Geoscience 001 Exam 2: PSU

erosion

gradual movement of clastic materials

clastic materials

particles created by weathering processes

headward erosion

flowing water

water gap (capturing)

can form when one stream erodes through a drainage divide and intercepts another stream, thus cutting through a ridge or mountain

Drainage Divide

imaginary line that separates drainage basins and watersheds

River flows

they can reverse directions during cycles of mountain buildings

dendritic

tree-shaped branching of a river and its tributaries

radial

flow off the sides of a high point, such as a volcano into a flat plain

rectangular

flowing through rock joints at sharp angles

trellis

main river cuts through ridges with tributaries lying in valleys

resistant ridges

the ridges that the main river cuts through

rivers

most effective means of transporting sediment

load

amount of sediment carried by a rivers current; 3 ways it can be carried

3 ways Load can be carried

1. dissolved ions in water

2. clay-size particles suspended in water ("suspended load")

3. large particles moving along the stream bed (" normal bed load") - this is done through a process known as saltation

saltation

where a particle is picked up and moved, dropped to the bed, and picked up and transported again

---carrying power is highest at steep slopes---

**largest particles are carried the shortest distance

**smallest particles are carried the farthest and deposited last

competence

measure of the largest particle a stream or river is able to transport

capacity

measure of the amount of sediment able to be transported

narrow mountain streams

high competence; low capacity

wide meandering streams

low competence; high capacity

alluvial fan

stream bed carrying cobbles and boulders that are deposited in a fan shape

transport ability

calculated by

discharge = A times V ....

A = channel area

V = stream velocity

longitudinal profile

general terms used to explain the large-scale profile with respect to stream gradient when looking at a watershed of river/stream

steep gradient - further upstream

shallow gradient - further downstream

braided streams

formed when a stream beginning in steep mountains loses its carrying power when reaching a valley floor

wide meandering streams

formed because a curved channel scours the bank on the outside of a bend, causing uneven erosion and end in the river;

velocities

-greatest velocity in a straight channel is found in the center

-greatest velocity in a curved channel is found towards the outer bank of a bend (greater erosion)

oxbow lake

formed when a meandering stream cuts through curves and creates a new course while leaving a bow-shaped lake in the bend where it used to flow

meander neck

this is where the stream cuts off the old path leaving an Oxbow Lake

point bars

formed by sediment deposits along the inner bank of a curve; these are the old banks from the younger meandering stream

levees

formed along a streams bank by flooding

floodplain

flat area around a stream formed by change back and forth in a stream's course over time; during flooding the floodplain is filled with water

yazoo stream

small stream on the sides of flood plains

flash floods

results from events that lead to a rapid, often catastrophic, rise in water level; examples:

1. dam collapse

2. isolated thunderstorms in arid regions

3. ice dams created by glaciers give way

wind/air transport (sediment transport by other elements)

occurs in desert environment, must be very fine grained

loess

sediment deposited by wind

glacier transport

sediment falls down side of mountain and lands on top of glacier; fairly limited movement since the glaciers do not travel great distances

background info on sedimentary rocks

1. sedimentary rocks are formed from pre-existing rocks at the surface of the Earth

2. they form at low temps and low pressures

3. sed. rocks can incorporate sediment from igneous, metamorphic, or other sed. rocks

clastic (detrital) sedimentary rocks

formed by particles cemented together;

-classifying materials

1. mineral make-up

2. clast size

3. clast angularity

4. clast uniformity

chemical sedimentary rocks

formed by the precipitation of minerals from solution

Lithification

process in which unconsolidated particles become rock; usually occurs in the presence of water; particles put under high pressures; sediments become compacted, many pores are lost or compressed; sediments precipitate out of the solution to form cement

forming of sedimentary rocks

1. lithification

2. clastic composition reflects the depositional environment in which the rock was formed (pebble conglomerate is formed in high mountain streams; dirty sandstones are formed from sandy river deposits)

3. the most important criterion for classifying clastic sedimentary rocks (minerals, size, angularity, and uniformity)

angularity

help show how far a sediment has moved

examples:

1. rounded clasts means it has undergone a lot of weathering which means it could have come from a peak-mountain stream

2. rock with sharp edges means it hasnt gone through as much weathering and would have come from a lower part of the stream

shales (clastic)

type of sedimentary rock; most ABUNDANT clastic rock; the form from the finest clay particles; BEST SORTING; form on floodplains; lake beds; and ocean beds; can form in both continental and marine sedimentary environments steep or shallow; shales can vary in color depending on composition (black shales are rich in organics and form where there was once abundant vegetation; GREEN shales include clays in their composition; RED shales contain hematite)

PA geology

in PA, clast size of sedimentary rock decreases from the southeast to the northwest;

conglomerates are found in the southeast

sandstones are found in central PA and the mountains

shales are found in western, northwestern, and central PA and in the mountains;

Happy Valley sits on a limestone bed while Mt Nittany is capped by sandstone

can be concluded that state college used to lay under a shallow sea 450 million years ago

state college must have also been near equator around 450 Ma

chemical sedimentary rocks

form when minerals precipitate out of solution, leading to crystallization; typically occurs when a solution becomes supersaturated by evaporation, or when biological processes pump mineral compositions into water to form shells (creating limestone)

limestones

composed of fine-grained calcite, and can include fossilized shells; generally formed in marine and tropical environments

loess

unstratified sediment deposited by wind; can transport very fine particles long distances

cross-bedding

wind and water currents can cause this; it is horizontal layers that internally consist of angled layers

water vs. wind

both forces generate stacked layers and can form cross-bedding

-cross-beds formed by water are generally much thinner than cross-beds formed by wind

sedimentary structures

often preserve information about ancient environments; increasing pressure and temperature, along with chemical cementation, are crucial to lithification (sediment to rock) process

uniformitarianism

states that forces that sculpt the Earth today are the same forces that acted on the Earth eons ago

-exhibited in mud cracks and ripple marks in sand today that are similar to rock textures formed millions of years ago

-these processes include volcanic eruptions, climate change, and any other fairly common process that occur regularly over time

-sand dunes forming today are similar to sandstone mounds formed millions of year ago

-----change in the wind direction creates cross-beds in ancient dunes, so the cross beds can tell us the direction of the wind

catatrophism

focuses more on sudden and non-frequent events that change the Earth's surface, such as a meteorite impact; OPPOSITE OF UNIFORMITARIANISM

geological time scale

relates rock layers to time;

time is split into eras

eras are split into periods

periods are split into epochs

-Precambrian era to present day

stratigraphy

different rock layers indicate different conditions in an area at the times each layer was formed

law of original horizontality

sediment layers are initially deposited horizontally, forming horizontal rock layers/strata

law of superposition

oldest rock layers were deposited first, with younger rock forming on top

correlation of strata

correlating layers in different areas can be used to understand the geologic history of areas that share similar layers (i.e same rock = roughly same formation/deposition time)

uncomformity

interface between rock beds caused by erosion that indicates sediment deposition was not continuous; indicate that part of the rock record in an area is missing; caused by erosion or a period of non-deposition, that indicates sediment deposition was not continuous

nonconformity

formed with a layer of igneous rock on the bottom as the erosional surface and a sedimentary later formed above; often sign of some sort of igneous intrusion

disconformity

formed when part of a layer of sedimentary rock is missing and a new layer of sedimentary forms over top; formation of rock layers on a shore as sea level changes over time; usually difficult to identify

angular uncomformity

displayed when the angle of rock layers is much different from the angle of the rock layers above them; this is formed when original layers are uplifted and folded, later eroded, and finally new layers form over the erosion surface (changing sea level if vital in this unconformity as well)

fossils

fossil formation is helpful in stratigraphy correlation

more on fossils

correlation of rock layers in different areas focuses on the rocks that formed at the same time in each area

principle of fossil succession

states that fossilized organisms appear and disappear in the rock record in an orderly fashion

criteria of fossil formation

for a fossil to form, an organism should follow one or some of the following:

-die by freezing (frozen mammoths)

-die in a low-oxygen environment (tar pits, amber, ocean bottom)

-rapid burial (hard body parts perserved

-lack transformation of material after burial (trace fossils)

do fossils often correlate with different areas?

yes

trace fossils

have no hard parts; but indicate the presence of organisms; dino footprints

index fossils

have known times of formation that are used to correlate rock layers; the shorter the span of formation time of a fossil, the more accurately rocks can be correlated

when did life start in terms of period?

cambrian period

what period are we currently living in?

holocene epoch

atomic #

number of protons

atomic weight

average mass of an atom of a given element

isotopes

atoms of the same element that have differing numbers of protons

mass number

number of protons plus number of neutrons

radioactive isotopes

transform spontaneously into an atom of another element in a process known as radioactive decay

radioactive decay

The breakdown of a radioactive element, releasing particles and energy

alpha decay

unstable parent atom emits a helium atom, resulting in a loss of 2 protons and 2 neutrons from the parent (decrease in atomic number and mass)

beta decay

changing a neutron into a proton, loss of an electron, resulting in an increase in atomic number, but no change in mass number

electron capture

parent captures an electron which transforms a proton to a neutron, results in a decrease in atomic number but NO CHANGE IN MASS #

half-life

amount of time it takes for half the parents material in a sample to decay into daughter material is known as this

losing daughter material

or adding parent material will give a measured age that is younger than a rocks actual age

adding daughter material

or losing parent material will give a measured age that is oder than a rocks actual age

sedimentary rocks and dating

sedimentary rocks must be dated by finding the ages of igneous rocks in an area and determining an age range for its deformation

older rocks

older the rock is, the large the error in measured age will be

eons

phanerozoic --> precambrian[proterozoic, archean, hadean]

era

cenozoic, mesozoic, paleozoic

period

quarternary, teritary, cretaceous, jurassic, triassic, permian, Pennsylvanian, Mississippian, devonian, silurian, ordovician, cambiran

(youngest to oldest)

important year boundaries

tertiary (66Ma) cretaceous, triassic (240 Ma) Archean, Archean (3800 Ma) Hadean

How are batholiths different from flood basalts?

batholiths are typically coarser-grained and more silicic than flood basalts

Which of the following rock types will weather the most quickly?

Basalt - a lot of iron - weather quickly (50% silica) - finer grain = weather quickly

what do we call an intrusive igneous rock that is chemically identical to a basalt

Gabbro

Does cutting down rain-forests will lead to a world-wide increase in the weathering of marble statues?

YES - because the forest acts as a carbon dioxide sink - a tree takes carbon dioxide out of the atmosphere (photosynthesis)

what factors control the character of a soil?

parent material, time, climate, slope, plants and animals

slopes and character of soil

steep slopes often have poorly developed soils; optimum is a flat upland surface; steep slopes and young exposures - POOR soil development; gentle slopes and old exposures - GOOD soil development

which crop and cultivation technique will minimize soil erosion

apples - land between the rows of trees is planted in grass and not cultivated

soil profile

soil forming processes operate from the surface downward; soils are separated into horizons; zones/layers of soil = HORIZONS

Horizons in temperate regions

O - organic matter

A - organic and mineral matter

E - zone of leaching

B - zone of accumulation

C - partially altered parent

*** O and A together called TOPSOIL

Water saturated sediment

water fills in the pore space between grains

liquefaction

water completely surrounds all grains and eliminates all grain to grain contact; sediment flows like a fluid

landslide triggers

water; steep slopes; earthquakes; sparse vegetation

styles of mass wasting

fall - mass travels through air

slide - mass is dry and slides along ground

flow - mass is west and flows along groudn

creep - mass moves very gradually

slump - mass moves along arcuate surface

varieties of mass - earth, mud, rock, debris