Physical Geography

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lithosphere

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the solid portion of the earth

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geomorphology

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the study of
-land forms
-their origin
-characteristics
-distribution

(processes which shape the earth)

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topography

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surface features of a particular place or region

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uniformitarianism

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physical processes active in the environment today have been operating at the same pace and intensity throughout geologic history

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rapid changing geologic features

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-volcanic explosions
-floods
-beach erosions

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slower changing geologic features

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grand canyon

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geologic time

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earth: 4.6 billion years old

(judged by the decay of radioactive rocks)

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when did dinosaurs become extinct

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66 million years ago

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when (aprox.) did human beings appear on the earth

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2-3 million years ago

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geologists divided the earth into...

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eras/periods/epics

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holocene

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the past 10,000 years since the end of the last ice age

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pleistocene

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covers 1.65 million years prior to the last ice age

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the earth appears to be a sphere comprised of...

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several different layers

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the inner core

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a solid chunk of iron

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the outer core

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molten iron

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mantle

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several different layers of molten rock:
-outter layers solid
-inner layers liquiod

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crust

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-outter layer of solid rock
-from 3 to 43 miles thick

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seismic shock waves

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speed and direction are effected by variations in:
-temperature
-pressure
-density
-composition of the materials of layers of the earth

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rock

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-assemblage of minerals in solid form
-most contain atleast 2 minerals
-the different combinations account for different rocks

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mineral

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-naturally inorgaic substance
-ususally having a definate chemical compositon

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how many minerals are unknown

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2,000

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metal

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-found in rocks
-inorganic
-malliable
-conduct electricity

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igneous rocks

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-formed directly from a liquiod state
-cover 1/3 of the earth

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molten rock bellow the earths surface

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magma

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once magma sqirts through the cracks it stops before it reaches the surface it creates

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-it cools slowly
-intrusive igneous rocks are formed
-more resistant to erosion

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magma appearing on the earths surface

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lava

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lava spreads around the earths surface...

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-and exposed to air and water
-extrusive igneous rocks are formed
-break down much more quickly

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three major categories of rocks

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-igneous
-metamorphic
-sedementary

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sedementary

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formed when rocks are broken down into smaller particles

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Sediment

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-can then be moved and spread out across the ground
-after being subjected to heat, pressure
and chemical processes
-These cover almost 2/3 of the earth

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Sedimentary rocks, frequently arranged in several horizontal layers

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called strata

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Clastic

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sediments consist of inorganic rock fragments. (sandstone)

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Chemical

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sediments are formed by the precipitation of mineral materials out of water. (gypsum)

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Organic sediments

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-produced from the remains of plants and animals
-Many associated with animal shells (like limestone).

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metamorphic rocks

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-are either igneous or sedimentary rocks that have been changed by some combination of heat and pressure
-(which can come from burial, fault movements, or contact with magma )
-These are by far the least prevalent of the three basic rock types
-they are usually associated with mountain building processes
-(EX: limestone can be changed into marble)

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Oceans currently cover

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71% of the earth

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The crust of continents consists of

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less dense materials than the crust making up the ocean floor

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Plate Tectonic Theory

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-In 1912, Alfred Wegener proposed Contiental drift as a theory
-clearly explains the location of volcanoes and earthquakes, the distribution of mountain ranges and other major structural features of the earth’s surface
-accounts for previously unexplainable distributions of certain fossils and glacial deposits
-helps clarify the geologic histories of the natural landscapes of the world

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continental shelf

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(shallow part of today’s ocean that used to be dry land during the most recent ice age).

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Alfred Wegener suggested

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-that all of the present continents originated some 225 million years ago as a single land mass called Pangaea
-which began drifting apart several million years later.

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Alfred Wegener was roundly criticized

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He was criticized because he could not explain the mechanism that caused the movement of crustal plates.

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By the 1960s, evidence began to mount that Alfred Wegener was...

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-probably right.
-(Ex: similar rocks, as well as plant & animal fossils in Africa and South America, and other issues)

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tectonic activity

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-refers to all forms of breaking & bending of the crust
-Comes from a Greek word meaning building.

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The major components of the Plate Tectonic theory are as follows:

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-The earth’s crust is comprised of several relatively rigid but fragmented plates
that move relative to one another by floating or gliding across the relatively
plastic mantle below. Some plates are huge & some relatively small.
-These plates generally move just inches per year.
-Earth scientists believe that heat currents in the earth’s interior are thought to drive plate movement.

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Divergent plate boundaries

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are where plates move apart from each other and magma moves up to take the place of the two plates that are separating.

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divergent plates

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-Geographically, these zones are usually located beneath the world’s oceans where the zone of divergence features not only spreading (sea floor spreading), but also vertical development
-The rifting episodes are infrequent in any one year, perhaps occurring only once every few hundred years. In any one year, however, rifting probably takes place somewhere along the length of the ocean ridge system
-since the thickness of ocean floor sediments increases with increasing distance from the rift itself, this indicates that those areas near the rift are geologically young
-ex:East Africa’s Rift Valley (extending north through the Red Sea)
The resulting fragmented trench is loaded with tall volcanoes (like Mount Kilimanjaro)

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transform plate boundries

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-(like the San Andreas Fault zone in California), are boundaries where plates slide past (usually with much friction) each other.
-Generally, there are no volcanoes along these boundaries, although earthquakes may be common.
-segments of divergent plate boundaries may experience much transform movement
-Los Angeles will rest along side San Francisco in 10 million years.

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convergent plate boundaries

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plate boundaries are where plates colide head on and this can produce two different results:
-Some head on collisions between plates of similar density result in mountains

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subduction

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-a denser oceanic plate runs into and dives under a less dense (continental) plate.
-leads to trenches off shore and volcanoes on shore

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Tectonic activity

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can be very subtle—the slow bending, twisting, and eventual cracking of large masses of rock.

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crustal movements

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only inches per year, takes many thousands of years to create significant landscape features.

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Folding

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-where rocks are bent;
-a large chunk of the earth’s surface that has been pushed together
-Heavily folded areas appear as a series of ridges and valleys
-ex:like in parts of Pennsylvania).

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Faulting

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-the cracking, breaking and fracturing of rocks under pressure
—frequently followed by movement (sometimes sudden) on either side of the fault

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characteristics of faults

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-Most major faults extend into the ground several miles deep
-they may or may not be clearly visible at the surface
-A single fault movement can result in slippage of as little as a fraction of an inch(or by as much as 50 feet).
-Repeated movement along a fault line can result in the development of large mountains with steep faces rising out of otherwise flat landscapes.
-Movements can happen annually or centuries apart, and they are frequently associated with earthquakes

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Earthquakes

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are the shaking & trembling of the earth’s surface associated with crustal movements. This includes crustal movement along deep cracks (faults) or volcanic activity.

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earthquakes are also closely associated with

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plate boundries
-95% are along the Pacific Rim, southern europe and southern asia
-But scientists still do not have a complete understanding of earthquake mechanics. For example, there are occasionally serious earthquakes far from plate boundaries

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Most earthquakes are

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-undetectable except by delicate instruments called sizemographs
-The movement detected is frequently called sizemic activity.

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The sudden movement of earth materials sends

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shock waves (seismic waves) through the earth (like ripples on a body of water).

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the further away you are from the
source

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the more that energy is dispersed over a large area, and the less likely you are to experience motion or damage.

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Magnitude

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is the word used to describe the shaking recorded at a particular place—and this is a function of both power, energy, and distance form the source.

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Endogenic system

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Internal processes that produce flows of heat and material energy from deep bellow the earth’s crust

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Exogenic system

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External processes that set into motion air, water, and ice (all powered by solar energy)

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Geologic time scale

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An effective device for organizing geologic time

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Geomagnetic reversal

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Patterns frozen in rock that help scientists figure out the story of the earth’s mobile crust

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Asthenosphere

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Aka plastic layer, contains pockets of increased heat from radio active decay and susceptible to slow convective currents

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Mohorovicic discontinuity

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Or Moho is the high velocity portion of the upper most mantle

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Continental crust

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Is made up of primarily granite

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Oceanic crust

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Is made up of primarily basalt

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The principle of Isostasy

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The principles of buoyancy and balance, explains the certain vertical movements of the crust

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Geologic cycle

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The model of external and internal interactions that shape the crust

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Rock cycle

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Describes the three principles of rock forming processes and the rocks they produce

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Intrusive igneous rocks form

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Plutons after it cools slowly in the crust and the largest pluton forms a batholiths

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When sedimentary rocks harden its called

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Lithification

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Sratigraphy

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The study of sequence, thickness, and spatial distribution of strata that yield clues to the age and origin of rocks

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Transform faults

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Along the offset of mid ocean ridges horizontal motions causes these faults

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Hot spots

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50 to 100 hot spots in the world

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Three types of plate boundaries

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Divergent, convergent, and transform

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Geothermal energy

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Literally refers to the heat from the earth’s interior

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Relief

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He vertical elevation difference on a landscape

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Anticline

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Along the ridge of the fold layers slope downward from the axis

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Syncline

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In the trough of a fold the layers slope downward toward the axis

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Graben

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Refers to the downward faulted blocks

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Orogenesis

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The birth of mountains

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Circum-Pacific belts

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Or the ring of fire, the region around the pacific that’s ha collision of continental plates

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Elastic rebound theory

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Describes the basic processes of the mechanics of fault breaks

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Pyroclastics

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Pulverized rock and clastic materials ejected during eruption

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Cinder cone

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Ejects pyroclastics from volcanoes

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Caldera

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A large basin caused by the collapse of volcano summits

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The focus is the

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point underground where the energy causing the earthquake is first released.

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the epicenter

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is the point on the earth’s surface directly above the focus of an earthquake.

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Although earthquakes can occasionally alter land forms, they are especially harmful to

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the structures we build. Fires from ruptured gas lines are particularly dangerous

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moment magnitude scale

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-Charles Richter developed a popular earthquake intensity scale
-his scale has been modified to account for a broader range of phenomena

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moment magnitude scale

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goes up to 9

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forcasting has proven even more problematic than

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for volcanic eruptions. Until plate tectonic theory of the 1960s

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A volcano

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is a mountain or vent in the earth through which flows molten rock and gas.

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Why does magma come up to the surface?

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“The density of magma is less than that of the rock from which it melts. Under the influence of gravity, the lighter molten material tends to rise . . .”

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80% of all active volcanoes are associated with the pacific ring of fire

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(Indonesia 127; Japan 77; Chile 75.)a huge zone of subduction.

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Several others volcanoes occur along zones of...bc...

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divergence (under the ocean—where intense pressure due to the weight of the water above prevents explosive eruptions).

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Active volcanoes have erupted in historic times

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dormant and extinct volcanoes last erupted much longer ago.

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In the United States,(volcanoes)

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The Cascade Mountains running from northern California, through Oregon, and into Washington have several volcanoes, Alaska's(including Mount St. Helens). And ? Aleutian Islands are a series of volcanoes.

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Although plate tectonic theory accounts for most volcanoes

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Hot Spot Theory accounts for the rest

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Hawaii

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rests in the middle of the Pacific plate-far from plate boundary.

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These islands are part of a long arc of arc

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-moving northwest to southeast
-from ocean floor to summit, they are the tallest volcanic mountains in the world.

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Islands at the northwest end of the chain are

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older and mor active (because they have been eroded a greater number of years)
-Kauai is 5 million years old,
-Oahu is between 2 to 3 million years old
-Big Island of Hawaii is less
than a million years old and

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Big Island of Hawaii

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is the only currently the only volcanic island.

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The Hawaiian islands are believed to have been formed

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by a cone of molten material that rises from the earth and punches a hole in crust as the plate moves northwest
-creates volcanoes over time.

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The Pacific Plate is moving about

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-10 cm per year (accounts for the spacing between islands).
-there is a new island forming to the southeast of the Big Island, is still well below sea level.

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(Hawaain islands) We are not certain what causes this

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plume of ? to appear at the same spot for millions of years (we think it has been going on for 80 million years.)

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Iceland is apparently

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a hot spot that straddles the [Mid Atlantic] ridge and has volcanoes of dual origin—both hot spot and mid-ocean ridge.” This might explain why Iceland is the only land above sea level along the Mid-Atlantic ridge.

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Eruptions featuring little gas

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are usually less explosive than eruptions featuring a larger % of gas (Mt. Saint Helens).

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If magma rises slowly

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there is greater opportunity for compressed gases to react to changed pressure and escape without generating a significant explosion On the other hand, when magma rises quickly to the surface, the rapid pressure change causes gases to expand suddenly leading to an violent eruption

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Viscosity

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is also an issue and this is frequently a function of magma temperature (most rocks melt between 800 and 1200 degrees C).

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Very hot magma (2200^c)is more liquid and less...

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viscus and its dissolved gases easily come out of solution when magma surfaces—therefore eruptions are less likely to be violent.

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Much cooler (1500^c) magma is much more...

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viscus. This inhibits the release of compressed gas which builds and frequently causes more violent explosions.

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In addition to lava, volcanoes produce...

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ash, steam, and large rock fragments (called tephra.)
-Occasionally, all of these materials may move down hill as a deadly pyroclastic flow.

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Eruptions can be brief but...

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they may also last (off and on) for decades at a time.

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During an explosion, large areas may become blanketed with thick layers of

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ash
-which may become a mudslide after a heavy rain.

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Forecasting volcanic eruptions are

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difficult
-geo-scientists can obtain data that help them accurately predict an eruption.
-But other times, violent eruptions provide no absolutely no warning

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Weathering is the combined action of...

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physical, mechanical, and chemical processes that break down rocks.
-The term weathering suggests that “the weather” produces the elements and circumstances that make big rocks into little rocks.
-Weathering is essential in producing soil

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Physical or mechanical weathering reduces

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rocks without changing their chemical composition.

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Tectonic forces and rapid cooling cause

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joint and fracture formation. These cracks create more avenues for joint and fracture formation for weathering agents to continue the process.

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Frost wedging occurs when

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water makes its way into joints or fractures in rocks—and then freezes. The expanding ice can produce up to 1,400 pounds per square inch of pressure, which is frequently enough to shatter otherwise solid objects. This is important in places where freezing and thawing temperatures occur?

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Salt crystal growth plays a similar role in

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dry environments where high rates of evaporation leave behind salts to collect in cracks. As these crystals grow, they have the same effect as ice.

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tree roots eventually

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crack rocks in many places—check out any old sidewalk!

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Chemical weathering causes changes

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in the chemical structure of the rock. Water is usually involved.

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Hydrolysis is more than the mere

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wetting of rocks; it is the permanent chemical combination of materials with water producing a new chemical structure which is frequently less resistant to weathering.

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Oxidation

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involves the chemical combination of minerals with oxygen. Metals in rocks and soil literally “rust” and leave rocks easier to break down

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Solution

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occurs when certain materials literally disolve in water (water can disolve far more than just salt or sugar!). Because water can dissolve carbon dioxide, even “pure” rainwater is a mild form of carbonic acid

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The carbon in this water can combine

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-with certain materials (called carbonation)
-that can then be dissolved and carried away.
-(Limestone and marble are especially sensitive.)

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Since chemical weathering operates best

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in warm temperatures where water is present, warm and rainy climates are especially vulnerable to chemical weathering. Also, chemical processes break down rocks much faster

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(karst topography)The distinctive

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surface features, which are the direct and indirect result of solution by water

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(karst topography)Karst landscapes are most often found in

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-humid places
-limestone underneath, which is easily disolved

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(karst topography)Water sinks into the ground, and

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after carbonation/solution, empty caverns are left behind.

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(karst topography)Some of these caverns

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-they can collapse without warning creating a sink hole.
-some small, some are more than 100 feet deep
-may turn into lakes if the base is below the water table

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(karst topography)Indeed, florida is one of the

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leading places in the U.S.

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(karst topography)a more mature karst landscape would

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feature mounds of material that had not been dissolved.

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mass movement

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Gravity is an important force; and the down slope movement of surface material by gravity

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The accumulation of soil

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disturbance that takes place over time makes gravity more effective

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The concept of angle of repose

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is used to describe the steepest angle that something can endure before falling. The exact value depends on the type of material and the condition of the surface

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Slow mass movements are generally

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imperceptible.
-They may take days, weeks or even years to happen
-they are more prevalent and they move more material than more rapid mass movements.

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Earth flows and slumping move

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significant chunks of hillsides. They occur primarily in humid environments that become saturated.

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Soil creep

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occurs on practically all slopes with soil.

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Rapid mass movements are characterized

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-by perceptible movements of materials.
-They are usually brief and potentially dangerous
—they may be locally significant
—they are not shapers of large portions of the earth’s surface
-Part of this is because they occur in hilly or mountainous places.

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mudslides

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are the most fluid of major types of land movement.
-often an arid climate phenomena and usually triggered by heavy
-generally long and narrow, frequently occurring in or around dry riverbeds.
-in humid environments, deposits of volcanic ash may combine with heavy rain or ? may clear a region of vegetation that might otherwise hold ? and other materials after a heavy ?

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Rock or land slides—

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the general term for all other forms of rapid debris flow.

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Many geographers study dirt because

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soils of different properties are produced in different places

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(Soil composition)Minerals or Inorganic material

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comes from weathered rock.

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(Soil composition)All soils have at least some

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water even if it is nothing more than a microscopic layer around each grain.
-important bc this is what disolves the minerals that plants depend on.

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(Soil composition)All soils (except those saturated by water)

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contain air
-enough for plants, small animals,
and microorganisms to breathe.
-This is why water logging soils kills most plants.

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(Soil composition)Organic material comes from

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both decomposing plant and animal material as well as living organisms.
-much of it is microscopic.

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Organic material

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-Most soils are less than 5% organic material although peat soils may be well over half organic

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Humus

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(partially decomposed plant remains)
-is a source of nutrients to living plants.
-humus increases a soil’s water retention capacity.
-Humus also adds structure to a soil—helping it resist errosion

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Soil is a complex, dynamic...

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material in which physical, chemical, and biological activity occurs.
-The solids, liquids, and gases all cycle through the soil, producing a nearly constantly evolving system

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A soil’s

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color provides clues as to its composition.
-For example, reddish hues usually indicate the presence of iron in the soil
-deep brown or black hues frequently indicate high percentages of organic matter

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Soil texture

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deals with the size of mineral particles. The scale runs from extremely coarse materials to fine material.

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(Soil texture) gravel particles over

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2 mm in diameter(large)
-(this extremely coarse material is generally not considered soil).

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(Soil texture) Sand particles are from

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.05 to 2 mm in diameter (these are relatively coarse; even fine sands are more course than the next smallest group).

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(Soil texture)Silt particles are from

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.05 to .002 mm in diameter (Very small, medium texture).

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(Soil texture). Clay particles are smaller than

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.002 mm in diameter (very very smal, fine textured materials).

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(Soil texture)Most soils have some combination

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of all three size particles; loam: soils that have relatively even percentages of all three

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(Soil texture)A soil’s ability to

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-retain water is determined (at least in part) by its texture.
-Organic materials also help soils retain water.

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Sandy soils allow

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water to move through them too quickly
-may require irrigation to cultivate.

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Fine textured soils

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-prevent the movement of water through them.
-clays prevent water from penetrating to deeper layers

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Loams occupy

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-distribution of all three soil types
-are prefered for agriculture.

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Structure

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how well a soil clumps.

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Three things that provide soil structure

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-Organic materials
-moisture
-texture

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Soil structure helps prevent

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errosion

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Coarse textured soils without organic material have little

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structure
-they fall apart when wet

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Very fine textured materials with organic materials may have

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too much structure and be too hard

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Although similar soils may extend horizontally for miles, almost all

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soils show changes just a few feet below

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Soil profiles are

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vertical slices of soils, a collection of horizontal layers

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Generally there are ...well defined horizons in each soil, and...

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5-6 /and these horizons differ in physical, chemical and biological characteristics.
-For example, most biological activity is within the top foot or two.

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(Soil developement)Parent material is the

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inorgainic material that forms the basis of most soils.

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(Soil developement)Parent material...In some cases/ In other cases

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-residual materials (parent materials from underlying bedrock) dominate a soil./
transported materials may have originated from away and then been deposited.

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(Soil developement)Relief

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is the vertical characterization of a landscape

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(Soil developement)-Relief, Soils on

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-steep slopes tend to be thinner and consist of more coarse material because they are easily eroded
-more likely to be dry bc course texture allows moisture to escape.

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(Soil developement)-Relief, Soils in flatter places tend to be

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thicker and much better developed.

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(Soil developement)-Relief, Depressions on the landscape

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are more likely to have waterlogged soils because they are the destination for many fine textured materials
-(that block water movement).

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Microbes or bacteria

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-the most numerous in almost any healthy soil.
-one million per cubic centimeter

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Microbes produce

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organic acids that break down parent material creating more soil.

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Some microbe bacteria help

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decompose dead plants and animals.

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microbe still others inhabit the roots of

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legumes (soybeans, alfalfa, peas and so forth) and it is here that they perform the vital task of converting atmospheric nitrogen into a form that plants can use. This is called nitrogen fixation.

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Other vascular plants perform several functions...

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-They help prevent soil errosion after heavy rain.
-plants die and serve as a source of nutirent for living plants.
-Finally, trees with deep roots literally pump nutrients from deep layers in the soil up to the surface where they can be recycled as leaf litter.

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Up to a __________ earthworm may inhabit a single acre.

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1 million

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earthworms they aerate the soil with

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constant air holes

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earthworm feces also improve soil

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quality by ingesting and excreting minerals in a form that plants can use.

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Climate impacts soil in 3 ways

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-Excessive precipitation may cause leaching of important minerals beyond the root zones of many plants.
-In dry places, excessive evaporation may leave behind so many dissolved minerals over time that soils become salty climates frequently have more acid soils because cool weather retards the decomposition of organic materials.

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Soil can be thought of as

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a renewable resource because it accumulates over time

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(Soil) In warm moist regions, almost 1 centimeter of

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1 cm soil can form each year.

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(Soil) Yet in dry regions it may take 1000 years to produce

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30 cm of new soil

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As with climate, soils have been divided into several types and soil maps reflecting the

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variety of different soil types have been produced for most counties in the United States.

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Denudation

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Tearing down the land, involving weathering, mass movement, erosion, transportation, and deposition

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differential weathering

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different rocks offer different resistance to weathering and produce patterns on the landscape