Envioronmental Geology

Concept of time in geology: principle of uniformitarianism: the landscapes we see today developed over a long period of time through the work on many slow geologic processes that still oprate today

Potentially hazardous geologic processes include plate tectonic processes such as earthquakes and volcanism weathering and erosion: processes that cause landslides, subsidence, and flooding; and climate change

Resources include energy resources. minerals and ores, building materials, soils and fertilizers for agriculture, and last but not least the clean air and water needed to support life.

those which cannot be replenished by geoloic processes within our lifetimes. This includes fossil fuels such as oil and coal and nearly all types of mineral resources.

• Earth may be the only planetary body in the solar system with active plate tectonics
• Earth is also the only planetary body in our solar sysatem where large quantities of water exist in all three phases: Liquid vapor and ice

concept of time ingeology is embodied in the principle of uniformitarianism: the landscapes we see today developed over a long period of time through the work of many slow geologic processes that still operate today

• Potentially hazardous geologic processes inclufe plate tectonic processes such as earthquakes and volcanism; weathering and erosion: processes that cause landslides , subsidence, and flooding; and climate change
• resources inculde energy resources, mineral, adn ores, building materials, soild and fertilizers for agriculture, and las tbut not least the clean air and water needed to support life

planets grew from the impact of innumerable smaller bodies early in the hisotry of the solar system

Once in a molten state, the Earth segregated into layers of different composition on the basis of density *differentiation*

crust is the thin outer shell composed of light Oxygen(O), Silicon (Si), and aluminum (Al). The crust is from 10 to 70 km thick (5 to 30 miles)

mantle has an intermediate composition, mostly magnesium(Mg), iron(Fe), and silicon(Si). The mantle is 2,900 km (2000 miles) thick

is the innermost densest layer composed of heavier elements, namely iron(Fe), and nickel (Ni). The center of Earth is 6,300 km (4,000 miles) below the surface

• is the cold, rigid outer region consisting of the crust and uppermost mantle where materials are well below the melting point temperature
• variable: up to ~70 km thick beneath ocean basins but thicker beneath continents and especially beneath mountain ranges.

plastic region of the upper mantle where rocks are weak and easily deformed because they are close to their melting point (up to 670 km depth)

deep part of the mantle where rocks are again rigid despite their high temperature due to high confining pressure (670-2890 km depth)

solid iron (>5140 km depth)

liquid iron (2890-5140 km depth)

is less dense and thicker, with a chemical composition similar to the rock type granite (made of the elements Si, O, Al, K, Na)

is more dense and thinner, with a chemical composition similar to the rock type basalt (made of the elements Si, O, Al, Ca, Mg, Fe)

the process where hot material, heated from below, rises and is replaced by the sinking of cold material. Convection currents in the asthenosphere drag the rigid lithosphere along for the ride

underlying asthenosphere is weak and deforms readily, tectonic plates have the ability to rise and sink. This property is called isostasy and occurs because the crust floats on top of the mantle like icebergs in water.

Compressional (P) waves generate a back-and-forth motion parallel to the direction of travel. P-waves can propagate in both solids and liquids

shear(S) waves move up-and-down perpendicular to the direction of wave transmission. S-waves can propagate in solids but no liquids

• Planets grew from the impact of innumerable smaller bodies early in the history of the solar system. This process is called planetary accretion
• once in a molten state, the Earth segregated into layers of different composition on the basis of density this process is called differentiation

• crust is the thin outer shell composed of light elements like oxygen (O), silicon (Si), and aluminum (Al). The crust is from 10 to 70km thick (5 to 30 miles)
• The mantel has an intermediate composition mostly magnesium(Mg), iron(Fe), and silicon (Si). The mantle is 2,900 km (2000 miles) thick.

• Earth's magnetic and gravitational fields, and the study of earthquake seismic waves.
• The answer was deduced from several lines of indirect evidence

the way researcher work collectively over time to develop an accurate, reliable, and unbiased explanation of the world around us. This is accomplished by repeated observation, testing, and modification.

attempt to explain the observations

is a hypothesis that has withstood repeated scrutiny over time

Alfred Wegener proposed the hypothesis of continental drift in 1915. Wegner's hypothesis attempted to explain the jig-saw fit between continents on either side of the Atlantic Ocean. Wegner stated that the continents were once joined as one land mass he called pangaea

meaning "all lands" in greek when all the continents were one

• resembles that of a simple bar magnetic with two poles of opposite polarity because the magnetic field is generated by Earth's rotation, the magnetic poles are within a few degrees of the rotational poles.
• Magnetic fields are produced by the motion of electrical charges

resembles that of a simple bar magnetic with two poles of opposite polarity

is the angle (dip) of the magnetic field lines with respect to the surface of the Earth and varies from 0 degrees (horizontal) at the magnetic equator to 90 degrees (vertical) at the magnetic poles.

when magnetic field reverses direction

(magnetic north pole near the geographic North Pole) are said to have normal polarity

(magnetic north pole near the geographic South Pole) have reversed polarity

When the magnetic polarity and inclination of rocks of different ages from the same continent are plotted on the map, they appear to indicate that the magnetic poles have wandered great distances over time. Rocks from different continents appear to show the magnetic poles taking different paths at the same time. This phenomenon is known as apparent polar wander.

magnetic pole does move, it remains withing a few degrees of the geographic pole because the magnetic field is generated by the earth's rotation. This is known as true polar wander.

The topography of the seafloor was found to be dominated by huge underwater mountain ranges called mid-ocean ridges

ocean basins is the narrow but very deep trenches

The orgin of earthquakes becomes deeper along one side of the ocean trenches with increasing distance from the trench. This marks the descent of old oceanic crust into the mantle as it is destroyed. This process is known as subduction and the places where it occurs are called subduction zones. Throughnthe process of subduction, old, cold, and dense oceanic crust is recycled back into the mantle.

observations of continental drift, seafloor spreading, and subduction together while also explaining related geologic phenomena (such as volcanoes and earthquakes).

The earth's lithosphere is broken into about a dozen major pieces and numerous smaller fragments called plates.

• The scientific method consists of the following steps:
• 1. Observe: gather information about some phenomenon through observation, sampling, data collection, and experimentation.
• 2. Hypothesize: attempt to explain the observations
• 3. Predict: use the hypothesis to make testable predictions
• 4. Test: gather additional evidence from observations or experiments that may support or refute the hypothesis.
• 5. Modify: modify the hypothesis in light of new evidence. Steps 3-5 are repeated until a hypothesis has been developed that is consistent with all available evidence and conceivable tests.

• Continents were once joined also distribution of fossils across the southern continents. The same fossils of land animals (early reptiles) and plants (such as seed ferns) are found on continents that today are separated by vast oceans.
• The ages and types of rocks on all the coasts were similar and when they were pieces back together they lined up nicely

• Divergent plate boundaries occur where plates are being pulled apart.
• New oceanic crust is created
• associated with extensional stress, shallow earthquakes,and basaltic volcanism. Examples include the mid-ocean ridges such as the Mid-Atlantic Ridge.

The molten iron in the Earth's outer core combine with the Earth's rotation generates a magnetic field. Molten iron in the outer core flows around the solid inner core because of Earth's rotation. The flow generates an electrical current, in turn creating a magnetic field. Earth's magnetic field resembles that of a simple bar magnetic with two poles of opposite polatiry.

• a continent is being pulled apart a new divergent boundary continental rift valley East African Rift Valley is an examplerepresent
• the earliest stage in the development of a new ocean basin as a
• singlecontinental plate splits into two fragments as new oceanic crust
• grows between them.

• Transform plate boundaries occur where two plates are sliding past each other in differentdirections.
• occurs where two plates are sliding past each other in different directions. The boundary is marked by a system of
• faults.
• resulting in earthquakes

• rising magmaproduces a chain of volcanoes on the overriding, younger oceanic plate called a volcanic islandarc.
• volcanic arc is built on the overridingcontinental plate as the subducted oceanic plate melts.

have a magma source in the deep mantle, perhaps extending all the way to the core boundary.

produced as the plate moves over the stationary hot spot.

very ancient rock that makes up the cores of continents

belts of deformed rocks representingmountain building episodes during collisions between continental cratons.

Continental shields are assemblages of ancient cratons and their associated orogens suturedtogether by tectonic collisions.

building continents, plate motions also tear continents apart.

• continental rift develops into a new ocean basin, the edges of the continent
• transition between oceanic andcontinental crust that does not coincide with an active plate boundary.
• is at the mid-ocean ridge.

Underlain by older oceanic crust that has movedaway from the ridge, cooled, and subsided, and covered by a veneer of marine sediment.

abyssal plains end abruptly at the continental slope where the crust transitio ns to lighter and more buoyant continental crust.

continental shelf is the low- lying portion of the continent flooded by shallow seas.

Eventually, a passive continental margin develops into a new subduction zone as the adjacentoceanic crust becomes older, colder, and denser. The ocean basin, while still spreading at themid-ocean ridge, starts to grow smaller as oceanic crust is subducted. As the intervening oceanbasin disappears the continents are drawn into a new round of collision, albeit in a new place.This cycle of continent formation, breakup, and re-assembly is called the Wilson Cycle.

Active continental margins are found where subduction occurs between an oceanic and acontinental plate. Active continental margins coincide with plate boundaries.

• When two continents collide, neither is subducted. Instead, the compressional stress producesthickening and thrust faulting, which uplifts mountain ranges and high plateaus along andbehind the collision zone.
• crust is heated by rising magma from the mantle
• causing uplift of a broad area.
• rising magma continues to pushthe crust aside, the uplift collapses to form a rift valley (2). New oceanic crust is created as therift spreads. The area is flooded to form a narrow sea such as the Red Sea (3). The narrow seamay grow to become a new ocean basin with a mid-ocean ridge and seafloor spreading center(4). Rifting can end at any point, not all rifts develop into a new ocean basin.

• The tectonic setting of the Pacific Northwest is an active plate boundary where small oceanicplates, the Gorda (south), Juan de Fuca (central), and Explorer (north) plates are colliding withand being subducted by the continental North American Plate.
• inland, a volcanic arc, the Cascade Range, is formed on theoverriding plate above the depth where the subducted oceanic plates begin to melt and producemagma, which rises to the surface. The coastal and Cascade ranges are separated by a fore-arcbasin, a topographic depression produced by down-warping of the continental plate like a rugdue to the tremendous stresses from the subduction zone. This depression is occupied by PugetSound and the Williamette Valley.

Magma is a liquid with a silicate composition (50-90% Si-Al-O). Magma may also containgases, either dissolved or exsolved (bubbles); and solids such as minerals crystallizing from theliquid or unmelted residual rock.

magma that erupts on teh surfave is called lava.

melting point is a function of both temperature andpressure, lowering the pressure also lowers the temperature at which melting occurs. This is called decompression melting and occurs when mantle material migrates upwards to areas of lower pressure

Basaltic magma has a relatively low silica content (45 -55%), is high in Fe, Mg, and Ca,and low in Na and K. This composition is said to be mafic and is enriched in chemical elements that form dark-colored minerals.

magma has an intermediate silica content (55-65%)and intermediate amounts of Fe, Mg, Ca, Na, and K. This composition is said to be intermediateand contains more equal amounts light and dark colored minerals.

Rhyolitic magma has a high f)silica content (65-75%), is high in Na and K, and low in Fe, Mg, and Ca. This composition issaid to be felsic and is enriched in the chemical elements that form light-colored minerals.

• Changing the amount of melting (partial melting) also produces different compositions of magma, even from the same parent material.
• Magmas of different compositions can be generated from the same parent material by differentamounts of partial melting.

crystallizing minerals are separated from the residual magma during cooling

Bowen’s Reaction Series is the sequence of minerals that form from a cooling magma.

The initial melt is therefore also high insilica (felsic).

As temperature increases and melting continues, moremafic minerals start to melt, such as biotite, amphibole,and pyroxene. This makes the melt progressively moremafic.

Contamination occurs as rising magma assimilates surrounding rock. Heat from the risingmagma also melts the surrounding rock, creating a second magma.

The two magmas may mix (magma mixing) to produce a new composition.

Viscosity describes a magma’s resistance to o)flow and is determined by silica content (composition) and temperature. Viscosity increases withincreasing silica content but decreases with increasing temperature.

a low viscosity, high temperature pahoehoe flow.

high viscosity, low temperature aa flow.

Higher temperature, lower viscosity magmas tend to have lower gas contents andproduce gentler, effusive eruptions.

Lo wer temperature, higher viscosity magmas tend to havehigher gas contents and produce violent, explosive eruptions.

The continuous branch of Bowen’s reaction series describes the evolution of the plagioclasefeldspars from calcium- rich to sodium rich. Early formed minerals react continuously with themelt to form new minerals with the same structure, but different chemistries.

• (partial melting) (fractional crystallization)
• contamination of magma by melting andincorporating new material. We can also mix magmas formed from different parent materials to get a new magma composition.

• The magma is fountaining but noash or pyroclastic material is being produced. Instead the magma runs away from the vent as athin, fluid, lava flow.
• Explosive eruption of high viscosity magma in Sicily produced pyroclastic material as moltenrock is erupted explosively through the air to form ash, scoria, and bombs. Once the magma hasdegassed the style of eruption will change to effusive production of a thick, blocky lava flow.

Felsic (rhyolitic) igneous rocks are produced by melting of continental crust and so felsicigneous rocks consist of mostly light colored minerals rich in silica, K, and Na, and are poor inFe, Mg, and Ca. Felsic igneous rocks include granite and rhyolite.

igneous rocks contain a more equal mixture of light and dark minerals and include andesite and diorite

Mafic (basaltic) igneous rocks are produced by melting of the Earth’s mantle and consistof mostly darker minerals rich in Fe, Mg, and Ca, and poor in K, Na, and silica.

Composition refers the types and relative abundances of minerals present, which depends onthe composition of the magma from which the rock was crystallized.

Texture refers to the size, shape, and arrangement of minerals present. The texture of igneousrocks depends on how crystallization occurred.

• Intrusive igneous rocks: Crystallized slowly from cooling of magma beneath the Earthsurface, allowing large crystals time to form.
• Intrusive rocks are coarse-grained.

• Extrusive igneous rocks: Crystallized quickly from cooling of lava erupted at the surface,crystals are generally small.
• Extrusive rocks are fine-grained.

Coarse-grained, intrusive igneous rock texture with large crystals easily seen by the naked eye iscalled phaneritic.

Fine- grained, extrusive igneous rock texture with small crystals that may be difficult to seewithout magnification is called aphanitic.

Porphyritic texture is mostly fine grained matrix with embedded larger crystals, indicating partialcrystallization underground followed by eruption onto surface.

isolated large grains are phenocrysts.

Igneous rocks with a vesicular texture have void spaces (bubbles) left by escaping gas.

Pyroclastic rocks from when molten material is erupted explosively through the air and cools asit falls.

If the ash was still hot when it fell back to thesurface, it may weld together to form a type of rock called tuff.

Rocks such as obsidian or volcanic glass are glassy with no crystal structure, and are formed byvery rapid cooling on the surface. There is no crystal structure because atoms lack time toorganize themselves into minerals. Such rocks are said to have vitreous texture.

• A felsic (also called rhyolitic or granitic) igneous rock is composed mostly of light coloredminerals and is called granite if it is intrusive
• Granitic rocks are found in the continental crust. Granitic magma forms when continental crust is heated to its melting point.

Diorite is composed mostly of plagioclase feldspar, with significant amounts of amphiboles andpyroxenes.

Dark-colored diorite grades into gabbro. Gabbro is composed mostly of mafic minerals such aspyroxene, amphiboles, and olivine.

A coarse-grained igneous rock in which olivine is the most abundant, and sometimes the only,mineral present is called peridotite. Peridotite is abundant in the mantle but exposures at thesurface are relatively rare.

Rhyolite has the composition of granite but is an extrusive (or volcanic) rock. The same mineralspresent in granite are also found in rhyolite but the crystal sizes are very small.

Andesite is a quartz-poor intermediate igneous rock, the intrusive equivalent is diorite.

Basalt is the extrusive equivalent of gabbro. Basalt is the most common kind ofextrusive igneous rock and makes up most of the oceanic crust.

Extrusive igneous rocks that are largely or wholly glassy are called obsidian.

pumice consist of y)very light pyroclastic materials erupted through the air. Pumice is typically both light in color,due to a felsic composition; and light in density, because of the large amount of void space due to escaping volcanic gases

Rocks that cool slowly underground have large mineral crystals, phaneritic texture, and are saidto be intrusive. Rocks that cool quickly by eruption at the surface have small mineral crystals,aphanitic texture, and are said to be extrusive.

• Magma that solidifies on the surface usually cools rapidly, allowinginsufficient time for large crystals to grow.
• Extrusive and intrusive igneous rocks are easily distinguished by texture.

Basaltic magmas produce gently sloping shieldvolcanoes if the magma is gas poor or cinder cones if the magma is initially gas rich. Shield volcanoes are gently sloping and broad volcanoes built up over time by successive thinand fluid lava flows. Eruptions of shield volcanoes are gentle and effusive eruptions of fluidbasaltic lava. Shield volcanoes are found at oceanic hot spots

eruption that taps the gas-rich magma at the top of the chamber is characterized by frothyejection of material into the air, pyroclastic (hot rock) fragments accumulating around anddownwind from the vent. Numerous gas bubbles "frozen" into place because they cooled too quickly for crystals to becomelarge enough to see.

• Andesitic magmas produce tall, conical stratovolanoes (also called composite volcanoes).
• characterized by steep sides and conical shapes and are onlyfound at subduction zones because they erupt andesitic magma produce by partial melting of subducted oceanic crust.
• periods of explosive activity triggered byaccumulated, pressurized gases followed by quieter effusion of intermediate viscosity andesitic lava flows as the magma degasses.
• lava flows and pyroclastic deposits,

• Andesitic magmas produce tall, conical stratovolanoes (also called composite volcanoes). characterized
• by steep sides and conical shapes and are onlyfound at subduction zones
• because they erupt andesitic magma produce by partial melting of
• subducted oceanic crust.periods of explosive activity triggered
• byaccumulated, pressurized gases followed by quieter effusion of
• intermediate viscosity andesitic lava flows as the magma degasses.lava flows and pyroclastic deposits,

• Lava domes consist of high viscosity rhyolitic magma.
• eruptions of rhyolitic volcanic domes are mostly explosive and build a steep sideddome that is prone to collapse.

Extrusion of a small rhyolitic lava dome often ends an eruption sequence at a stratovolcano, allowing pressure to build up by plugging the volcano’s vent until itis cleared by the next explosive eruption.

mountains built by eruptions around a localizedarea or vent, often many different eruptions over thousands of years.

Eruptions may also takeplace along elongated cracks called fissures or rifts where weaknesses in the crust provide a path for molten rock to reach the surface. Fissures can form locally on the flanks of a volcano or affect large regions where divergent stresses are rifting the crust.

Regional fissure systems can feed voluminous outpourings of basalts called flood basalts, whichcover large areas of the ocean floor. Flood basalts can also be found on the continents. TheColumbia Plateau of eastern Washington and Oregon is an example of a continental flood basalt

Calderas are large circular depressions produced by the rapid, eruption of a large volume of magma. This leaves the volcano unsupported, resulting in its collapse into the drained magma chamber.

Pyroclastic flows are high-density mixtures of hot, dry rock fragments and hot gases that moveaway from the vent that erupted them at high speeds. Most pyroclastic flows consist of two parts:a basal flow of coarse fragments that moves along the ground, and a turbulent cloud of ash thatrises above the basal flow. The explosive eruption of Mount St. Helens on July 22, 1980, shows the development of apyroclastic flow.

Tephra is a general term for fragments of volcanic rock and lava regardless of size that areblasted into the air by explosions or carried upward by hot gases in eruption columns or lavafountains. Such fragments range in size from less than 2 mm (ash) to more than 1 m in diameter.

• A massive lahar could occur at any time if part of the volcano collapses. An eruption could melt the mountain’s ice cap and trigger a series of lahars. Hundreds of thousands now live in path offuture lahars from Mount Rainier.
• Composite volcanoes are characterized by a mix of explosive and effusive activity. hazards include pyroclastic flows, ashfall, and lahars.

A lahar is a mixture of water and rock fragments flowing down the slopes of a volcano andchanneled a great distance from the volcano along river valleys. Lahars are sometimes referredto as volcanic mudflows or debris flows.

phreatic (steam) explosions produced as hot rock came into contact with groundwater

• Suddenly depressurized, hot magmatic gases and compressed air from debris avalanche created alateral directed blast that affected the area north of the volcano.
• the lateral blast hazard from flank collapse wasunfortunately not recognized. The main visitor center at Mount St. Helens is named for Johnston,who died in the eruption and was never found.

faults: surfaces marking the movement of rock in different directions.Faults can move in both horizontal and vertical directions.

force exerted per unit area within rocks or other Earth materials.

a result of stress the rocks along the fault experience strain or deformation such a a change in their size, shape, or g)orientation.

amount of strain along the fault exceeds the strength of the rocks, the rocks rupture or break, causing sudden movement and release of the stored strain energy as seismic waves.

The elastic rebound theory describes how earthquakes are generated by accumulated strain alonga fault. Strain builds up in rocks due to movement along fault, causing deformation of the rocks.Once the accumulated strain exceeds strength of the rocks, the rocks break and the fault ruptures,producing an earthquake.

Primary waves (P-waves) travel the fastest, so they arrive at the recording station first P-waves produce alternating compression and relaxationparallel to the direction of wave propagation, and can travel through both solids and liquids.

shear waves (S-waves) produce up-and-down motion perpendicular to the directionof wave propagation. S-waves travel slower than P-waves, but faster than surface waves, so theyarrive second (hence the name secondary waves). S-waves only propagate through solid materials

Richter magnitude of an earthquake is determined from the maximum amplitude of groundmotion as recorded by seismic waves registering on a seismograph along with the distance to theepicenter (also determined from the seismograph).

• geologic record for such information in #8order to make predictions about the frequency of earthquakes on the CSZ. Because the coastlineof Washington and Oregon experiences abrupt subsidence during a CSZ earthquake (due torelaxation of the tectonic plate), marshes and beaches in the PNW are a great place to get data onpast CSZ earthquakes. Coastal subsidence drops low- lying forests into the intertidal zone where they are killed by saltwater.
• Counting the number of turbidites between dated sedimentlayers gives the average frequency of earthquakes on the subduction zone.

Normally fined-grained marine sediments are punctuated by layers of coarser material depositedby underwater debris flows (turbidites) caused by shaking of loose sediments on underwaterescarpments.

is a complex mixture of weathered mineral matter, dead organic matter, gases, and water

• initial product of rock weathering is broken down mineral
• is not capable of supporting plant growth because it does not contain plant essential nutrients such as nitrogen which is rare in rocks

decomposed plant and animal material

is the breakdown of rock over time into smaller fragments and into new chemical compounds by both physical and chemical processes.

Erosion is the removal and transport of weathered material by water, ice or wind.

Eroded material is eventually deposited elsewhere as sediment

also called mechanical weathering, is the breaking of rocks into smaller fragments with no change in their chemical composition.

• the principal agent of physical weathering
• The freezing of water which seeps into any cracks or fractures, expanding when it freezes and wedging and wedging the rock apart.

intrusive igneous rocks such as granite that cooled far underground, fracture when they are exposed to lower surface pressures by uplift and erosion of overlying rock

The decomposition of rocks and minerals into new forms by chemical reactions involving water or oxygen, such as carbonate dissolution, oxidation, hydrolysis, and hydration

reactions rocks such as limestone are dissolved by carbonic acid, a weak acid formed by dissolving atmospheric carbon dioxide into rainwater:

A weak acid formed by dissolving atmospheric carbon dioxide into rainwater

the reaction that occurs with oxygen. Iron and aluminum oxides are the most common oxides. These oxides produce red and yellow staining of soils.

• the addition of water
• silicate minerals such as micas and feldspars results in clay minerals

• reaction with water that decomposes silicate minerals
• Mg₂SiO₄+4H₂O->2Mg²⁺+4OH^-+H₄SiO₄

Soild that form in0situ by weathering of bedrock

soils that develop on sediment transported from elsewhere

sediment transported by wind

excellent texture, fertility, and water-holding properties, underlie many of the world's most productive agricultural regions.

• O- mostly organic materials, decomposing leaves, and twigs. Often dark brown in color.
• A- topsoil consisting of a mixture of organic and mineral matter. Horizon A is the Zone of Leaching where clay, Ca, Mg, fe, and carbonate are removed to lower horizons
• B- Enriched in clay, Fe oxides, Silica, carbonate and other material leached from above. The B horizon is also known as the Zone of Accumulation
• C- Partially altered (weathered) parent material, which is either rock or loose sediment
• R- Unweathered (unaltered) parent material(bedrock)

where clay, Ca, Mg, Fe, and carbonate are removed to lower horizons

The B horizon

a list of the horizons that describe a particular soil. A soil's profile depends on its age and its conditions of formation

soil taxonomy is the terminology used by soil scientists for calssification of soils based on their profile

texture according to the proportion of clay, silt, and sand sized-paticles

One particle size

multiple particle

results from the tendency of soil particles to clump together in characteristic shapes such as granular, platy, blocky, or prismatic

refers to the ability of a soil to deliver the nutrients essential for plant growth

removes soild particles in more or less even layers.

is the carving or gullies or streamlets by running water and is more common on steeply sloping land. Rills can develop on gently sloping land, however, where running water is concentrated

• is the transformation of a semi-arid landscape into a more deser-like environment because of human misuse.
• The lowering of the regional water table through groundwater pumping and irrigation and the loss of stabilizing vegetation cover due to agricultural uses such as grazing and crop cultivation

othe 1930's that struck the US Great Plains was an example of desertfication cause by poor agricultural practices

• the perennially frozen soils found at high altitudes and high latitudes.
• Structures not properly designed for permafrost conditions can warm and thaw the underlying permafrost, leaving a soupy much invapable of supporting structures.

• the decomposition of rocks and minerals into new forms by chemical reactions involivng water or oxygen, such as carbonate dissolution, oxidation, hydrolysis, and hydration. in carbonate dissolution reactions, rocks such as limestone are dissolved by carbonic acid, a weak acid formed by dissolving atmospheric carbon dioxide into rainwater
• breaking of rocks into smaller fragments with no change in their chemical composition

breaking rock into smaller fragments, promotes chemical weathering by increasing the available surfave area for attack by chemival weathering

• O- mostly organic materials, decomposing leaves, and twigs. Often dark brown in color.A-
• topsoil consisting of a mixture of organic and mineral matter. Horizon
• A is the Zone of Leaching where clay, Ca, Mg, fe, and carbonate are
• removed to lower horizonsB- Enriched in clay, Fe oxides, Silica,
• carbonate and other material leached from above. The B horizon is also
• known as the Zone of AccumulationC- Partially altered (weathered) parent material, which is either rock or loose sedimentR- Unweathered (unaltered) parent material(bedrock)

• essential roles as substrates for food, fiber (ie cotton), and wood production, in the recycling of carbon and other nutrients, in water storage and filtration, and a source of building materials, foundations for structures, and caps for landfills.
• Soils are a fragile resource that can take thousands of years to form and are easily lost to erosion or degraded

• Soil erosion is the loss of soil to wind or water and is caused by removal of natural vegetation, poor agricultural processes, overgrazing, and any other process that strips soil of protective vegetation cover or increases exposure to surface water runoff.
• Rill erosion is the carving or gullies or streamlets by running water and is more common on steeply sloping land. Rills can develop on gently sloping land, however, where running water is concentrated.
• Strip cropping alternates closely spaced crops with widely spaced ones, which helps trap soils washed from bare areas. Crop rotation involves alternation row crops such as corn vulnerable to soil loss with soil enriching crops such as grasses and alfalfa. conservation tillage are practives such as minimizing plowing in the fall, retaining the stubble of previous year's crops, and contour plowing parallel ro the hill-slope so that furrows will catch runoff. no-till and minimal till are practives that minimize mechanical disturbance of the soil by planting seed with stubble still in place or using chamicals instead of plowing to control weeds.

caused by soil salinization due to evaporation of irrigation water.

Foliated metamorphic rocks are classified by texture and grade. Increasing metamorphism of aclastic sedimentary rock such as shale produces:

Non-foliated metamorphic rocks are classified by composition.

Sedimentary rocks consist of a)weathering products eroded, transported, and re-deposited as sediment.

Metamorphic rocks form by re-crystallization of pre-existing rocks at high temperatures and pressures but without melting.

rock cycle links the different geologic materials (magma, sediments) and types of rocks(igneous, sedimentary, metamorphic) by the ir processes of formation. The rock cyclecontinuously recycles earth materials to make new rocks from older rocks with no starting orending point.

melting of rocks to producemagma, the cooling and crystallization to magma to produce igneous rocks, the weathering ofigneous, sedimentary, or metamorphic rocks to produce sediment, the lithification of sediment bycompaction and cementation to produce sedimentary rocks, and the metamorphism of igneous,sedimentary, or metamorphic rocks to produce metamorphic rocks.

sedimentary rocks involves the weathering of existing rocks by physical andchemical weathering processes to produce sediment, as discussed in an earlier lecture. Sedimentis transported by water, wind, or ice before being deposited. Finally, the processes of lithificationturn sediment into sedimentary rock by burial, compaction, and cementation.

Clastic sediment is solid, weathered mineral grains, loosefragments of rock debris produced by physical weathering. Examples include sand, gravel, and clay

provenance of clastic sediment refers to the parent material from which the sedimentwas derived (granite, basalt, etc.) as indicated by the types of minerals present.

Chemical sediment is the water-soluble products of chemical weathering carried as dissolved ions inchemical solution. Chemical sediment is analogous to sugar cubes dissolved in tea. Examples include calcium carbonate and salt.

Biogenic sediment consists of the dead remains of plants and animals. Examples include coal and organic-rich mud.

Lithification is the transformation of loose sediment to sedimentary rock by compaction and cementation

Shale is composed of very fine,clay-size particles. Individual particles are too small to see with the naked eye, but shows finely laminate bedding planes.

Siltstone contains fine, silt-size particles barely visible with the naked eye

Sandstone is made of coarse, sand-size particles easily visible with the naked eye.

Conglomerate consists of very coarse, gravel and larger sizes, particles may be rounded orangular (in which case the rock is called breccia).

Limestone is calciumcarbonate (may also be biogenic). Limestone is easily distinguished by reaction with acids such as HCl.

Evaporite is composed of salts such as halite (NaCl) or gypsum (CaSO4 ). Evaporites are most easily distinguished fromother chemical sedimentary rocks by their salty taste.

Metamorphism is the changes in mineral types and texture that occur when a rock is subjected toconditions different from those under which it originally formed.

Metamorphism occurs when rocks are buried deep within the #3Earth by tectonic collision, subjected to high pressures by subduction, or when intruding magmabakes surrounding rock. Metamorphism results in recrystallization of minerals that are unstableunder the new conditions to more stable minerals but without melting.

High pressure is often applied directionally, resultingin a preferred orientation of platy or elongate mineral grains called foliation.

Burialmetamorphism occurs in deep sedimentary basins such as passive continental margins. Burialmetamorphism occurs at modest increases of pressure and temperature under a normal geothermal gradient and is aided by chemically active fluids.

Contact metamorphism occurs when bodies of hot magma intrude into cool rocks of the crust,subjecting the surrounding rocks to high temperatures and low pressures (a high geothermalgradient).

Regional metamorphism results from tectonic forces that build mountains and is characterized bydirectional pressure and extensive mechanical deformation. Regional metamorphism results infoliated rocks with a preferred orientation of platy minerals because the pressure is applieddirectionally during a tectonic collision.

Regional metamorphism affects large regions duringmountain-building tectonic collisions called orogenic belts that allow us to track the assembly of the continents over time.

Microscopic	Quartz, chlorite muscovite	Subtle, slatey cleavage	slate
Barely visible	Quartz, muscovite, kyanite	fine grained schistosity	Phyllite
Large and easy to see	Quartz, muscovite, biotite, garnet, sillimanite	Coarse grained schistosity	Schist
Large and easy to see	Quartz, muscovite, biotite, garnet, sillimanite	Coarse grained schistosity	Schist

Cross-bedding is inclined planes within a bed. Cross-bedding is a result of turbulent flow instreams, wind, or ocean waves creates cross-bedding.

Superposition states that sedimentary rock layers are deposited in order from the bottom (oldest)to the top (youngest).

Cross-cutting relationships allow us to place episodes of igneous intrusion,folding, and faulting in the correct chronological order within a sequence of rock units.

Unconformities are gaps in the stratigraphic record representing periods of time in whichsedime nts were either not deposited or have been eroded.

nonconformity occurs when sedimentary strata directly overly igneous or metamorphic rocks.

Relative ages place rock units and geologic events in chronological order using the principles ofstratigraphic superposition, correlation, and cross-cutting relationships.

Absolute ages are numerical ages in years determined using the principles of radioactive decay.

eon is the largest interval into which geologic time is divided. There are four eons: theHadean Eon, Archean Eon, Proterozoic Eon, and Phanerozoic Eon.

The Phanerozoiceon is subdivided into shorter time units called eras: the Paleozoic Era (meaning early life)

• The eras are further subdivided into periods on the basis of the fossil record.
• In turn, periods are divided into epochs.

Epochs are the shortest subunit of geologic time but still span millions of years.

The shape of a slope is its profile.

Slopes formed in arid climates or from rocks resistant to weathering and erosion typicallyhave a near-vertical free face.

base of the free- face is a pile of loose rock debris known as a talus slope accumulated from many years of mass-wasting events.

Types of mass wasting include landslides, slumps, soil creep, debrisflows, rockfall, and other forms of slope and ground failure.

Translational slides move on a planar surface, while rotational slides (also called slumps) moved on a curved (concave) surface.

Creep is a very slow flow involving alternating expansion and contraction of the slopematerial. This could be by periodic wetting and drying or freezing and thawing of a slope.

Debris avalanches: very rapid debris flows

• initiating slope failure by increasing the driving forces and decreasing the resisting forces.
• Vegetation adds weight to a slope, increasing the driving forces. Roots add cohesion toslope, increasing the resisting forces. Vegetation cover can increase the water content of aslope by slowing runoff, allowing more water to infiltrate a slope. This increases thedriving forces. Vegetation could also decrease the water content of the slope as water isremoved from the soil via uptake by roots and transpiration from leaves. This wouldreduce the driving forces.

• Causes include loading the top of a slope, removing support from the base of aslope, increasing the gradient of a slope, changing the vegetation cover, and altering thewater content and drainage patterns.
• 1. Artificial excavations and fillings of loose materials during road construction altersthe mass distribution on a slope.
• 2. Any project that increases the height or steepness of a slope or places a load on it(i.e., a house) may cause slope failure.
• 3. Adding water to a slope through irrigation or concentrating runoff on part of a slopefrom culverts and ditches.

• Drainage control: reducing infiltration and diverting surface runoff using plasticsheeting, culverts, and ditches
• Slope dewatering: installation of surface and subsurface drains to remove excesswater. This reduces weight and increases shear strength of the slope.
• Slope reduction: removal of unstable material by cut-and-fill where material isremoved from the upper part of the slope and used to fill at the bottom of the slope orby benching where a series of steps are cut into the slope.
• Stabilizing structures: adding support using retaining walls at the toe of a slope, deepsupporting piles or rock bolts to anchor potentially unstable material to stablebedrock. The danger of rock fall onto roads can be minimized with chain link fencingor netting to catch falling rocks or covering a loose slope with concrete.

Isotopes are atoms with the same number of protons but a different number of neutrons.

By accepting or donating electrons, atoms become electrically charged ions. Ions are atoms with an electric charge resulting from a gain or loss of electrons

Atoms with an almost filled outermost shell accept or gain electrons and become negatively charged anions.

An anion is an atom that has gained an electron and thus has anegative charge. Atoms containing just one or two electrons in their outermost shell readilydonate or lose electrons and become positively charged cations (+).

Cations and anions are attracted to each other due to their opposite charges and form ionic bonds.

If two atoms both need an electron or electrons to fill their outermost shells, they can share anelectron and form a covalent bond. In covalent bonding atoms share electrons rather thantransferring them, creating a strong bond.

metallic bonding closely packed atoms share electrons in higher energy-level shells amongseveral atoms.

Van der Waals bonds are weak secondary attractions between certain molecules with dipoles(positively and negatively charged ends).

A mineral is a naturally occurring, inorganic solid that has a defined chemical composition andcrystalline structure.

The atoms in most solids are organized in regular, geometric patterns, called the crystalstructure.

Crystal habit is the characteristic crystal form or shape of each mineral.

Minerals that are polymorphs have the same chemical composition but a different crystallinestructure (and hence different physical properties).

Luster is the quality and intensity of light reflected from a mineral.

Cleavage is the tendency for a mineral to break in preferred directions along planar surfaces.

Silicon and oxygen are by far the most common elements in the Earth’s crust, making up morethan 70% of the continental crust by weight.

They combine to form an ion called the silicate ion(SiO 4 ) with a four-sided shape called a tetrahedron.

The carbonate anion, (CO3 )2-, forms three common minerals: calcite, aragonite, and dolomite.Calcite and aragonite are polymorphs with the same chemical composition (CaCO3 ) but differentcrystal structures. Magnesium substitutes for calcium in dolomite: CaMg(CO3 )2 .

The iron oxides, magnetite (Fe3 O4 ) and hematite (Fe2 O3 ), are the two most common oxideminerals. Iron oxide minerals are among the most important minerals economically because theyare mined as ores to recover iron, which is used to make steel.

Sulfides are the group of minerals containing sulfur. Examples include iron sulfide which is themineral pyrite (FeS2 ) and lead sulfide which is the mineral galena (PbS). Most major oresof important metals such as copper, lead, cobalt, mercury, and silver are sulfides.

The halides are a group of minerals whose principle anions are halogens. Halogens are elementsthat need one electron to have a full outer shell and so form anions with a negative one charge bygaining an electron.

The native elements are minerals composed of a single element. This includes minerals such asnative sulfur, copper, and gold.

Earth’s mineral resources can be divided into four categories based on human use: metalproduction and technology, fertilizers (agriculture), chemicals (wide variety of uses), andbuilding materials.

• Mineral resources can be made to last longer through improvedefficiency and conservation; recycling of mineral resources can make the current supply lastindefinitely.
• Mineral resources are elements, compounds, minerals, or rocks concentrated in usable formwhose extraction and use is economically viable under current market and technologicalconditions.

concentration factor is the concentration needed for a deposit to be considered an ore undercurrent market conditions divided by the average crustal abundance of that element.

Igneous processes involve the cooling and crystallization of magma (usually beneath the surface,rather than by eruption at a volcano) and include crystal settling, late magmatic segregation, and hydrothermal fluids.

Metamorphic processes involve the recrystallization of existing rocks underconditions different from those under which the rock formed, such as higher temperatures, higherpressures, or reaction with chemical rich fluids.

Contact metamorphism occurs when a host rock is intruded by a body of magma and subjected to high temperatures and/or hydrothermal fluids from the intrusion.

Regional metamorphism occurs under conditions of high pressure due to tectonic collisions between plates.

mafic magmas,heavy minerals that crystallize early in the fractional crystallization sequence settle towards the lower part of magma chamber. This is known as crystal settling

felsic magmas, late-stage magmatic processes that occur near the end of the fractionalcrystallization sequence involve the concentration of incompatible elements as ore minerals.

These metals and fluids are elements that are said to be incompatible and are notincorporated into the crystal structure of minerals commonly found in igneous rocks, whichinstead are rich in silica, aluminum, potassium, calcium, sodium, and magnesium (thoughusually not sufficiently concentrated for mining).

Hydrothermal processes occur when the late stage magmatic, metal rich fluid from an igneousintrusion crystallizes as veins either in fractures within the intrusion or in the zone of contactmetamorphism surrounding the intrusion.

pegmatites, very course grained igneous rocks with abundant largemineral crystals. Most pegmatites are granitic in composition and are mined for micas, feldspars,quartz, beryllium, lithium, and gemstones.

Kimberlites are ultramafic bodies of igneous rocksfrom the upper mantle that were intruded rapidly into the crust. Kimberlites contain diamondsscattered throughout that formed under the very high pressures of the mantle.

• strip mining, open pit mining, hydraulicmining, and dredging. The need for disposal of a large volume of mining wastes such asoverburden removed to reach the mineral deposit also results in land disturbance. Subsidenceoccurs due to collapse of pillared workings and old mine shafts, creating sinkholes. Slope failuremay also result from blasting and vibrations and increased slope angles associated with mining.
• leaching with a dilute cyanide solution used for gold mining,generates highly toxic leachate that must be treated as hazardous waste.
• major source of water pollution.