Chapter 11: Volcanoes, Deformation, & Earthquakes

What is a Fold and what are the main types of Folds?

-most rock layers are horizontal Compression: causes shortening often accomodated by folding of the layers. (creases) ***can form folds, reverse faults, or both ***most common along convergent plate-tectonic boundaries

What stresses form joints?

-mostly due to burial and to tectonic forces: may push, pull, or shear the rock. - cut by vertical joints formed by tectonic stresses -stress builds up as rock get warmer or cooler. (columnar joints- commonly meet at 120 degree angles) -stresses also arise during uplift of buried rocks, causing rocks to fracture due to reduced pressure. These joints are called "unloading points": form parallel to the surface and slice off thin sheets of rock.

Why is the Yellowstone Caldera considered to be dangerous?

-one of the world's largest active volcanic areas, occurring directly over a continental hotspot.

What are the hazards associated with Pyroclastic eruptions?

-race downhill and across the landscape at hundreds of km per hour: -incinerating and smothering any creature in its path. -burying and killing dozens of people. -huge column of volcanic ash that rose 15 miles into the atmosphere.

What is the Composition, Viscosity, and Eruption style magma has?

1. Composition of magma is the main control on a volcano's eruptive style, shape, types of materials, and potential hazards. 2. Some magma has fewer linked silicate chains and so it is relatively: "less viscous" (flows more easily). Lower viscosity allows magma to flow from the volcano in a more fluid lava flow. -restricting the flow of magma: makes it more viscous 3. High viscosity magma can trap gas, leading to "explosive pyroclastic eruptions" of gas-propelled volcanic ash, pumice, and rock fragments. -Composition controls viscosity, eruptive style, the shape of the volcano, and the rock types that compose that volcano.

What are some characteristics of a Composite volcano?

1. eruption column: when volcanic ash and pumice form when magma is blown apart by volcanic gases and can erupt high into the atmosphere. 2. pyroclastic flow: when some ash does not jet straight up but collapses down the side of the volcano as a dense, hot cloud of ash particles and gas. 3. landslides and mudflows: can be large mountains that collect rain or snow. Rain and snowmelt mix with loose ash and rocks on the volcano's flanks, causing a volcano-derived mudflow called a "lahar". 4. rocks: consist of alternating layers of pyroclastic flows, lava flows, and deposits from landslides and mudflows. 5. Lava domes and flows: can erupt from any level of a composite volcano. Lava may erupt from the summit crater or escape through vents on the volcano's sides or base. (move slowly/with difficulty) 6. shape: composite volcanoes display the classic volcano shape. have steep slopes

What areas around a Volcano have the highest risk?

1. proximity: the biggest factor determining potential risk is proximity, closeness to the volcano. The most hazardous place is inside an active crater. -potential risk decreases with increasing distance away from the volcano. 2. valleys: lava flows, small pyroclastic flows, and mudflows are channeled into valleys carved into the volcano and surrounding areas. 3. Wind direction: volcanic ash and pumice that are thrown from the volcano are carried farthest in the direction that the wind is blowing at the time of the eruption. -most regions have a "prevailing wind direction", so a greater hazard of falling materials exists in this direction from a volcano. 4. Particulars: these influence which part of the volcano is most dangerous. -steeper parts of a volcano pose special risks, and one side of a volcano may contain a dome that could collapse and form pyroclastic flows.

What features represent magma chambers within and beneath volcanoes?

1. volcanic necks: after the volcano erodes away, the solidified conduit can form this steep topographic feature. - a resistant and jointed volcanic conduit marks the center of the volcano. (exposing its internal architecture) 2. shiprock: a famous volcanic neck that rises above the landscape of New Mexico. -it consists of fragmented volcanic rocks (breccia), not originally inside a volcano, but instead were magma conduits that formed well beneath the surface. 4. some magma never reaches the surface, instead solidifying within a subsurface magma chamber. and commonly forming irregularly shaped mass of granite or other "intrusive rocks" -if a number of intrusions cover an area of more than 100 km^2 they form a: "batholith".

mesa

A broad, flat-topped and steep-sided, isolated hill or mountain.

calderas 11.5

A large volcanic depression that is typically circular to elongated shape and formed by collapse of a magma chamber. -most violent phenomena, they spread volcanic ash over huge areas. (more than one thousand cubic kilometers of magma)

vicosity

A measure of a material's resistance to flow

Pyroclastic eruptions

A volcanic eruption in which hot fragments that generally travels down the flanks of a volcano; also known as an ash flow.

What are the type of lava flows?

Aa lava: is a type of rough-surfaced lava flow, formed when the lava breaks apart into a mass of jumbled, angular blocks of hardened lava that tumble down the front of the flow as it moves. Pahoehoe: is a type of lava flow that has an upper surface with small billowing flows that form a "ropy" texture. -usually fed by a lava tube and grows as a series of lobes. -moves relatively smoothly and easily compared to "Aa flows".

What are the Relative Sizes of Different Types of Volcanoes?

Cinder cones and domes, which typically form during a single eruptive episode, are the smallest volcanoes. Shield volcanoes and composite volcanoes are much larger because they are constructed, layer by layer.

What hazards of associated with Eruptions of Cinder, Ash, and Gas?

Falling objects: most cinder falls back to the Earths ex. volcanic bombs, pose a severe hazard for anyone close to the erupting zone. Volcanic ash from Cinder cones: can bury nearby structures, and may cause breathing problems for people and livestock. Gases: gases such as carbon dioxide (CO2) causes asphyxiation if concentrated. -hydrogen sulfide (H2s), cause death by paralysis -gaseous sulfur dioxide (SO2), hydrochloric acid (HCI), sulfuric acid (H2SO4), and flourine compounds can destroy crops, kill livestock, and poison drinking water for people/animals. (can kill hundreds of people)

How do materials respond to "Differential Stress"? (three types)

Rocks, sediment, and other materials may be subject to three different types of differential stress: compression, tension, or shear. -the way in which rocks respond to these stresses varies as a function of depth because rock strength changes with depth, as pressure and temperature increases downward in the crust.

How does a caldera form?

The formation of a caldera and the associated eruption occur "simultaneously", the caldera subsides in response to rapid removal of magma from the underlying chamber. 1. The first stage is the generation of felsic magma. (the magma rises and accumulates in magma chambers) 2. Magma reaches the surface (at which point it is called lava) and eruptions begin. 3. The eruption forms columns and flows of pyroclastic material, much of which falls back into the caldera, creating a thick pile of ash. -steep caldera walls produce large blocks and clasts that become part of the caldera deposit. 4. As the eruption subsides, magma rises through fissures along the edges or in the caldera, erupting onto the surface as volcanic domes.

What regions have the highest risk for Volcanic eruption?

The largest concentrations of "composite volcanoes" is along the Pacific Ring of Fire. Most "shield volcanoes" occur along lines of islands and submarine mountains in the Pacific and other oceans.

How does viscosity affect gasses in Magma?

Viscosity: the resistance to flow, dictates how fast the magma can flow and how fast crystals and gas can move through the magma. When gas in a magma comes out of solution, movement of the resulting bubbles is resisted by the magma's viscosity. If the bubbles cannot escape, the magma is potentially more explosive.

Anticlines

a fold when rock layers warp up, in the shape of an A -the oldest rocks are in the center of the fold -where the layers are mostly tightly bent or reverse their direction of tilt is the "fold hinge"

Synclines

a fold where rock layers fold down in the shape of a V or U. -the youngest rocks are in the center of the fold. -the hinge of this fold is in the center, where the layers are mostly tightly folded and change direction. -the tilted parts of the hinge are called the "limbs" of the fold.

Faults (fractures expressed in Landscapes)

a fracture where rocks have lipped past one another. -can slip up and down, or slip sideways ***a fault displaces the rock on one side relative of the other side.

upper/lower brittle (strength of Continental Crust at depth)

a gradational boundary, or transition between the two. (occurs at a depth of 15 km and temps of 300 degress C) - strength decreases when pressure & temperature increases (weaker)

fissures

a magma-filled fracture in the subsurface, which typically solidifies into a dike, or a linear volcanic vent erupting onto the land surface

strain

a material can respond to stress by deforming internally- changing size or shape by ductile or brittle deformation. - a change of size or shape

displacement

a material is moved or displace, it can behave as a rigid object or can change shape as it moves.

force

a push or pull that causes, or tends to cause, change in the motion of a body.

Thrust fault 11.12 (main type of fault)

a reverse fault that has a gentle dip. -the rock above the fault is called a "thrust sheet" and is pushed up and over the block below the fault.

brittle deformation (strength of Continental Crust at depth)

a type of structural deformation that is characterized by breaking of material, such as by jointing, faulting, and the formation of tectonic breccia; typical of shallow crustal conditions.

ductile deformation (strength of Continental Crust at depth)

a type of structural deformation that is characterized by the material flowing as a solid, without fracturing; typical of the crust below about 15 km and of the asthenosphere.

shield volacanoes

a type of volcano that has broad, gently curved slopes constructed mostly of relatively fluid basaltic lava flows. -in shield volcanoes, magma rises through a fracture and erupts onto the surface from a long fissure. -eruptions also occur in more centralized vents. (overlie fissures)

risk (associated w/volcanoes)

an assessment of whether the hazard might have some societal impact ex. such as loss of life, damage to property, loss of employment

What is Deformation and how is it expressed in landscapes?

another tectonic process is deformation. Rock can be subjected to stress resulting from burial, tectonic activity, heating or cooling, and other processes. If the streses are strong enough, they cause rock to deform, move, rotate, and change shape. (or a combination of these)

Flood basalts

are balsaltic lava flows covering vast areas anf are commonly several kilometers thick.

Basaltic eruptions

at the beginning gases carry bits of lava into the air, forming a lava fountain. The airborne bits of lava cool and then fall around the vent as loose pieces of cinder. (may be followed by or accompanied by eruption of a basaltic lava flow)

rotation

can tilt the volume of material or spin it horizontally ex. rotation can be expressed by tilting, folding, or a partial spin of the material

What are some different types of volcanoes?

cinder cone: a relatively small type of volcano that is cone shaped and mostly composed of volcanic cinders (scoria); also known as a "scoria cone" shield volcano: a type of volcano that has a broad, gently curved slopes constructed mostly of relatively fluid basaltic lava flows. composite volcano: a common type of volcano constructed of alternating layers of lava, pyroclastic deposits, and mass-wasting deposits, including mudflows; also known as a stratovolcano. volcanic dome: a dome-shaped volcanic feature, largely composed of solidifies lava of felsic to intermediate composition.

lava flow (eruptions of lava)

created when magma erupts onto the surface and flows away from a vent

How are faults expressed in Landscapes?

deformation can fold rock layers on such a grand scale that a single fold occupies an entire mountain range. -can form at depth and at the surface. (classify/name folds based on their shape)

What features form when magma is injected as sheets? (Dike, Sill, & Laccolith)

dike: a sheetlike intrusion that cuts across any layers present in the host rocks. Most dikes are steep because the magma pushes apart the rocks, commonly in a horizontal direction, as it rises vertically and fills the resulting crack to form a dike. Sill: is an intrusion that is parallel to thin layers in the host rocks. most sills are gently inclined and form by pushing adjacent rocks upward rather than sideways. -contain steep fractures (columnar joints) formed by cooling of the sills after they solidified. Laccolith: is formed when ascending magma encounters gently inclined layers and begins squeezing parallel to them. The magma then begins inflating a lump- or bulge-shaped magma called a laccolith.

What are two different types of Pyroclastic Eruptions from the same Volcano?

eruption column: when volcanic ash and pumice form when magma is blown apart by volcanic gases and can erupt high into the atmosphere. pyroclastic flow: when some ash does not jet straight up but collapses down the side of the volcano as a dense, hot cloud of ash particles and gas.

How do gasses affect Magma?

ex. soda can exploding 1. The dissolved gas was always in the liquid, but it only became visible when you opened the top and released the pressure that held the gas in solution. 2. Magma, like the soda, contains some dissolved gases, including: H20 (water vapor), C02 (carbon dioxide), and SO2 (sulfur dioxide). These gases have a critical effect on eruption style and help the magma rise toward the surface. 3. Confining pressure at depth keeps most of the gases in solution and keep most of the gases in solution and keeps bubbles from forming.

Basaltic lava flows

fluid basaltic lava pours from the vent and flows downhill. -sometimes the lava fills up and overtops the crater in the cinder cone.

Dome

form when layers are uplifted in a circular or elliptical area and dip away in all directions

Basin

formed, by folding, is the opposite of a dome. -layers dip toward the center of the basin from all directions. ***center of the basin: younger layers

lava dome (eruptions of lava)

forms from the eruption of highly viscous lave. The high viscosity of the lava causes the lava to pile up in a dome-shaped mass.

pillows

forms when fluid lava erupts into water, the lava grows forward as small, individual lumps that form rounded shapes -are reliable evidence that lava erupted into water.

Lava tubes

forms when the surface of a lava flow solidifies to form an insulation rood over the hot, still-moving interior of the flow.

Shear

if stresses on the edge of a block were applied in opposite directions. - shearing in shallow parts of the crust usually forms a "fault" - depending on the direction of shearing, one block can move up, down, or sideways relative tho the block on the other side of the fault.

Normal fault 11.12 (main type of fault)

is when a block above the fault moves down relative to the block below the fault. -forms when the rock units are pulled apart and lengthened ***dips to the right

Strike-Slip fault 11.12 (main type of fault)

is when rocks along a fault move with a side-to-side motion

Reverse fault 11.12 (main type of fault)

is when the block above the fault moves up relative to the block below the fault. - a reverse fault forms as a result of horizontal compression and shortens the rock units in a horizontal direction. ***dips to the right

How do materials respond to "force" and "stress"? (three things can happen)

materials within Earth are subjected to forces from the weight of overlying rocks, from tectonic forces pushing or pulling on the rocks, from cooling and heating, and from pressured fluids (water/magma) - if force is concentrated (high stress), a rock can break or otherwise deform. - block of material may remain unchanged if subjected to only a small amount of stress. If imposed stresses are greater, the material may be: displaced, rotated, or strained

When do most Earthquakes occur?

most occur when forces cause two parts of Earth's crust to shift abruptly relative to one another. ex. such movement can uplift a mountain range, down drop a valley, San Andreas fault.

How are Magmatic Conduits exposed?

not all magma reaches the surface and erupts in a volcano. Instead, most magma solidifies at depth, forming bodies of igneous rock called intrusions. -intrusions have a sheetlike, pipelike, or even lumpy geometry, and where exposed at the surface from distinctive landscape features.

How do we assess the Danger posed by a Volcano?

shape: volcanoes with steep slopes, such as composite volcanoes are more dangerous, because they form from potentially explosive, vicious magma and are also prone to landslides. -volcanoes that have relatively gentle slopes, such as most shield volcanoes result from less explosive basaltic eruptions. Types of volcanic materials: the types of materials on a volcano indicate the magma composition and style of eruption. -very dangerous if it contains deposits formed by pyroclastic flows. Age & History: If the volcano has not erupted for a long time, maybe it is a dormant (not active). clues to indicate a volcano's history is: oral histories from nearby people, isotopic measurements on volcanic units(accurate indication of a volcano's age.

stress

the amount of force divided by the area where the force is applied

hazard (associated w/volcanoes)

the existence of a potentially dangerous situation or event ex. potential landslide of a steep slope or lava flow erupting form a volcano

internal processes

those that originate deep beneath the surface and are powered mostly by Earth's internal heat

What are some characteristics of a Volcanic Dome?

volcanic domes form when viscous lava mounds around a vent. 1. a rubble-covered dome, their outer appearance consists of angular, broken pieces 2. Domes mostly grow from the inside as magma injects into the interior of the dome, new material causes the dome to expand upward and outward. -this process creates the blocks of rubbly, solidified lava that coat the outside of the dome. 3. domes also grow as magma breaks through to the surface and flows outward as thick, slow-moving lava. can collapse into angular blocks and ash. 4. Domes can be partially destroyed when steep flanks of the dome collapse and break into a jumble of blocks and ash that flow downhill. (ex. Mount Unzen, Japan)

Felsic magmas

w/ abudant quartz and feldspar-contain a lot of silica (relatively viscous). The high viscosity prevents gas from escaping easily. -gas builds up in the magma and, when it expands, greatly increases the pressure on the surrounding rock. (causing explosive eruptions)

Mafic magmas

w/ abundant iron and magnesism-are less viscous. (gas bubbles can escape easily) -this can lead to a fairly nonexplosive eruption, such as this basaltic lava flow that flows smoothly downhill from the vent.

Joints (fractures expressed in Landscapes)

when fractures form as simple "cracks" representing places where the rock has pulled apart by a small amount.

Tension

when stress is directed outward, pulling the rock - tension can form fractures that help the rock stretch as it is pulled apart -fluids, if present, can deposit minerals in the fracture, forming a "vain". -tension can also cause slip along fractures, pulling one block past another.

Compression

when stress pushes in on rock -compression in shallow levels of the crust can cause rocks to fracture and slip past one another. -a fracture along which two rock masses slip past each other is a "fault"