128 terms

Intro to physical geography final

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