Geology Exam 2

principle of uniformitariansim

"the present is the key to the past"

principle of superposition

(old on bottom, new on top) -each layer of rock is younger than the layer below & older than the layer above

Formation of Aeolian Crossbeds and Frosted Sand

*wind a) salting and rolling grains land on slip face b) unstable accumulation builds up c) accumulation cascades down to base, advancing the dune *frosted sand, lack of fossil evidence and cross-beds---> desert

Crater Lake

- North America's Deepest Lake -4.6 trillion gallons of water form rainfall & snow melt in 250 years -1,932 feet deep - >500 inches of snow/year -ashfall deposits near Crater Lake are up to 60 ft thick and contain artifacts of the Klamath Native Americans

Nez Perce Trail

-1877, the US army pursued approximately 800 Nez Perce across the pacific NW -they surrendered 40 miles from the Canadian border on October 5th

Navajo Sandstone

-20-30 ft. thick, well defined cross-beds -sand is well sorted, frosted, & almost entirely quartz

Mt. Rainier Attributes

-4393 meters (14,410 ft) -highest peak in the cascades range! -Active -largest single-peak glacier system in the contiguous states -Most likely the most DANGEROUS volcano in the cascades -Lahar danger is HIGH around Mt. Rainier -close to population centers -capped by snow and ice (glaciers)

limitations in radiometric methods of dating rocks

-CANT be used on sedimentary rocks

Cryptogamic Soil

-Cyanobacteria, lichen, mosses, algae, and microfungi capable of holding 40 times its volume in water- very fragile -seismic exploration of the colorado plateau

first person credited with understanding the geological significance of the Grand Canyon

-Major John Wesley Powell.... wait maybe Jules Marcou?

cultural history of Crater Lake

-Makalaks (pre Klamath) believed that Crater Lake was so holy that looking at it could cause death

Zion National Park

-Zion canyon is cut into the Jurassic (144-208ma) -from April-October, Zion Canyon is accessible only by mass transit -Virgin River in Zion National Park is only major river in the western US that isn't dammed -Narrow & deep slot canyons are a popular tourist destination

ash columns & ash fall (Tephra)

-a mixture of gas and rock fragments that erupts into the air from a volcano -volcanic ash clogs combustion, burry homes -good for soil and plants -may reach altitude of 25 miles or more

lava domes

-a relatively small volcano in diameter formed by the eruption of sticky, silica rich lava around a central vent -may form prior to or after eruption -their collapse often triggers pyroclastic flows -very cool, viscis (thick), squeeze out & plug like wine -many volcanoes are triggered by lava domes

unconformity

-a surface between two rock units of different ages and represents a period of erosion -unconformities are classified and recognized based upon the rock type and relationship of the geologic units -types: nonconformity, angular conformity, disconformity

Cascade Mountains

-a volcanic arc is a chain of steep, composite (stratovolcanoes) volcanoes that form above a subduction zone, formed on the edge of a continent -composite or stratovolcanoes are composed of lava flows and pyroclastic material and have relatively steep slopes -contain explosive volcanoes formed as fluids rise from the top of the subducting plate and generate magma as they melt their way to the surface, region awaits sudden release of energy locked between the converging plates as a devastating earthquake *most active is actually where the pacific plate subducts beneath the Alaska peninsula and aleutian islands

mountains and uranium

-also in the Tertiary, laccoliths (igneous rocks) were intruded into the sedimentary rocks on the colorado plateau. -these intrusions warped the overlying sedimentary rocks and, after erosion, form the small, isolated mountain ranges on the Colorado Plateau

Humans on the Colorado Plateau

-artifacts of nomadic cultures -10,000 BCE -Anasazi Civilations- 1-1300 CE -"The Basket Maker Period" -corn and squash cultivation, permanent settlements -"The Pueblo Period" - active water control projects, high quality pottery, leisure culture -small bands of nomadic hunters and gatherers originally from western Canada (adopted farming, domestic animals and pottery making) -resource exploration (copper and gold mining, intensive logging and grazing, uranium exploration (peak) world's largest coal mine opens, water control systems)

Bryce Canyon National Park

-bryce canyon is a series of basins (amphitheaters) eroded into the side of a cliff -pink cliffs of the eocene claron fm -during the eocene, large lakes covered much of the colorado plateau -Known for its spires or HOODOS -Hoodos formed from differential erosion along joints-more resistant rock protects the underlying less resistant rock from erosion -hoodos are formed primarily by water erosion

continental hotspots

-complex and produce biomodal volcanism (both Mafic and Felsic volcanism NOT intermediate) -heat transfer melting -when you melt continental crust, you get felsic (very explosive)

Arches National Park

-contains the largest concentration of these features anywhere in the world- over 300 -landscape arch: 300 feet across: is the longest in Arches National Park

assumptions made when utilizing the method of radiometric dating*

-decay rate is constant -it is a closed system (no material lost or gained) -all daughter product is a result of radio active decay of parent materials -our analytical methods are accurate *most accurately used on igneous rocks

Colorado Plateau

-deeply incised by rivers -exposes the most complete geologic history of North America -80% public lands (including Navajo & Hopi Reservations)

Desert Varnish

-deposits of iron oxide, manganese oxide and silica due to evaporation of water from the surface (called Desert Varnish) leave a dark coating on the rocks

differential weathering/erosion

-different rock units will weather and erode at different rates, causing a stair-step pattern

pyroclastic flows

-dome collapse & expanding gasses may generate pyroclastic flow

Yellow Stone National Park

-established March 1, 1872 -very FIRST national park -during the past 10 years, yellowstone averages 3 million visitors per year

Mt. Rainier National Park

-established March 2, 1899 -2 million visitors annually

velocity of rivers

-fluvial environments (erosive capability of streams ability to transport sediment, is directly related to the velocity, which is primarily dependent upon the gradient and discharge -water transport leads to mature, rounding, sorting, and concentration of minerals *steep slope= greater velocity (speed)

Sea Level Changes

-formation of Pangaea at the end of the paleozoic caused a global fall of sea level -by the jurassic, most of the US was exposed above sea level and the Atlantic Ocean was opening

geothermal features

-geysers, hot springs and mud pots are formed when water is superheated by the magma chamber at depth- data indicate magma <4km below the surface

inclusions

-if a piece of rock is completely enclosed by a different rock, the piece (inclusion) is older

mountain ranges on the colorado plateau are composed of which types of rocks?

-igneous

cross cutting relationships

-igneous intrusions and faults are younger than the rocks that they intrude or break

Yellowstone calderas & resurgent domes

-inflate and deflate--> movement of magma & gasses

Jurassic on the Colorado Plateau

-large amounts of sand was exposed and moved around by wind currents in large Erg Complexes "sand seas"

how do geysers work?

-require a restricted conduit (a channel for conveying water or other fluid) and storage chambers -often have a cone around the opening made of silica sinter or "geyserite" (this is sio2 that is dissolved at depth and re precipitated when the water cools at the surface)

Caldera Formation

-rising magma bulges the surface -cracks form and propagate down, intersecting the magma chamber and causing eruption -overlying rock collapses, forming the Caldera -at Yellowstone, the caldera is largely filled in with younger lava flows -after formation of caldera you get small volumes of mafic magma, there for they produce biomodal lava *felsic--> pyroclastic debree-->hole = caldera Crater= collapse Caldera= materials erupt

dams and the grand canyon

-river discharge is consistent and less than natural conditions -downcutting of the canyon slowed -rocks are not cleared from the channel creating more rapids

disconformity

-rocks above and below the unconformity are horizontal and undeformed -usually recognizing a disconformity requires fossil evidence

angular unconformity

-rocks below the unconformity are folded or faulted (deformed) while the ones above are not

nonconformity

-rocks below the unconformity are metamorphic or igneous intrusive (formed inside the earth) while the ones above are sedimentary or igneous extrusive (formed on surface) -represents a profound amount of uplift and erosion

pyroclastic rocks

-rocks formed during explosive eruption examples: -pumice: frothed glass -tuff: volcanic fragments commonly welded together (if flow is hot and the tephra (pieces of ash, crystals and rock) stick together, creates tuff)

Rocks at Bryce Canyon

-rocks were deposited in a large freshwater lake called Lake Flagstaff -contain fish fossils from the Eocene green river formation -sediment--> fish fossils found in SHALE (clay) rocks (fine grain, fine sediments)

principle of original horizontality

-sedimentary rocks are deposited as horizontal layers -therefore, if sedimentary rocks are folded or faulted, the deformation occurred after deposition

Lahar are formed due to

-tephra mixing with meltwater

snake river

-the calderas are coered by younger baslat flows -composiion of the volcanic rocks @ yellowstone, biomodal (lots of felsic, little mafic)

dams and sediment transport

-the sediment is deposited behind the dams and fills up reservoirs -the canyon is sediment-deficient and beaches and sand bars in the canyon are eroded

The inner gorge

-the steep inner gorge is composed of igneous intrusive and metamorphic rocks -these rocks were formed from high temperature and pressure beneath a mountain range *why is it steeper than upper portion? -because rock is hard to erode (interlocking)

what was the intent of the experimental "flood" in the Grand Canyon in March and April 1996, November 2004, and March 2008?

-to evaluate whether artificial (that is, controlled) floods released from the dam could be used in conjunction with the sand supplied by downstream tributaries to rebuild and sustainably maintain eddy sandbars in the river in Grand Canyon National Park.

lahars

-volcanic ash mixed with water -can occur without warning long after an eruption -(mud flows)

Geologic Time Scale

-was developed in the 19th century using relative dating techniques -the numbers were not added until early in the 20th century using absolute dating techniques

Navajo Sandstone Story

-widespread sand dunes cover the Colorado Plateau -Pangaea Forms, causing the oceans to retreat from the continents

comparing the most recent eruptions of yellowstone NP to recent eruptions in the Cascades Volcanic Arc

-yellowstone eruptions are much larger in volume

Mt. St Helens

-youngest of the cascades -eruptions in 1980 and 2005

result of prolonged physical and chemical weathering

...

Eruption of Mt. St Helens 1980

1) As magma rose, the north flank (side) began to bulge outward 2) Earthquake beneath the mountain caused the bulge to fail as a giant landslide 3) Sudden release allowed gasses to expand outward causing a LATERAL BLAST 4) lava dome grew for 6 years inside the crater formed by lateral blast

Formation of Arches

1) The rocks are jointed -salt domes cause jointing in the overlying rocks 2) Differential Erosion occurs along the joints creating "fins" -wind + water = deepen joints into "fins" 3) Erosion along geologic contacts causes collapse of the overlying rocks Geologic contact: where rocks with different resistances to erosion meet (**** ARCHES ARE FORMED PRIMARILY BY WIND EROSION)

what factors control the type and rate of weathering?

1) climate: -temperature & rainfall *more rain= chemical weathering *little rain= physical weathering 2) parent material: -mineral solubility & rock structure -Differential weathering- masses of rock don't weather uniformly , one of the most important factors are the variations in the COMPOSITION of the rock -more resistant rock protrudes as rides or pinnacles or as steeper cliffs on an irregular hillside *Rock composition, climate, & pre-existing conditions control rates of wearthering.

two end member morphologies of rivers

1.) Meandering Streams: -forms where the river flows over easily eroded terrain and the topography is gentle 2.) Braided Streams: -forms where the river carries a high sediment load and there are large fluctuations in discharge

diagnostic characteristics of wind-blown sediment and resulting rocks

Abrasion: sandblasting causing etching, pitting, smoothing, and polishing of rock surfaces exposed to windblown sand

Issues in Yellowstone

Bison Issue -many bison carry brucellosis virus which causes domestic cattle to abort their calves *current policy: all bison who leave the park are killed Snowmobile Issue: -approximately 95% of yellowstone is affected by noise and/or air pollution from snowmobiles -Oct. 16, 2009: YNP revieses # of snowmobiles to 318 day and 78 coaches Wolf Issue: -overpopulation of elk has been a problem for many years -1995 wolves were reintroduced to YellowStone after a 60 year absence *they have done well & have been removed from the endangered species list as of May 4, 2009

Highest-Lowest Half Lives in Radiometric Systems

Rubidium-Strontium: 47 billion years Uranium-Lead: 4.5 billion years Potassium-Argon: 1.3 billion years Carbon-Nitrogen: 5730 years

THE PRODUCT OF WEATHERING

SOIL

Cascade volcanoes vs. Yellowstone

Cascade: stratovolcanoes that often produce pyroclastic flows and lahars Yellowstone: large calderas that produce bimodal volcanism (large felsic explosive events followed by mafic lava flows)

Understanding the scale

Cenozoic: Mammals (newest) (part of phanerozoic) Mesozoic: Dinosaurs (middle) (major mass extinctions on each border of mesozoic time periods) (part of phanerozoic) Paleozoic: Marine Invertebrates (oldest) (part of phanerozoic) Precambrian (before macroscopic life) -accounts for 84% of geologic time!!

metamorphic and intrusive rocks

Part 1: formation of crystalline basement -2.2 Ga, sedimentary rocks accumulated in a marine setting -these rocks were deeply buried, metamorphosed, intruded by granite and then uplifted and eroded to a near-flat surface Part 2: late precambrian sedimentation and mountain building -mafic volcanic rocks and sedimentary rocks were formed -these rocks were faulted and tilted and eroded as Australia rifted from North America

History of Yellow Stone

The Hayden Party: 1870 - no food, need to kill animals, shoot them if they leave The Mammoth Hotel: 1886 - 414 ft long, this hotel lost money and only existed for a few years First automobile enters Yellowstone: 1915

muav limestone

a chemical sedimentary rock with abundant marine fossils, some quite fragile

bright angel shale

a shale with abundant marine fossils- records a dramatic diversification of life

Mt St Helen's sediment dam

been constructed to contain the sediment in the post-eruption lahars

marine deposition

clastic sediments decrease in size with increasing water depth -chemical sediments form where clastic input is low

difference between conglomerate, sandstone and shale sedimentary rocks

conglomerate: when buried and cemented sandstone: made of sand-sized grains, mostly quartz, that were deposited in streambeds or on beaches (in lakes or deeper parts of the ocean, where water is quiter, finer particles of silt and mud accumulate) shale: burial, compaction, and cementation of rocks. Chemical sedimentary rocks: -limestone: in warm climates, shell fragments of marine organisms dissolve in seawater, precipitating out as calcium carbonate. This fine lime mud eventually turns into limestone -evaporite: a natural salt or mineral deposit left after the evaporation of a body of water.

desert pavement

distinctive surface caused by wind removing small particles of sediment and leaving larger pebbles behind

Paleozoic Rocks

flat-lying paleozoic sedimentary rocks form the upper, widest portion of the Grand Canyon- they record the surface conditions on the Colorado Plateau

control of the colorado river

government began a program to develop the Colorado River for: 1) flood control 2) irrigation 3) electricity generation benefits: hydroelectricity, irrigation, recreation consequences: arid climate, apportionment exceeds capacity so dams disrupt the geological processes and natural environment *colorado river has entrenched because the colorado plateau has experienced rapid uplift

how are geysers different than hot springs or mud pots?

hot springs: colors are due to microbes that live at different temperatures mud pots: form where the rock is altered to clay and water flow is low

breaking rocks into smaller pieces.....

increases the surface area to volume ratio

rounding

indicates how far the material was transported

sorting

indicates the mechanism of transport (water,wind,ice) *far down the river, rocks will be sorted well and fine grained

Triassic age sedimentary rocks in North America are commonly bright red in color. This is caused by

iron in the minerals oxidizing in contact with air

hot sports often occur at_____

locations within plates

the rocks found at craters of the moon NM are primarily

mafic

what is marine transgression & how would you recognize it in the rock record?

marine transgression: -occurs due to sea levels rising and we can recognize marine transgression through rock records because of the sediments sandstone, mudstone, and limestone common rock records relating to marine transgression are found through interpreting cross sections meaning: 1) first recognize the rocks, 2) second determine the order in which they are formed 3) lastly figure out a sequence of events that account for all the rocks you are observing

chemical weathering

minerals are changed into more stable components due to interaction with water rich in carbonic acid (water + carbon dioxide) Leaching: the removal of soluble components (this process changes the rock composition AND the water composition Dissolution: carbonate rocks & minerals are particularly prone to dissolution- caves & sinkholes are formed Oxidation: chemical combination of an element with oxygen -oxidation of iron in minerals gives rocks a reddish color

volcanic products of the yellowstone hotspot

more frequent high-low: -small hydrothermal explosives (least destructive) -strong earthquakes (semi destructive) -lava flows ( 100 per million yrs.. pretty destructive) -caldera forming eruptions (1 to 2 million years.. VERY destructive)

timeline of rock formation:

mountain building, metamorphism, intrusion, then erosion then rifting, sedimentation, deformation, then erosion then sea level rise, sedimentation

legend of mt. st helends

northwestern native americans called it Louwala clough--> smoking mountain

radiometric dating

parent material: original unstable isotope (carbon14) daughter product: secondary stable isotope (nitrogen14) half-life: amount of time it takes for 1/2 of the parent material to decay to the daughter product -radioactive decay proceeds at a known rate therefore scientists can measure how long it takes for 1/2 a group of isotopes to decay *14C dating is used only for organic substances

the grand canyon supergroup

precambrian sedimentary rocks recording an ancient rifting event -other half is found in Australia

weathering

process where rock is broken down at or near the Earth's surface to form sediment

relative age dating methods

relative: old on bottom, new on top (superposition) "this rock is older than that rock" absolute/numerical: this rock is 2 million years older than that rock

areas uplifted in calderas caused by magma gas movement are called:

resurgent domes

sedimentary structure

ripples: - dunes: -various types of depending on sand supply, wind speed and wind direction, amount of vegetation, and topography -Wind erodes material on the back side of the dune and deposits it on the front side of the dune. cross beds: -Inclined layers in sediment or sedimentary rocks that reveal the direction of wave or wind transport

physical/mechanical weathering

rock is physically broken into smaller pieces -examples: frost wedging: ice expands and forces the rock apart organic activity: roots may enlarge cracks in the rocks

hydrothermal alteration

rocks are chemically changed and often weakened through interaction with hot water

erosion

the incorporation and transportation of material (sediment) by a mobile agent *ice & wind -the size of sediment is the primary criterion fro naming clastic sedimentary rocks, while chemical sedimentary rocks are named based on the mineral precipitated -the size of the material deposited indicates the energy of the depositional environment *example: high energy is fast, and coarse; low energy is slow and fine-grained

Tonto Platform

the level, wide tonto platform marks the boundary between the Precambrian and the Cambrian rocks

obsidian

volcanic glass--> highest is2, felsic

Tapeats Sandstone

well-roundd and well-sorted quartz sandstone and conglomerate with abundant trilobite fossils