Intro to physical geography final

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Earth' internal structure

crust, mantle, outer core, inner core

Earth's core

1/3 of Earth's mass, enormous pressure, iron and nickel,

Inner core


Outer core

molten magma

earth's mantle

Largest of interior zones, solid rocky material, less dense than core, plastic solid, outermost layer: behaves like an elastic solid (rigid) lithosphere: (upper most mantle and crust)


upper most mantle and crust


upper mantle, tectonic forces come from movement of asthenosphere,
moho discontinuity

earth's crust

1% of earth's mass, exterior of lithosphere, density: oceanic crust (basaltic) more dense than continental crust (granitic)

earth's crust

is less dense than the mantle or core and is quite thin in comparison

the average thickness of the crust is?

20-25 miles
oceans: 1.9-3 miles thick
continental mountain systems are as thick as 43 miles

basaltic rocks

dark colored, fine grained and iron rich

granitic rocks

high in silica content and are lighter in color

igneous rocks

molten rock material cools and solidifies
magma: below surface
lava: at surface
2 major categories of igneous: extrusive, intrusive

sedimentary rocks

accumulated sediment
unconsolidated minerals that have been eroded transported and deposited

organic sedimentary

coal, clastic limestone, chalk

chemical sedimentary rocks

dolomite, solutional limestone

metamorphic rocks

changed form due to enormous heat and pressure, harder, foliation

two major types of metamorphic rocks:

foliated (presence of platy or wavy surfaces)
nonfoliated(absence of platy or wavy surfaces)

continental drift

the idea that continents and other landmasses have shifted their positions during earth's history (close fit of continents and fossil records)

Who proposed the theory of continental drift?

Alfred Wegener in 1915

supercontinent pangea

all earth, all continents fit together, fragmentation and drift to current positions (pangea was not and will not be only supercontinent)

in the 1960s

scientist propose sea floor spreading along mid-oceanic ridges for plate motion

theory of plate tectonics

refers to the process of plate formation, movement, and destruction
helps answer why earthquakes and volcanoes occur where they do

lithosphere plates

float on top of denser asthenosphere in which convection occurs
comprised of lighter, less dense, granitic continental crust; and heavier, denser, basaltic oceanic crust

plates movement

driven by thermal convection-cell plumes in the mantle

3 forms of plate boundaries

divergent spreading centers, convergent subduction zones, and transform (strike-slip fault) boundaries

some examples of spreading centers

mid-ocean ridges-seen best in iceland
african rift zone- rift zone where a spreading center extends under a continent

plate divergence (pulling apart)

seafloor spreading
shallow earthquakes
creates new ridges
most occur near oceanic ridges (iceland)

plate convergence (pushing together)

denser plate forced under lighter plate
known as subduction
examples: nazca plate subducts beneath south america, Japan

3 types of converging subduction zones

continent-continent zone- indian/ eurasian plate boundary
ocean-ocean island arcs: aleutian islands, japan, Phillipines, Indonesia
ocean-continent zones, producing a volcanic arc, often with folded mountains further inland- Andes, South America; Cascades, North America


neither converging or diverging, but instead plates slide alongside each other as they move in opposite directions

San Andreas Fault

Pacific plate is moving northwest in relation to N.A. Plate at a rate of 3 inches a year
In 100 million years, Los Angeles will move alongside San Francico

topographic expression

intensely folded and heavily locally faulted mountains, such as the transverse Ranges NW of Los Angeles


evidence of present-day tectonic activity
ground motions of earth caused when accumulating tectonic stress is suddenly relieved
seismic waves

measuring earthquake intensity

earthquake intensity-richter scale
modified mercalli scale

earthquake hazards

2004 Sumatra-Andaman Earthquake in quake and ensuing tsunami
killed 300,000
9.1 magnitude
Pakistan (7.6)
Kobe, Japan (7.2)
Mojave Desert (7.5)
Loma Prieta (San Francisco Bay) in 1989
Northridge earthquake (1994 6.7 magnitude)
Mexico City (1985 8.1 magnitude)

3 Principal Tectonic Forces

Compressional, Tensional, Shearing


upward-folded structure


downward-folded structure


simple one-step flexure
example: san rafael swell in Southeastern Utah

Types of Faults

Normal Fault, Reverse Fault, Thrust Fault, Overthrust, Strike-slip fault

Upthrown block

portion of faulted land moved locally upward relative to adjacent land

downthrown block

portion of faulted land moved locally downward relative to adjacent land


uplifted blocks


downdropped blocks

death valley

an enormous graben

grand tetons

fault scarp modified by both glacial and stream incision

tectonic fault scarp

stream erosion cuts deep v-shaped canyons, leaving flatirons or triangular facets between the canyons

Landforms resulting from igneous processes are related to

volcanism (extrusive)
plutonism (below Earth's surface)

plutonism and intrusions

igneous intrusions (plutons)
classified by size shape and relationships to surrounding rocks

types of igneous intrusions

sill, dike, laccolith, stock, batholith, others, volcanic neck

discordant intrusions

cut across pre-existing layers/units

concordant intrusions

parallel that rock


massive cuts across
very large bodies of plutonic rock at least 100km in map view


massive parallel
basically an inflated sill a situation in which magma is injected between two layers with enough pressure to force the overlying rock to dome upward producing mushroom shaped intrusions that create domal uplift overhead
best examples: La Sal, Henry, and Abajo Mountains of South East Utah


tabular parallel
a concordant tabular intrusion is a small intrusion in which magma was injected between two pre existing rock layers
sills (like dikes) are comprised of very hard, resistant rock that may form near vertical cliffs such as at the Garden Wall in Glacier National Park


tabular cuts across
definition: a small discordant, tabular intrusion in which magma was injected into a crack, resulting in a sheet of igneous rock that cross-cuts adjacent layers, frequently occur as swarms near volcanoes, or near near-surface intrusions such as laccoliths, volcanic necks, or stocks


magma bodies that solidify beneath earth

Some of the best dikes in the world occur where?

At the Spanish Peaks in southern Colorado the peaks are believed to be adjacent stocks


a medium sized intrusion less than 100 km but still generally mappable

batholiths of the western united states

baja california batholith, sierra nevada batholith, idaho batholith, coastal range batholith

the rock of batholiths

cools deep underground producing rock with large interlocking crystals that provide stability and resistance to erosion

volcanic neck

a cylindrical shaped landform standing above the surface created by magma solidifying in the vent of a volcano erosion of the sides of the volcano exposes the neck

fissure eruptions

eruption occurs along fissures/fractures/rifts, pouring out great volumes of lava spreading out in sheets over great surface areas

central vent eruptions

eruption occurs from a central conduit leading downward. These produce what we refer to as Volcanoes

what causes volcanoes

plate tectonics: certain colliding plates: continental vs oceanic and oceanic vs oceanic
diverging plates(spreading centers e.g. Iceland)
hot spots: areas not associated with plate boundaries

Hot spots: Mantle Plumes

Magma rises through plate
50+ hot spots in world
stay stationary while plates move over them
create linear set of volcanoes (Hawaii)


building but still 1000m below surface
will eventually replace the Big Island
1/2 million to 1 million years until it reaches surface

nature of volcanic eruption dependent on:

mineral composition, heat, pressure, pyroclastic materials (ash and tephra)

composition of the magma

basaltic magma has less silica is therefore more fluid, less sticky. Ryholitic (extrusive form of granite) Magma high in Silica content is more viscous; viscous lava temporarily plugs outlets, builds up pressure, causes more explosive eruptions

temperature of the magma

Hot lavas, typically found at Spreading Centers and Volcanic "Hot Spots", are more fluid than cooler lavas. Basaltic lava melts at ca. 2000°F, Rhyolitic lava at only 1200°F, thus basaltic eruptions are more fluid and tend to be less violent than rhyolitic eruptions.

gas content

More gas content, more explosiveness. Cooler lavas have more gas separated out in them, and thus have greater potential for explosiveness.


Includes 2 types of materials:
Pre-existing rocks torn from the sides of the current eruption vent or fissure
Liquid magma that cools and solidifies in the air.
Both types collectively called "Pyroclastics", from Pyros (fire) and Clastos (broken fragments)
Pyroclastics come in a range of sizes, from fine-grained ash to cinder-sized chunks to large bombs.

liquid magma

upon reaching surface either through a vent or fissure is called lava


includes steam as well as more noxious and sometimes deadly gases including carbon dioxide

volcanic landforms

depends primarily on explosiveness

6 major kinds (least explosive to most explosive)

Lava flows
Shield Volcanoes
Cinder Cones
Composite Cones
Plug Domes

lava flows

Basalt is the most common
Small potential for explosive eruption
Joints and columnar-jointed basalt flows (areas of slower cooling).
Pahoehoe - "ropy", fluid-flowing lava, recent pahoehoe flow on flank of Kilauea volcano, island of Hawaii
flood basalts
basalt plateaus: columbia plateau, deccan plateau in India

shield volcanoes

typically built by eruptions of fluid, basaltic lava, they take on the appearance of a shield with the convex side facing upward, Numerous basaltic lava flows piling up
Gently sloping, shield-shaped cone
Hawaii, Iceland
Not very explosive, but still damaging

composite cones

Effusive or explosive
Composite of lava and pyroclastic
Aka Stratovolcanoes
Pyroclastic flows
Concave slopes that are gentle near the base and steep near the top
Fujiyama, Vesuvius, Rainer, St Helens
built by alternating eruptions of lava and pyroclastic material, form tall conical mountains

plug domes

Viscous rhyolitic lavas ooze out on ground surface like thick toothpaste and do not flow far from central vent, Tend to have very irregular summit surfaces rather than a distinct crater typical of most other volcanic cones

cinder cones

Smallest type of true volcano
Rhyolite composition
Steep, straight sides and a large crater in the center
Craters of the Moon, ID
Sunset Crater, AZ
Capulin Volcano, NM
are constructed from the deposition of cinders and other pyroclastic material

spatter cones

Develop around small vents where molten lava is tossed into the air by the force of gases in the magma. Blobs of lava fall around the vent, where they weld themselves together and accumulate, building up a small "bloop-bloop" looking cone.


unusually large central depressions of volcanoes measured in kilometers to tens of kilometers
Caused by:
Explosion of summit area.
Collapse of interior of the cone, following ejection of immense volumes of pyroclastics.
Subsidence due to draining of a magma chamber by flank eruptions
example: crater lake, oregon

lava tubes and caves

Molten interior of a lava flow continues to flow when sides and overlying surface have solidified; this evacuates lava, leaving behind long linear tubes that may be exposed by erosion as a lava "cave".

squeeze ups

mounds formed by molten lava pushing up through earlier formed crust


The disintegration and decomposition of rocks and minerals at the earth's surface as a result of physical and chemical action
Prepares the way for erosion by weakening rock and making it more susceptible to mass movements and removal by other agents of erosion

Controls of Rate and character of weathering

parent material, climate vegetation, topography, time

parent material

physical and chemical properties of bedrock have profound influence on both rates and type of weathering

Time as weathering control

All other factors being equal, the longer a rock or surface has been exposed, the more it will be weathered.
Pleistocene glaciation "reset the clock" for many high latitude and high altitude landscapes, producing environments with very little weathering. Even less weathering on landscapes glaciated during the Little Ice Age, from about 1500-1850 AD.

Physical(Mechanical) Weathering

Refers to disintegration or breaking up of rock by physical processes without changes in chemical or mineral composition.Brought about both by:
Stresses originating within rocks (internal stress)
External stresses
Thermal Expansion and Contraction
Freezing and Thawing
Growth of Crystals
Wetting and Drying (Hydration)
Organic Activity


the release of pressure by removal of overburden, when rock is uplifted or exposed at the surface by erosion high confining pressures are reduced and rock expansion may occur sufficiently rapidly to produce fracturingUnloading is most common in massive granites and thick sandstones.

sheeting joints (exfoliation fractures)

best developed near the surface, becoming more widely spaced at depths
exfoliation domes: form by concentric exfoliation of granite
exfoliation along vertical walls in massive sandstone or granite may produce broad arches

granular disintegration

Differential thermal expansion and contraction of individual mineral grains in coarse crystalline rocks

freeze-thaw weathering

Also called frost weathering (ice wedging)
Water freezes it expands 9%
Pipes bursting
Angular blocks
Effective in the upper-middle and lower-high latitudes

optimum conditions for the wedging effect of freeze-thaw

a supply of water
many alterations of freezing and thawing
yet also needs sustained freezing well below 32°F/ 0°C so that masses of ice will grow; most spectacular at higher latitudes and high altitudes above treeline

growth of crystals

Results from evaporation of water, inducing crystallization of minerals. Salt crystal growth perhaps the most common form of disintegration of rock by crystals.
Crystal growth induces pressures similar to those associated with frost shattering.
Particularly effective in permeable sedimentary rocks such as sandstone.

salt weathering

Responsible for the development of alcoves and closely spaced holes.
Holes are known as tafoni (from Corsica), and their close grouping is known as "stone lace", "stone lattice", "alveolar weathering", or "honeycomb"


a disintegration process rock can crack apart into tiny chips and spalls


clayey siltstone and sandstone especially susceptible to this process

pedestal rocks

often originate by slaking, where an overlying resistant caprock becomes undermined and isolated by erosion until it resembles the head of a mushroom.

organic activity

Plant roots grow and extend into bedding planes and joints, prying rocks apart. Large roots can wedge boulder-size rocks apart.

Physical weathering by animals

is largely a matter of mixing unconsolidated materials - worms, ants, rodents. Burrowing brings unweathered fragments into contact with chemical weathering agents, air and water.

chemical weathering

The decomposition of rocks by surface processes that change the chemical composition of the original material. Involves chemical reactions between the elements in the minerals of a rock and the atmosphere and/or groundwater.

Forms of chemical weathering

oxidation-reduction, carbonation


Oxidation occurs when a mineral, typically iron, combines with an oxygen ion in the presence of water. Changes ferrous iron (Fe++) into ferric iron (Fe+++), which is insoluble and precipitates out as a solid compound - typically a reddish brown crust, i.e., rust.


Minerals that contain calcium, sodium, potassium, or magnesium are changed to carbonates by carbonic acid.
Limestone, one of the most common rocks, is calcium carbonate, CaCO3 Carbonic acid forms from the combination of water and carbon dioxide, H2O + CO2


"an approach to geomorphology which explicitly considers the role of organisms". Encompasses both plants and animals


the study of the geomorphic effects of animals

Animals impact landscape via

overgrazing, trampling, wallowing, geophagy, digging for food/catching food, burrowing/denning/mound building, dam construction
All but dam construction can have substantial effects on valley hillslopes, dams affect stream courses and valley bottoms.

Trampling leading to erosion

Directly such as when trampling along the edge of a stream, pond, etc. causes hoof or paw chiseling, and bank sloughing and erosion.
Indirectly because it "prepares" soil for erosion via removal of vegetative cover, causes accelerated water runoff as soil bulk density is increased and permeability reduced.

bison trampling

Given that there were ca. 30-60 million bison roaming the North American prairie, effects surprisingly unquantified.
Areas around rivers, and at bison wallows noted in pioneer writings as being "trampled" and "heavy with trails".
Wallows described as "several meters in diameter".
Bulk density of soil in wallows, as a result of rolling and trampling, is significantly greater than the adjacent landscape.
Wallowing induced a bulk density increase of 17% relative to adjacent tallgrass prairie.
Compaction reduces infiltration, so that wallows serve as local ponds that can retain water for several days following.

calculating amount of material excavated from a typical wallow

circularity was assumed
area was calculated using the formula π r2.
For a range in radii of 1-5 m, area of wallows are calculated as 3.14 m2 - 78.5 m2.
Assuming an average depth of 10-30 cm, a 1-m radius wallow accounts for ca. 0.3 m3-0.9 m3 of sediment displaced.
For a wallow with a 5-m radius and an average depth of 10-30 cm, 7.8 m3-23.5 m3 of sediment is removed, although compaction via wallowing accounts for some of the apparent below-surface loss.

bird geophagy

Scarlet Macaws, as well as the other members of the Parrots and Macaws family, often visit clay licks to eat clay, a habit known as

soil ingestion by birds

Sandpipers probe & peck for invertebrates in shallow water and mud, consume sediment at a rate of 7-30% of their diets.
Canada geese, 8%.
Wild turkey, 9%.
"Thousands" of parrots visit clay licks at one time, no measures of the amount ingested.

African Waterholes

Created by synergistic activities of trampling, drinking, and geophagy of salt-rich soils.
Animals congregate, trample, expand margins of waterholes
Wallowing erodes sediment also - one elephant carried up to 1 cubic meter of sediment away after wallowing
Waterholes thus created may be up to half a square kilometer in size, although ca. 200 m across is more typical.

digging for food

A variety of methods for digging for food by animals, including:
pawing at the surface (ungulate herbivores)
digging/tunneling underground for food sources beneath the surface
excavating burrows for tasty bits within
scraping/raking the surface with claws
rooting with one's snout

hog rooting

In Spain, wild boars root for voles at alpine treeline.
In Australia, wild (feral) pigs have undermined earthen dams, fences, and dirt roads. A light aircraft landing strip in Queensland was "entirely rooted up by pigs and rendered completely unserviceable for aircraft".
A property owner of 200 square miles in Queensland reported that 10% (20 sq mi) of his land was rooted by pigs.
In Luxembourg, rooting by wild pigs displaced "upwards of a ton of earth" in a few days, leaving behind pit-and-mound microtopography 40-70 cm deep.

burrowing and denning

"Fossorial" - adapted to burrowing
Fossorial animals found on all continents
Burrows range in degree of construction along a continuum from a simple hole to elaborate underground complexes

gopher rates and amounts

In the Wasatch Mountains of Utah, gophers covered the surface with 11-14 tons of sediment per hectare per year.
In the Colorado Rockies along Trail Ridge Road in RMNP, gophers displace 4-6 tons of sediment per hectare per year.

prairie dog burrowing and towns

Prairie dogs ranged over 600,000 square miles of North America in the early 1800s.
As late as 1919, they covered more than 20% of the potential area of North American mid- and short-grass prairies.
The big prairie dog town in Texas near the Prairie Dog Fork of the Red River at the beginning of the 20th Century contained an estimated 400 million prairie dogs and covered an area 160 km wide by 400 km long.

prairie dog burrowing continued

A typical prairie-dog burrow system has two entrances, is ca. 1-3 m deep, ca. 15 m long, and has a diameter of 10-13 cm. Each burrow system mixes ca. 200-225 kg of soil, much of it deposited as mounds around the entrances, with 50-300 burrow entrances per hectare (Whicker and Detling, 1988).300 systems occurred per hectare, with 200-225 kg of soil mixed per each system, then each hectare occupied undergoes 60,000-67,500 kg of soil mixing by prairie dogs.
Considering that prairie dogs currently occupy only about 1.5% of the pre-Contact range, it seems safe to say that an enormous zoogeomorphic influence on the hydrology of the Great Plains region was removed by efforts to eradicate prairie dogs.

grizzly bear den

An individual grizzly bear digs a new den each winter, moving 4.3m3 of excavated material downslope. They also move large quantities of sediment in search of plant and animal food sources.

puffin burrows destroy island

1890 there were over half a million puffins on Grassholm, an 8.9 hectare island. Densities of breeding puffins were 2-3 pairs per square meter. Vegetation was nearly totally destroyed, and the soil was so severely tunneled by puffin burrows that it collapsed and was extensively eroded. By 1928, all that was left of the island were isolated pillars and tussocks of turf, and about 200 puffins.

colonial seabird burrowing

burrow lengths average 1m, can be over 2m long


teeth grow continuously throughout lifetime, webbed feet

effects of beaver dam construction

Elevate water table, increase riparian and pond habitats
Reduce stream velocity, inducing sedimentation in ponds and reduced erosion downstream
beaver ponds dominate the landscape in the headwaters of Red Eagle Creek, Glacier National Park

calculating sediment volume and rates in beaver ponds

Ponds of known age needed
Pond area measured
Sediment thickness sampled across floor of pond and averaged
Average thickness x pond
area = volume of sediment per pond

Thickness ÷ age of pond
life in years
= rate of accumulation per year

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