A volcano composed of both lava flows and pyroclastic material. Also known as a stratovolcano. -are large, nearly symmetrical structures consisting of alternating layers of explosively erupted cinders and ash interbedded with lava flows.

fissure eruption

-An eruption in which lava is extruded from narrow fractures or cracks in the crust. - responsible for the most of the volcanic material coming out from the crust

volcanic necks

-An isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano. Also known as a plug. - basically the remaining rock inside the volcanic conduit

pillow lava

-Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows

eruption columns

-Buoyant plumes of hot, ash-laden gases that can extend thousands of meters into the atmosphere.

flood basalts

-Flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters.

volatiles

-Gaseous components of magma dissolved in melt. - readily vaporize (form a gas) at surface pressures.

scoria

-Hardened lava that has retained the vesicles produced by escaping gases. - form from basaltic magmas have vesicular texture

decompression melting

-Melting that occurs as rock ascends due to a drop in confining pressure. ex. mid-ocean ridge - when pressure decreases, melting point of rock decreases

lahar

-Mudflows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels.

laccolith

-Relatively small, mushroom-shaped pluton that forms when magma intrudes into parallel rock layers close to Earth's surface. - arches the beds above while leaving the ones below relatively flat

basalt plateau

-The broad and extensive accumulation of usually basaltic lava from a succession of flows emanating from fissure eruptions ex. Colombian plateau and Deccan Traps

crater

-The depression at the summit of a volcano, or that which is produced by a meteorite impact

geothermal gradient

-The gradual increase in temperature with depth in the crust. The average is 30°C per kilometer in the upper crust

partial melting

-The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.

pyroclastic material (tephra)

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

Ring of Fire

-The zone of active volcanoes surrounding the Pacific Ocean.

pumice

-a very light and porous volcanic rock formed when a gas-rich froth of glassy lava solidifies rapidly. - forms from andesitic or rhyolitic magmas - are usually lighter in color and less dense than scoria

volcanic cone

-e A cone-shaped structure built by successive eruptions of lava and/or pyroclastic materials.

Pu'u O'o Crater

-is a volcanic cone in the eastern rift zone of the Kīlauea volcano of the Hawaiian Islands. Until the end of April 2018, Puʻu ʻŌʻō had been erupting nearly continuously since January 3, 1983, making it the longest-lived rift-zone eruption of the last two centuries

volcanic bombs

A projectile of hot magma or rock that is blown from the vent during a volcanic eruption. These solidify in flight and frequently form an elongated rock of streamlined shape. - more than 64mm

effusive eruptions

A quiescent eruption that produces mainly outpourings of fluid lava

dike swarms

Flows sources identified as multiple aligned dikes

-The flanks of Mauna Loa have gentle slopes of only a few degrees. This low angle results because very hot, fluid lava travelled "fast and far" from the vent. In addition, most of the lava (perhaps 80 percent) flowed through a well-developed system of lava tubes. Another feature common to many active shield volcanoes is a large, steep-walled caldera that occupies the summit -In the final stage of growth, shield volcanoes erupt more sporadically, and pyroclastic ejections are more common. Further, lavas increase in viscosity, resulting in thicker, shorter flows. These eruptions tend to steepen the slope of the summit area, which often becomes capped with clusters of cinder cones

How do shield volcanoes form?

-Cooling that occurs as the flow moves away from the vent is one factor that facilitates the change from pahoehoe to aa. -The reduction in temperature increases viscosity and promotes bubble formation. -Escaping gas bubbles produce numerous voids (vesicles) and sharp spines in the surface of the congealing lava. -As the molten interior advances, the outer crust is broken, transforming a relatively smooth surface of a pahoehoe flow into an aa flow made up of an advancing mass of rough, sharp, broken lava blocks

How does pahoehoe lava turn into aa lava?

- basaltic (mafic) magmas have a low-silica content, and the lowest gas content, and erupt at high temp - rhyolitic (felsic) magma have a high-silica content and high gas content, and erupt at lowest temperatures - andesitic lavas are somewhere in between the above two.

How does silica and gas content vary with different rocks?

- The vast majority of lava on Earth—more than 90 percent of the total volume—is estimated to be basaltic in composition. Andesites and other lavas of intermediate composition -account for most of the rest, while rhyolitic (felsic) flows make up as little as 1 percent of the total.

The vast majority of Earth's lava is of what composition

silica content: The more silica in magma, the greater its viscosity. Silica impedes the flow of magma because silicate structures start to link together into long chains early in the crystallization process. - rhyolitic magma is super viscous temperature: the hotter the magma the less viscous it is

What 2 factors affect viscosity?

Aa Flows and Pahoehoe Flows

What 2 types of lava flows do basaltic magmas produce?

-(1) in zones of upwelling, a decrease in pressure (without an increase in temperature) can result in decompression melting; (2) the introduction of water can lower the melting temperature of hot mantle rock sufficiently to generate magma; and (3) crustal rocks can be heated above their melting temperature by hot mantle-derived basaltic magma or during continental collisions

What are 3 ways magma can be generated?

- basaltic compositions -Because cinder cones are composed of loose fragments rather than solid rock, the lava usually flows out from the unconsolidated base of the cone rather than from the crater. -have a high angle of repose (the steepest angle at which material remains stable) and are therefore steep-sided, with slopes between 30 and 40 degrees. -In addition, cinder cones have quite large, deep craters in relation to the overall size of the structure. -Although relatively symmetrical, some cinder cones are elongated and higher on the side that was downwind during the final eruptive phase -Most cinder cones are produced by a single, short-lived eruptive event

What are some characteristics of cinder cones?

-In general, composite cones are the product of silica-rich magma having an andesitic composition. -However, many composite cones also emit various amounts of fluid basaltic lava and, occasionally, pyroclastic material having felsic (rhyolitic) composition. 0The silica-rich magmas typical of composite cones generate thick, viscous lavas that travel less than a few kilometers. -In addition, composite cones are noted for generating explosive eruptions that eject huge quantities of pyroclastic material -Coarse fragments ejected from the summit crater tend to accumulate near their source and contribute to the steep slopes of the summit area. Finer ejected materials, on the other hand, are deposited as a thin layer over a large area that acts to flatten the flank of the cone.

What are some characteristics of composite volcanoes

-include large outpourings of fluid basaltic lavas like those that compose the Columbia River basalts, the Siberian Traps in Russia, India's Deccan Plateau, and several large oceanic plateaus, including the Ontong Java Plateau located in the western Pacific ex. Hawaii as well

What are some examples of intraplate volcanism

- volcanic island arcs, continental arc

What are some examples of volcanism at convergent boundaries?

- pillow lava at mid-ocean ridge - fluid basalt outspourings at east african rift

What are some examples of volcanism at divergent boundaries

water vapor and carbon dioxide - followed by SO2, H2S, CO, N2

What are the 2 most abundant gases in magma?

Volcanoes built primarily of pyroclastic materials typically have craters that form by gradual accumulation of volcanic debris on the surrounding rim. Other craters form during explosive eruptions as the rapidly ejected particles erode the crater walls. Craters also form when the summit area of a volcano collapses following an eruption.

What are the different ways a crate can form?

shield volcanoes, cinder cones, and composite volcanoes

What are the three major types of volcanic cones

Crater Lake- type calderas, Hawaiian-type calderas, Yellowstone-type calderas

What are the three types of calderas

Mauna Loa

What is Earth's largest shield volcano

Kilauea

What is Hawaii's most active volcano?

Basaltic flows because they have less gas content and are less viscous. - pressure does not build up to extreme levels which can cause an eruption

What type of lava is associated with effusive eruptions and why?

rhyolitic magma because it has a high gas content and high viscosity which traps gas and builds confining pressure - this results in an explosion

What type of lava is associated with explosive eruption

-, because sills generally form in near-surface environments and may be only a few meters thick, the emplaced magma often cools quickly enough to generate a fine-grained texture.

Why are dikes and sills usually fine-grained?

- magmas generated by mantle tend to be basaltic - these basaltic magmas are less dense than surrounding rock near oceanic crust so basaltic flows develop - on continental crust however, the basaltic magma is more dense than continental crust, but it is still hot enough to melt the above rock - this results in silica-rich lava flows from melted continental rock

Why is there more often basaltic lava flows in the ocean and rhyolitic lava flows on continents

pahoehoe flow

a lava flow with a smooth-to-ropy surface - is hotter and more fluid that aa flows - can transform into aa lava but the reverse can not happen

viscosity

a liquid's resistance to flow

tabular

describing a feature such as an igneous pluton that has two dimensions that are much longer than the third - table like

lapilli

pebble like bits of magma that cool in the air between 2mm-64mm

host rock (country rock)

preexisting crustal rocks intruded by magma. -may be displaced or assimilated by magma

massive

refers to an igneous pluton that is blob-shaped - not tabular

volcanic block

the largest pieces of pyroclastic material, are pieces of solid rock erupted from a volcano

submarine volcanism

the process by which basaltic lavas erupt on the seafloor

volcanic ash

tiny particles of pulverized volcanic rock and glass - less than 2mm