geology exam #2

A horizon

Largely mineral matter yet biological activity is high and humus is generally present.

horizons

vertical soil zones or layers; make up the soil profile

solum

"true soil", O, A, E, B horizons together

intrusive igneous rocks

(plutonic rocks). Magma that crystallizes at depth. These rocks are observed at the surface and locations were uplifting and erosion has stripped away the overlying rocks. Examples White Mountains, New Hampshire; Stone Mountain, Georgia; the Black Hills of South Dakota; Yosemite National Park.

steps of coal formation

1. accumulation of plant remains 2. formation of peat 3. formation of lignite and bituminous coal 4. formation of anthracite coal

coquina

Biochemical limestone, quartz rock composed of poorly cemented shells and shell fragments.

O horizon

Consists largely of organic material. This is in contrast to the layers beneath it which consists mainly of mineral matter. Upper portion is primarily plant litter such as loose leaves and other organic debris. Lower portion is made up of partly decomposed organic matter (humus) in which plant structures can no longer be identified. Teeming with microscopic life

humus

Decayed remains of animal and plant life

facies

Different parts of each layer of sediment possess a distinctive set of characteristics that reflects the conditions in a particular environment

continental environments

Dominated by the erosion and deposition associated with streams.. . In arid regions wind takes on greater importance And some cold regions moving masses of glacial ice replace running water as dominant process. streams erode more land and transport and deposit more sediment than any other process.

soil taxonomy

Emphasizes the physical and chemical properties of the soil profile and is organized on the basis of observable soil characteristics. There are six hierarchical categories of classification ranging from order , the broadest Category, to Series

salt flats

Following rains or periods of snowmelt in the mountains, streams flow from the surrounding mountains into an enclosed basin. As water evaporates, Salt Flats form

1. accumulation of plant remains

First there is an accumulation of plant remains. Special conditions are required for such accumulations because dead plants readily decompose when exposed to the atmosphere or other oxygen-rich environment. One environment that allows for the buildup of plant material is a swamp because stagnant swamp water is oxygen deficient. Plants are attacked by certain bacteria that partly decompose the organic material and liberate oxygen and hydrogen.. As they escape the percentage of carbon gradually increases

3. formation of lignite and bituminous coal

Higher temperatures bring about chemical reactions within the plant materials and yield water and organic gases. As load increases from more sediment on top of the developing coal, the water and volatiles are pressed out and the proportion of fixed carbon increases. The greater the carbon content the greater the coals energy ranking as a fuel. Deeper burial transforms lignite into a harder more compacted black rock called bituminous coal.

mud cracks

Indicate that the sediment in which they were formed was alternately wet and dry. When exposed to air, wet mud dries out and shrinks producing cracks. Associated with such environments as tidal Flats, shallow Lakes , desert basins

floodplains

Large quantities of sediments are dropped when floodwaters periodically inundate broad flat Valley floors

regolith

Layer of rock and mineral fragments produced by weathering not the same as soil

cross-bedding

Layers within a bed of sedimentary rock that are inclined to the horizontal. Most characteristic of sand dunes, river deltas, and certain stream channel deposits

E horizon

Light-colored layer that contains little organic material. As water percolates downward through this Zone finer particles are carried away (eluviation). Water percolating downward also dissolve soluble in organic soil components and carries them to deeper zones (leaching)

4. formation of anthracite coal

Lignite and bituminous coal are sedimentary rocks. However when sedimentary layers are subjected to the folding and deformation associated with mountain building the heat and pressure cause a further loss of volatile and water thus increasing the concentration of fixed carbon. This changes bituminous coal into anthracite , very hard shiny black metamorphic rock. It is a clean-burning fuel but expensive to get

inorganic limestone

Limestones having an inorganic origin form when chemical changes or high water temperatures increase the concentration of calcium carbonate to the point that it precipitates

compaction

Most common physical diagenetic change. a process of lithification. as sediment accumulates, the weight of overlying material compresses the deeper sediments. The deeper a sediment is buried the more it is compacted and the firmer it becomes . As grains are pressed closer and closer there is considerable reduction in pore space

cementation

Most important process by which sediments are converted to sedimentary rock. Involves crystallization of minerals among the individual segment grains. Groundwater carries ions in solution, and gradually crystallization of new minerals from these ions takes place in the pore spaces cementing the clasts together. Reduces its porosity. Calcite silica and iron oxide are the most common cements.

topsoil

O & A horizons

C horizon

Partially altered parent material.

graded beds

Particles within a single sedimentary layer gradually change for from course at the bottom to fine at the top. Most characteristic of Rapid deposition from water containing sediments of varying sizes. When a current experiences a rapid energy loss, the largest particle particles settle first followed by successively smaller grains. Deposition of a graded bed is most often associated with a turbidity current, a mass of sediment-choked water that is denser than Clear water and that moves downslope along the bottom of a lake or an ocean

bedding planes

Relatively flat surfaces along which rocks tend to separate or break. Changes in grain size or in the composition of the sediment being deposited can create bedding planes. Each one marks the end of one episode of sedimentation and the beginning of another.

ripple marks

Small waves of sand that develop on the surface of a sediment layer by the action of moving water or air

chalk

Soft porous Rock made up almost entirely of the hard parts of microscopic marine organisms. Example: chalk deposit along the Southeast coast of England

parent material

Source of the weathered mineral matter from which soil develops, major factor influencing newly forming soil. Can either be the underlying bedrock or a layer of unconsolidated deposits. When parent material is bedrock the soils are called residual soils. Those developed on unconsolidated sediments are called transported soil. Transported soil form in place on the parent material that have been carried from elsewhere and deposited by gravity, water, wind, or ice.

hydrolysis

The silicates are decomposed primarily by the process of hydrolysis. Basically the reaction of any substance with water. Presence of CO2 accelerates the process (dissolves in water to form carbonic acid)

dissolution

Types of chemical weathering. Presence of even a small amount of acid dramatically increases the corrosive force of water, thus causing dissolution

spheroidal weathering

Weathering attacks edges from two sides and corners from three sides , these areas wear down faster than a single flat surface. Gradually, sharp edges and Corners become smooth and rounded

alluvial fan

Where rapid streams emerge from a mountainous area onto a flat surface a distinctive cone shaped accumulation of sediment forms

soil

Where the geosphere, atmosphere, hydrosphere, and biosphere meet

fissility

ability to split into thn layers along closely spaced planes

diagenesis

all the changes (short of metamorphism) that take place in texture, composition and other phys. properties after sediments are deposited

agate

banded form of chert; precipitates in concentric rings within voids of a rock

transitional environments

beaches, tidal flats, spits, bars, barrier islands, lagoons, deltas

sedimentary rock cycle

begins w/ weathering, of preexisting rocks of all types. soluble constituents carried away by runoff and groundwater. solid particles moved downward by gravity. sediment is transported by something. deposition occurs. sediments are lithified by compaction and cementation.

limestone

chemical sed. rock, most abundant, composed mainly of calcite

chert

chemical sed. rock; Very Compact and hard rocks made of microcrystalline quartz. Flint, Jasper agate, petrified wood. deposits either bedded cherts or nodules

dolostone

chemical sed. rock; composed of dolomite. will not visibly react to hydrochloric acid. origin unknown

petrified wood

chert that is made when silica-rich material such as volcanic ash buries trees

arkose sandstone

contains 25% or more of feldspar

sorting

degree of similarity in particle size in a sed. rock gives clues about depositing current

leaching

depletion of soluble materials from upper soil in E horizon

breccia

detrital like conglomerate, but large particles are angular rather than rounded

shale

detrital rock consisting of silt and clay size particles. over 1/2 of all sed. rocks. result of gradual settling from quiet non-turbulent currents. made up of laminae (thin layers). mudstone and siltstone lack fissility. shale forms gentle slopes

conglomerate

detrital sed. rock that consists largely of gravels, poorly sorted

sandstone

detrital. sand-size grains. 2nd most abundant sed. rock. Quartz is predominant mineral. clues of their origin: sorting, particle shape, mineral composition. quartz, arkose, graywacke.

clays

fine-grained minerals with sheetlike crystalline structures similar to the micas

organic sedimentary rocks

forms from carbon-rich remains of organisms. Ex: coal.

evaporites

in seas which only had narrow connections to the open ocean, seawater continually moved into the bay to replace water lost by evaporation. Eventually waters of the bay became saturated and salt deposition began. Such deposits are evaporites. ex: rock salt,, rock gypsum (halite and gypsum are the minerals precipitated)

presence of feldspar and micas in sedimentary rocks

indicates that erosion & deposition were fast enough to preserve some of the primary source rock before they could be decomposed

travertine

inorganic limestone; Commonly seen in caves. as ground water droplets become exposed to the air in a Tavern some of the carbon dioxide dissolved in the water escapes causing calcium carbonate to precipitate

oolitic limestone

inorganic limestone; Composed of small spherical grains call ooids. ooids form in shallow Marine Waters as Tiny Seed particles are moved back and forth by currents. as the grains are rolled about in warm water which is supersaturated with calcium carbonate, they become coated with layer upon layer of the chemical precipitate.

strata/beds

layers of sediment; Single most common and characteristic feature in sedimentary rocks. Each stratum is unique. Variations in texture , composition, and thickness reflect the different conditions under which each layer was deposited

differential weathering

masses of rock do not weather uniformly, various factors

graywacke

more than 15% of rock volume is matrix

products of potassium feldspar weathering

most abundant: kaolinite (clay mineral), soluble salt, some silica

crystalline texture

nonclastic; Minerals form a pattern of interlocking crystals. Examples are those rocks deposited when saline water evaporates. Consist of intergrown crystals and some may resemble igneous rocks, which are also crystalline. found in some chemical sed. rocks

2. formation of peat

partial decomposition of plant remains in an oxygen-poor swamp creates a layer of peat. Peat slowly changes to lignite a soft brown coal. Burial increases temperature of sediments as well as pressure on them.

basis for distinguishing detrital sed. rocks

particle size

products of quartz weathering

quartz grains, silica in solution

jasper

red variety of chert, color comes from iron oxide

factors for rate of weathering

rock characteristics and climate. differential weathering

clasts

rock fragments

detrital sedimentary rock

rocks formed from an accumulation of material that originates and is transported as solid particles derived from both mechanical and chemical weathering. Clay minerals and quartz are chief constituents. also feldspar and micas

oxidation

rusting; Occurs when oxygen combines with iron to form iron oxide. Electrons are lost from one element during the reaction , iron was oxidized because it lost electrons to oxygen. Addition of water greatly speeds the reaction

chert nodules

secondary cherts/replacement cherts; most often occur within beds of limestone

chemical sedimentary rocks

sediment's source is soluble material produced largely by chemical weathering. ions in solution are precipitated by inorganic/biological processes

B horizon

subsoil; Where much of the material removed from the E horizon by eluviation is deposited. is often referred to as the zone of accumulation. Accumulation of fine clay particles enhances water retention in the subsoil. In extreme cases clay accumulation can form a very Compact and impermeable layer called hardpan

clastic texture

texture of sed. rock; Rocks with clastic texture consist of discrete fragments and particles that are cemented and compacted together. Although cement is present in the spaces between particles these openings are rarely filled completely. All detrital Rocks Have A clastic texture. Some chemical sedimentary rocks exhibit this texture

laminae

thin layers in shale

other controls of soil formation

time, climate, plants and animals, topography

flint

type of chert, dark color results from its organic matter

carbonate reefs

type of limestone. coral secrets calcium carbonate

eluviation

washing out of fine soil components in E horizon

crystal settling

This process occurs when the earlier formed minerals are denser than the liquid portion and sink toward the bottom of the magma chamber. When the remaining melt solidifies either in place or in another location, if it migrates into fractures in the surrounding rocks, it will form a rock with a mineralogy much different from the parent magma. Accounts for the great diversity of igneous rocks

solid components of magma

crystals of silicate materials. magma body cools, size and number of crystals INCREASE. during last stage of cooling, magma body is like a "crystalline mush"

resurgent dome

distinctive characteristic of Yellowstone-type large caldera-forming eruptions; Slow upheaval of floor of caldera which produces a central elevated region

rhyolite

fine-grained equivalent of granite and it's composed essentially of the light coloured silicate. It's color is buff to pink or occasionally light gray. Deposits are less common

dissolved gases affects viscosity

loss of gases renders magma more viscous

lava tubes

made by pahoehoe flows, Previously conduits for carrying lava from an active vent to the flow's leading edge. They form in the interior of a lava flow , where the temperature remains high long after the surface cools and hardens. They serve as insulated pathways that facilitate the advance of a lava great distances from its source

basaltic composition

mafic rocks. Rocks that contain at least 45% dark silicate minerals and calcium-rich plagioclase feldspar but no quartz . Contain a high percentage of ferromagnesian minerals. Typically darker and denser than granitic rocks. Make up the ocean floor as well as many of the volcanic islands located within the ocean basins . Basalt also forms extensive lava flows on the continent

viscosity

magma's mobility, more viscous = greater resistance to flow

largest shield volcano

mauna loa

composition affects viscosity

more silica in magma, greater its viscosity

dikes

type of later vertical rock between older layers of rock. Technically, it is any geologic body which cuts across: flat wall rock structures, such as bedding. massive rock formations, usually igneous in origin.A type of tabular intrusive body . Produced when magma is forcibly injected into a fracture or zone of weakness . Discordant bodies that cut across bedding surfaces or other structures in the country rock . Serve as tabular conduits that transport magma . Typically shallow features, occurring where the country rocks are sufficiently brittle to fracture . Tend to form in roughly parallel groups called dike swarms. Can also radiate from an eroded volcanic neck, like spokes on a wheel. Frequently weather more slowly than the surrounding rock. Consequently when exposed by erosion, dikes tend to have a wall like appearance

formation of basaltic magma

Basaltic magmas that originated from partial melting of mantle rocks are called primary or primitive magma because they have not yet evolved. Partial melting that produces mantle-derived magmas may be triggered by a reduction in confining pressure during the process of decompression melting. This can occur where hot mantle rock ascends as part of slow-moving convective flow at mid-ocean ridges. Also generated at subduction zones, where water driven from the descending slab of oceanic crust promotes partial melting of the mantle rocks that lie above

salt crystal growth

Sea spray from breaking waves or salty groundwater penetrates crevices and pore spaces in Rock. As water evaporates, salt crystals form. As these crystals gradually grow larger they weaken the Rock by pushing apart the surrounding grains or enlarging tiny cracks.

block lava

Short thick flows, upper surface consist largely of massive detached blocks. These blocks have slightly curved smooth surfaces rather than rough and spiny

continental volcanic arc

Slabs of oceanic lithosphere are subducted under continental lithosphere and produce continental volcanic arcs. Continental crust is much thicker and is composed of rocks having higher silica content. Magma generated in the mantle may change from a fluid basaltic magma to a silica-rich andesitic or rhyolitic magma as it moves up through the continental crust

stocks

Smaller plutons. Many stocks appear to be portions of much larger intrusive bodies that would be classified batholiths if they were fully exposed

lava

Molten rock that reaches Earth's surface

extrusive igneous rocks

(volcanic rocks). Igneous rocks that form when molten rock solidifies at the surface. Abundant in western portions of the Americas, where they make up the volcanic peaks of the Cascade Range and the Andes Mountains. In addition, many oceanic islands including the Hawaiian chain and Alaska's Aleutian Islands are composed almost entirely of extrusive igneous rocks

Bowen's reaction series

A schematic description of the order in which minerals form during the cooling and solidification of magma and of the way the newly formed minerals react with the remaining magma to form yet another series of minerals. Bowen demonstrated that if the solid components of a magma remain in contact with the remaining melt, they will chemically react and change mineralogy. Minerals crystallize from magma in a systemic fashion

lahar

A type of fluid mud flow generated by large composite cones. Occur when volcanic debris becomes saturated with water and rapidly move down steep volcanic slopes following stream valleys. Some are triggered when magma near the surface of a glacially clad volcano, causing large volumes of ice and snow to melt. May occur even when a volcano is not erupting.

mechanical weathering

Accomplished by physical forces that break rock into smaller and smaller pieces without changing the Rock's mineral composition. Includes Frost wedging, salt crystal growth, expansion resulting from unloading, biological activity

formation of granitic magmas

Although granitic magmas can arise through magmatic differentiation of andesitic magmas , most granitic magmas probably form when hot basaltic magma ponds below continental crust. This process is thought to have been responsible for the volcanic activity around Yellowstone National Park

assimilation

As magma migrates through the crust, it may incorporate some of the surrounding rock in a process called assimilation. In the near surface environment where rocks are brittle the magma pushes upward, as it causes numerous fractures in the overlying rock. The force of the injected magma is often sufficient to dislodge blocks of foreign rock which melts and are incorporated into the magma body

explosive eruptions- lava fountains

As magma rises a reduction in pressure occurs and the dissolved gases begin to separate from the mount forming tiny bubbles. When fluid basaltic magma erupts the pressurized gas is readily escape. Gases can quickly expand to occupy hundreds of times their original volume. Occasionally these gases propel incandescent lava hundreds of meters into the air producing lot of fountains. These fountains are usually harmless and generally not associated with great loss of life or property.

cinder cones

Built from ejected lava fragments that begin to harden in flight to produce the vesicular rock scoria. These fragments range in size from fine ash to bombs that may exceed one meter in diameter. Tends to have a basaltic composition. Some produce extensive lava fields. Lava flows generally form in the final stages of the volcanoes lifespan . Love I usually flows out from unconsolidated base of cone rather than from the crater. High angle of repose. Large deep crater. Most are produced by a single short-lived eruptive event. ex: Paricutin, Mexico

ring of fire

Circum Pacific belt, consist mainly of composite cones that emit volatile rich magma that has an intermediate and andesitic composition and occasionally produces big eruptions

granite

Coarse-grained rock composed of about 10 to 20% quartz and roughly 50% potassium feldspar.

caldera-forming eruptions (yellowstone-type)

Colossal proportions, ejecting huge volumes of pyroclastic material , mainly in form of ash and pumice fragments. Destroy most living things in their path. Fragment fused together forming a welded tuff that closely resembles a solidified lava flow. Eruptions are brief. So large and poorly defined that many remain undetected until now

vesicular texture

Common features of many extrusive rocks are the voids left by gas bubbles that escaped as lava solidifies. These openings are called vesicles. Rocks that exhibit a vesicular texture often form in the upper zone of a lava flow where cooling occurs rapidly enough to preserve the openings produced by the expanding gas bubbles

ultramafic

Composed almost entirely of ferromagnesian minerals, rare at Earth's surface, peridotite is the main constituent of the upper mantle

magma mixing

Composition of magma can be altered through magma mixing. May occur during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body . Once they are joined, convective flow stirs the two magmas, generating a single mass that has an intermediate composition

andesitic/intermediate composition

Contain at least 25% dark silicate minerals, mainly amphibole, pyroxene, and biotite mica, with the other dominant mineral being plagioclase feldspar. Associated with volcanic activity that is typically confined to the seaward margin of the continents and on volcanic island arcs such as the Aleutian chain

other examples of unloading/rock expansion

Contraction during the crystallization of magma creates fractures, still others are produced by tectonic forces during mountain building. Fractures produced by these activities form a definite pattern and are called joints

crystallization

Cooling reverses the events of melting. As the temperature of the liquid drops, ions pack more closely together at the rate of movement slows. When they are cooled sufficiently, the forces of the chemical bonds will again can find the ions to an orderly crystalline arrangement. When magma cools, it is generally the silicon and oxygen atoms that link together first to form silicon-oxygen tetrahedra, the basic building blocks of the silicate minerals. As magma continues to lose heat to its surroundings, the tetrahedra join with each other and with other atoms to form embryonic crystal nuclei. Slowly each nucleus grows as ions lose their mobility and joined the crystalline Network

obsidian

Dark colored glassy rock that usually formed when highly silica-rich lava cools quickly at Earth's surface. Arrangement of ions in a glass is unordered. Not composed of minerals in the same sense as most other rocks. Chemical composition that is roughly equivalent to that of a light colored igneous rock granite, not like dark rocks such as basalt. Obsidian's dark color results from small amounts of metallic ions in an otherwise relatively clear glassy substance

parasitic cone

During early stages of growth most volcanic discharges come from a central summit vent. As volcano matures, material tends to be emitted from fissures that develop along the flanks or at the base of the volcano. Continued activity form of flank eruption may produce one or more parasitic cones

glassy texture

During some volcanic eruptions molten rock is ejected into the atmosphere where it is quenched and cools quickly to become a solid. Rapid cooling of this type may generate rocks having a glassy texture. Glass results when unordered ions are frozen in place before they are able to unite into an orderly crystalline structure . Obsidian is a common type of natural glass.

quiescent eruptions

Eruptions that involve very fluid basaltic lavas such as the eruption of Kilauea on Hawaii Big Island are often triggered by the arrival of a new batch of molten rock into a near-surface magma chamber.. This event can usually be detected because the summit of the volcano begins to inflate and rise months or even years before an eruption. injection of a fresh supply of hot molten rock heats And remobilizes the semi-liquid magma chamber. Swelling of magma chamber fractures the rock above allowing the fluid magma to move upward along the newly formed opening generating outpourings of lava for weeks months or years

pahoehoe

Exhibit smooth surfaces that sometimes resemble the twisted braids of ropes, hotter and more fluid

flood basalts

Extrusions in which numerous fissure eruptions have buried the landscape creating a lava plateau. Columbia Plateau is an example

magmatic differentiation

Formation of one or more secondary magmas from a single parent magma. Ex: Palisades Sill

welded tuff

Formed when hot ash falls and glassy shards compact and fused together. Sheets cover vast portions of the western United States , I kind of pyroclastic materials

volatiles

Gaseous components of magma. materials that vaporize at surface pressure. Most common volatiles found in magma are water vapor, carbon dioxide, and sulfur dioxide, which are confined by the immense pressure exerted by the overlying rocks . These gases tend to separate from the melt as it moves toward the surface from a high to a low pressure environment. As gases build up, they may eventually propel magma from the vent. When deeply buried magma bodies crystallized, the remaining volatile collect as hot, water-rich fluids that migrate through the surrounding rocks

shouldering

Great depths, where rock is ductile, a mass of buoyant rising magma can forcibly make room for itself by pushing aside the overlying rock. As magma continues to move upward, some of the host rock that was displaced will fill in the space left by the magma body as it passes

aa flows

Have surfaces are rough jagged blocked with dangerously sharp edges and shiny projections.

eruption columns

Highly viscous magmas expel particles of fragmented lava and gases at nearly supersonic speeds that evolve into buoyant plumes called eruption columns.

porphyritic texture

If molten rock containing some large crystals moves to a different environment, for example, by erupting at the surface, the remaining liquid portion of the lava cools more quickly. Resulting rock has large crystals embedded in a matrix of smaller crystals. The large crystals are referred to as phenocrysts. Matrix of smaller crystals is called groundmass. A rock with a porphyritic texture is termed a porphyry

granitic composition

Igneous rocks in which light colored silicates , quartz and potassium feldspar, are the dominant minerals. Geologist also referred to Granitic rocks as being felsic , a term derived from feldspar and silica. Rich in silica , major constituents of the continental crust

aphanitic (fine-grained) texture

Igneous rocks that form at the surface or a small intrusive masses within the upper crust where cooling is relatively rapid exhibit fine-grained texture. The crystals are so small that individual minerals can only be distinguished with the aid of a polarizing microscope. Light, intermediate, or dark in color.

exfoliation dome

In sheeting, continued weathering eventually causes the slabs to separate and spall off. Examples : Stone Mountain, liberty cap in Yosemite National Park

diapirs

In the upper mantle and lower crust where temperatures and pressures are high, rock is able to flow. In this setting boy and magma bodies are assumed to rise in the form of inverted. Drop shaped masses with rounded heads and tapered tails (diapirs)

partial melting

Incomplete melting of rocks, a process that produces most magma

geothermal gradient

Increase in temperature with depth. Averages about 25 degrees Celsius per kilometer in the upper crust.

pyroclastic texture

Injected particles during explosive volcanic eruptions might be very fine ash, molten blobs, or large angular blocks to and from the walls of event during an eruption. Igneous rocks composed of these rock fragments have fragmental texture. Common type is welded tuff , composed of fine fragments of glass that remained hot enough to fuse together. Their textures often resemble those exhibited by sedimentary rocks rather than those associated with igneous rocks

diorite

Intrusive equivalent of andesite. coarse-grained rock that looks somewhat like gray granite. Contains little or no visible quartz crystals and have a higher percentage of dark silicate minerals than granite. Mineral makeup is primarily plagioclase feldspar and amphibole. Salt and pepper appearance

gabbro

Intrusive equivalent of basalt. Tends to be dark green to black in color and composed primarily of pyroxene and calcium rich plagioclase feldspar. Uncommon in continental crust, makes up a significant percentage of oceanic crust

chemical weathering

Involves a chemical transformation of rock into one or more new compounds; water most important agent. Processes: dissolution, oxidation, hydrolysis

batholiths

Largest intrusive igneous bodies. Occur as mammoth linear structures several hundred kilometers long and up to 100 kilometers wide. Can cover a large area. recent gravitational studies indicate that most are less than 10 kilometers thick. Typically composed of felsic and intermediate rock types and are often referred to as granite batholiths. Consist of hundreds of plutons that intimately crowd against or penetrate one another.

melt

Liquid component of magma. Composed mainly of mobile ions of the 8 most common elements found in Earth's crust, silicon and oxygen, along with lesser amounts of aluminum, potassium, calcium, sodium, iron, magnesium

andesite

Medium gray fine-grained rock typically of volcanic origin. Numerous volcanoes in the Andes Mountains are composed of this rock type. Commonly exhibits a porphyritic texture. May also resemble rhyolite so its identification usually requires microscopic examination to verify mineral makeup

surges

Occasionally powerful hot blasts that carry small amounts of ash separate from the main body of a pyroclastic flow. Low-density clouds, can be deadly but seldom have sufficient force to destroy buildings

columnar jointing

Occurs when igneous rocks cool and develop shrinkage factors that produce elongated pillar like columns that most often have six sides. aka giants causeway

formation of andesitic magmas

One way is when a rising mantle-derived basaltic magma undergoes magmatic differentiation as it slowly makes its way through the continental crust. As basaltic magma solidifies, the silica-poor ferromagnesian minerals crystalize first. If these iron-rich components are separated from the liquid by crystal settling the remaining melt will have an andesitic composition. These evolved magmas are termed secondary magmas. Andesitic magmas can also form when rising basaltic magmas assimilate crustal rocks that tend to be silica-rich. Partial melting of basaltic rocks is yet another way.

magma

Parent material for igneous rocks. Consists of three materials- a liquid component, as solid component, & a gaseous component

weathering

Physical breakdown and chemical alteration of rock at or near Earth's surface. Basic part of the rock cycle.

xenoliths

Plutons that contain suspended blocks of country rock. Evidence to support stoping

shield volcano

Produced by the accumulation of fluid basaltic lavas and exhibits the shape of a broad slightly domed structure that resembles a warrior's shield. Most begin on the ocean floor as seamounts a few of which grow large enough to form volcanic islands. Most small oceanic islands are either a single shield volcano or the coalescence of two or more shields. Examples are Canary Islands, Hawaiian Islands, the Galapagos, Easter Island

scoria

Pyroclastic material, volcanic rock containing many holes or voice called vesicles. Black to reddish brown in color and basaltic or andesitic in composition

bombs

Pyroclastic materials larger than 64 millimeters in diameter and dejected as incandescent lava . Semi-molten upon ejection , they often take on a streamlined shape as they hurtled through the air.

blocks

Pyroclastic materials larger than 64 million millimeters in diameter, made of fragments of already hardened lava

volcanic pipe

Rare type of conduit. Carries magma that originated in the mantle at depths that may exceed 93 miles. Gas-laden magmas that migrate through pipes travel rapidly enough to undergo minimal alteration during their ascent

pegmatitic texture

Under special conditions , exceptionally coarse grained igneous rocks, called pegmatite may form. Most of the crystals are larger than one centimeter in diameter. Most occur at small masses or thin veins within or around the margins of large intrusive igneous bodies. Pegmatite form late in the crystallization of magma, when water and other materials such as carbon dioxide, chlorine, and flooring, make up an unusually high percentage of the amount . Because ion migration is enhanced and these fluid rich environment, the crystals that form are abnormally large . Composition is similar to granite

texture

Used to describe the overall appearance of a rock based on the size shape and arrangement of its mineral grains , not how it feels to touch. Reveals a great deal about the environment in which the rock formed

basalt

Very dark green to black, fine grained rock composed primarily of pyroxene and calcium rich plagioclase feldspar with lesser amounts of olivine & amphibole. When it is porphyritic, basalt commonly contains small light-colored feldspar phenocrysts or green glassy appearing olivine grains embedded in a dark groundmass . Most common extrusive igneous rock. Many volcanic islands are composed mainly of basalt. Upper layers of the oceanic crust consists of basalt.

caldera

Very large circular depression in some volcanoes with a diameter greater than 1 kilometer. Most are formed by (1) the collapse of the summit of a large composite volcano following an explosive eruption of silica-rich pumice and ash fragments , Crater Lake type, (2) or the collapse of a large area caused by the discharge of colossal volumes of silica-rich pumice, , Hawaiian type, (3) or the collapse of the top of a shield volcano caused by subterranean drainage from a central magma chamber, caldera and ash along ring fractures , Yellowstone type

pumice

Volcanic rock with a glassy texture that forms when large amounts of gas escape through silica-rich lava to generate a gray frothy mess. Many samples of pumice will float when placed in water. pumice and obsidian can often be found in the same rock mass where they exist in alternating layers

volcanic island arcs

Volcanism at convergent plate margin. Develops roughly parallel to the associated trench , can be constructed on oceanic as well as continental lithosphere. Examples are the Aleutians , the Tongas and the Marianas

volcanic necks

When a volcano becomes inactive, congealed magma become preserved in the feeding conduit of the volcano as a cylindrical mass. All hope volcanoes overtime succumb to forces of weathering and erosion. Rock occupying the volcanic conduit may remain standing above the surrounding terrain long after the cone has been worn away. Higher than most skyscrapers

fissure

crack in earth's surface; Greatest volume of volcanic material is extruded from these. Rather than building cones they most often emit fluid basaltic lavas that blanket wide areas.

sheeting

When large masses of igneous rock , particularly Granite, are exposed by erosion, concentric slabs begin to break loose. This takes place due to the great reduction in pressure that occurs as The overlying Rock is eroded away, a process called unloading. As overburden is removed, outer parts of the Granite Mass expand more than the rock below and separate from the rock body. Continued weathering creates an exfoliation dome

phaneritic texture

When large masses of magma slowly crystallized at great depth, they form igneous rocks that exhibit a coarse grained texture. Consist of a mass of intergrown crystals that are roughly equal in size and large enough so that the individual minerals can be identified without the aid of a microscope .

lava domes

When lava is so viscous that it can hardly flow at all, it is squeezed out of event and produces a dome-shaped mass. Usually only a few tens of meters high , in a variety of shapes that range from pancake-like to steep sided plugs pushed upwards like pistons. Most grow over a period of several years following an explosive eruption of silica-rich magma . Example is the dome that begin to grow in the crater of Mount st. Helens. Collapse of long lava domes often produce powerful pyroclastic flows

pillow lavas

When outpourings of lava occur on the ocean floor the flows outer skin quickly freezes to form obsidian. However interior lava is able to move forward by breaking through the heart and surface. this process occurs over and over and the result is a lava flow composed of numerous tube like structures stopped one atop the other

explosive eruptions

When the pressure of the expanding magma body exceeds the strength of the overlying Rock, fracturing occurs. As magma moves up the rock fractures , a further drop in confining pressure causes more gas bubbles to form and grow. This chain reaction can cause an explosive event in which magma is literally blown into fragments, ash and pumice, that are carried to great heights by the hot gases. When magma in the uppermost portion of the magma chamber is forcefully ejected by the escaping gases the confining pressure on the molten rock directly below drops suddenly. Rather than a single bang volcanic eruptions are really a series of explosions. Following explosive eruptions, degassed lava may slowly move out of the vent

intrusions

aka plutons. Structures that result from the emplacement of magma into preexisting rocks. Form far below earths surface, they are studied primarily after uplifting and erosion have exposed them. Challenge lies in reconstructing the events that generated these structures millions of years ago and in vastly different conditions deep underground. Occur in a great variety of sizes and shapes. Intrusive igneous bodies are generally classified according to their shape as either tabular or massive and by their orientation with respect to the host rock. Igneous bodies are said to be discordant if they cut across existing structures and concordant if they inject parallel to features such as sedimentary strata

joints

allow water to penetrate to depth and start weathering process more quickly

sills

another type of tabular intrusive body. Nearly horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds or other structures. Tend to accumulate magma and increase in thickness. Typically shallow features, occurring where the country rocks are sufficiently brittle to fracture. Dykes and sales are relatively uniform in thickness , assumed to be the product of very fluid and therefore mobile madness. Closely resemble buried lava flows. Palisades sill forms an imposing cliff that can be easily seen from the opposite side of the Hudson. Generally form in near surface environments and maybe only a few meters thick, the emplacement often cools quickly enough to generate a fine-grained texture

frost wedging

as Water Works its way into the cracks in a rock the freezing water enlarges the cracks and angular fragments are eventually produced; In Frost heave,. lenses of ice grow larger as they attract liquid water from surrounding pores. the growth of these ice masses gradually weakens The Rock causing it to fracture

temp. affecting viscosity

as lava cools, viscosity increases

categories of pyroclastic material

ash, lapilli, blocks, bombs, scoria, pumice

large igneous provinces

basalt plateaus; Voluminous accumulations , extruded along fissures in a relatively short time. Most have a basaltic composition and tend to be flat and broad. Example is the Columbia Plateau

stoping

blocks of the roof overlying a hot rising mass become dislodged and sink through the magma. Further upward movement of a magma body may be accomplished by this process

lapilli

cinders; pyroclastic material;

pyroclastic flows

nuée ardentes; Hot gases infused with incandescent ash and larger lava fragments. Capable of racing down steep volcanic slopes at speeds that connects seed 100 kilometers per hour. Composed of two parts, low density cloud of hot expanding gases containing fine ash particles and a ground-hugging in portions often composed of pumice and other vesicular pyroclastic material. Propelled by force of gravity , tend to move in a manner similar to snow avalanches.

decompression melting

occurs where hot solid mantle rock ascends in zones of convective upwelling, thereby moving into regions of lower pressure. This process is responsible for generating magma along divergent plate boundaries where plates are drifting apart. Below the Ridgecrest, hot mantle rock rises and mounts, replacing the material that shifted horizontally away from the ridge taxes. Also occurs when a sending mantle plumes reach the uppermost mantle

intraplate volcanism

occurs where there is a mantle plume. in the middle of a tectonic plate

laccoliths

sheet intrusion (or concordant pluton) that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base. Igneous rock forcibly injected between sedimentary strata, so as to arch the beds above while leaving those below relatively flat. Examples in Utah

composite volcanoes

stratovolcanoes; Most are located in a relatively narrow zone that rims the Pacific Ocean , Ring of Fire. This active zone consists of a chain of continental volcanoes. Potentially dangerous. Large and nearly symmetrical , consisting of alternating layers of explosively erupted cinders and ash interbedded with lava flows. Reflect the viscous nature of the material from which they are made. Product of silica-rich magma that has an andesitic composition. However many also emit various amounts of fluid basaltic lava and occasionally material with a rhyolitic composition. Conical shape , Steve summit area and more gradually sloping flanks. Core fragments ejected from the summit crater tend to accumulate near their source and contribute to the steep slope. Find a ejected materials are deposited as a thin layer over a large area that acts to flatten the flank of the cone.

pyroclastic materials

tephra; pulverized rock and lava fragments ejected from vent