Outline of Earth Science - Part III
Weathering is defined in two ways
- the physical and chemical processes which decompose rocks and convert them to loose gravel, sand, clay, ions and soil precursors
- an appearance of materials which have begun to decompose.
Erosional processes pick up and carry away particles and ions. The agents of erosion are from strongest to weakest in terms of particle size:
Processes of physical weathering include:
- Pressure-release fracturing causes exfoliation or jointing.
- Wave action causes rock fall and landslides by oceans.
- Frost wedging produces talus.
- Lightning strikes crack rocks.
- Fires can fracture rocks when water inside explodes into steam.
- Abrasion by gravity, ice, water or wind leaves characteristic shapes.
- Organic effects include "desert varnish," roots and animal activity.
- Thermal expansion and contraction may be invisible but effective: size changes as a substance goes from solid to liquid to gas. Substances changing size often break.
- Plate tectonic effects include faulting, slumping and sliding.
Chemical Weathering -- quartz is mostly resistant to these processes.
Physical and Chemical Weathering work together.
- Acids have more Hydrogen ions (H+), bases have Hydroxyl ions (OH-).
- The pH scale measures relative concentration of Hydrogen ions
- Low numbers (0 - 7) are acids; high pH (7 - 14) are bases
- Always add ACIDS to bases.
- There is no pure water in nature, distilling or deionizing it results in vapor or steam.
- All rain is slightly acid because water falling through air reacts with carbon dioxide to produce carbonic acid:
CO2 plus H20 ---- H2CO3
- Increasing acidity increases erosion by more dissolution, but also because clays stay in suspension in even slightly acid waters. Areas with limestone road base and building facings suffer more from acid rain.
- Water can be more basic than ordinary. Calcareous springs and seeps as well as limestone bedrock tends to make groundwater basic. Limestones and other carbonates fizz when acid applied.
- Ions deposit when conditions change. This often occurs at the air/water interface or at a pressure boundary. Ions precipitate to form cements in sediments and form stalactites and stalagmites in caves, petrified wood and chert and geodes.
- Hydrolysis -- Water reacts with a mineral and forms a new mineral with water in the structure. For example, feldspars/micas hydrolyze to clays.
- Oxidation -- Reaction with atmospheric oxygen changes some minerals. Iron rusts and sulfide deposits exposed oxidize and release sulfuric acid (H2SO4).
- Salt cracking occurs when salt crystals in rocks expand and crack rock.
- Exfoliation results from thin plates of rock peeling off and falling.
|The type of weathering influences the sediments formed:
|soluble salts/soluble silica
|soluble Fe+ and Mg+ ions
Surface Waters .
The rock parent material of soil is called regolith. Soil is composed of regolith, organic materials, air and water. Certain nutrients are essential for plant growth. An organic rich layer (A-Horizon) usually overlays depleted subsoils (B-Horizon) which, in turn, overlay parent material or broken rock (C-Horizon). An average soil is composed of 25% air, 25% water, 45% rock fragments and 5% organic materials.
Soil forming factors include:
- Parent rock
- Climate - both wet and dry affects soils
- capillary action produces pedocals and caliche soils by the leaching of ions like Ca+ and Fe+
- salinization occurs in areas overwatered and in deforested laterites (high Aluminum soils typical of tropical forest ares) as well as by evaporation on natural saline playas
- high rainfall produces - pedalfers (Al- & Fe+)
- high temperature and high rainfall produces laterites (iron oxide produces the red color) and bauxites (Al ore)
- Time of formation
- Biotic factors
- Slope face and angle
|Plant growth rates are dependent on
|source of air masses/prevailing winds
|insolation and sun angle/duration
|steepness and elevation
|water runoff speed increases erosion
higher elevations tend to be colder
|mineral and organics supply
|age of soils
amount of decaying matter in system
|amounts of 02, CO2 and other atmospheric gases have changed greatly over time
IL soils 15,000 years old
Australian soils have been forming for millions of years
Soil Erosion and Transport occurs by the agents of erosion
- Gravity -- landslides
- Streams -- ex. annual Nile inundation and deltas
- Glaciers -- Illinois soils
- Wind -- some wind deposits are called loess, say "luss"
- Trail erosion -- due to compaction
Mass Wasting = erosion by gravity
- Force of gravity = 9.8 m/s2 = 32 ft/s2
- Slope Angle (angle of repose)
- Type of Rock
- Orientation of Rock Layers
- Nature of Unconsolidated Materials (angle of repose)
- Water and Vegetation
- Earthquakes and volcanos
Types of Mass Wasting
- Slump - blocks of materials move together
- Rockslide or Rock Avalanche)
- Debris flow
Surface Waters .
Fresh Water: Streams, Lakes, Ground Water and Wetlands
- The Hydrosphere is all the water on earth.
- The hydrologic cycle moves water through the various parts of the system
- Streams are any body of water flowing in a channel.
- Rivers are large streams; tributaries feed rivers.
Stream Flow and Velocity is based on three factors
- Gradient = rise/run = steepness of stream
- Discharge = amount of water flowing in stream
- Channel characteristics of the bed and banks
Streams transport sediments.
- Carrying capacity of stream = competence = biggest particle the stream can carry
- High energy streams carry more sediment than low energy streams.
- Dissolved Load - carried as ions
- dependent on discharge and chemistry, not velocity
- less than 20 percent of total sed. load
- bed load
- planar flow
- cross bedding
- suspended load
- acid waters keep clays in suspension
Base level and downcutting
- Downcutting occurs when streams erode channels downward trying to reach base level.
- Natural and man made dams change the base level. A Chicago example is waterfall at Argyle and Francisco in the Chicago River. So base level can be changed by damming or by draining.
- Water stored behind dams has potential energy. Water released through sluices or waterwheels converts that to kinetic energy.
- The sea is the ultimate base level.
- High gradient streams downcut more rapidly than low gradient streams.
- Streams make v-shaped valleys.
- As velocity drops, particles fall out of the stream.
- Low gradient streams cause lateral erosion and flow in looping meanders.
- Low gradient streams are often "braided."
- High gradient streams have higher erosion.
- When steep streams arrive in flatter lands which drain alluvial fans form.
- Any stream arriving at a body of water constructs a delta.
Flow is the amount of water moving.
- Sheet flow is where water flows directly on the surface.
- Stream flow is where water flows within banks.
- turbulent flow - water moves erratically - ex. white water
- laminar flow - water flows relatively straight. Maximum velocity is at center, curving channels result in side to side transfer of velocity flow. Cut banks, point bars and natural levees are the result of laminar flow.
Drainage basins occur where major rivers flow together and are separated from other drainage basins by "divides." Other drainage basins include the Amazon, the Congo and the Ganges rivers.
|Drainage creates seven patterns of topography.
|Cause or Location
|flat-lying rocks with uniform reaction to erosion
|flows in joints in the rocks
|tributaries at right angles to main streams
|found in folded topography
|closely aligned streams
|flow on steep slopes or parallel landforms
|all flow from central point
|volcanos, kames, dump piles
|all flow to a central point
|calderas, sinkholes, craters
|glaciation, massive earthquakes, uplift or downdropping
Erosion and uplift produce landscapes
- Downcutting by streams flattens mountains and widens floodplains and
- Uplift and movement by tectonic forces raises/lowers landscapes at the same time.
- It is the combination of the two which makes the final landscape.
Flooding occurs when more water arrives than the channel or flood plain can hold. The stream runs over its banks and we call it a "flood." They can be due to:
- Amount of rainfall (too much in too short a time) for example the annual historic floods of the Nile and the 1993 Mississippi Floods.
- Outflow of lakes, levees and dammed structures.
- Displacement of landslide/ice debris into lakes and dammed structures.
- Downdropping in earthquakes.
Floodplains are lands which are covered by floods. Rivers historically flowed free and permanent structures built on floodplains were traditionally ephemeral. Egyptian temples which have survived the ages were built outside the traditional Nile floodplain.
Sorting reveals the different types of flowing/standing water structures.
- Confined sorting - like sediments in a bottle or puddle
- Unconfined sorting - flow in streams and channels, shoreline deposits
- Unsorted - material dumped by glaciers and the works of man.
Levees and Channels.
- Channels and levees are formed both naturally and erected by man.
- Man-made channels and levees are usually straight to flow faster and restrict shipping less.
Samuel Clemens (Mark Twain) must have had a good geology teacher. In "Life on the Mississippi" (1863) he wrote: "One who knows the MS [knows]... that ten thousand River Commissions with the mines of the world at their back, cannot tame that lawless stream, cannot curb it or confine it, cannot say to it, "Go here," or "Go there," and make it obey; cannot save a shore which it has sentenced; cannot bar its path with an obstruction which it will not tear down, dance over, and laugh at... one would ... say the Commission might as well bully the comets in their courses and undertake to make them behave, as try to bully the Mississippi into right and reasonable conduct."
Lakes are large inland bodies of standing water which occupy low topography.
- Lake margins are defined by one elevation (contour line).
- Lakes are natural and man-made.
- Lakes occupy artificial base levels and contain potential energy.
- Outflow or overflow of lakes can be catastrophic.
- Lakes tend to silt up, become boggy and eventually die. Volo Bog in Lake County is a local example of a silted up bog.
- Glaciers are responsible for a large number of lakes in the Chicago area.
- Lakes form in volcanic craters.
- Oxbow lakes result when a loop of a stream silts up and becomes a lake.
- Pull-apart basins can contain lakes like Lake Baikal and the man-made Salton Sea on the San Andreas in southern California and Reelfoot Lake along the Mississippi River.
Types of lakes:
- Oligotrophic, deep lakes tend to have nutrients at the bottom - where it is too dark for photosynthesis, support few, large animals and have a dark blue or clear appearance.
- Eutrophic shallow lakes have the nutrients where the bottom feeders can get to them and tend to become covered with green scum, Spyrogyra, and other plankton. As the plants consume all the oxygen, fish and animals with oxygen dependent life styles cannot persist. Addition of sewerage, fertilizer runoff and other nutrients to flowing water will increase available nutrient and can cause eutrophication.
- Freshwater lakes include Lake Michigan, and the rest of the Great Lakes (can you name them?), many smaller lakes including Chain of Lakes, Devils Lake, Wolf Lake and Lake Calumet in the Chicago area. Freshwater lakes may be supplied by rain water or ground water.
- Saltwater lakes include Utah's Great Salt Lake, the Bonneville Salt Flats (famous from thousands of car commercials and the Dead Sea which collects in the Dead Sea fault along which the Jordan River also flows. The salt arrives from eroding rock formations surrounding the lakes.
- The temperature of the top water and bottom water in lakes may be different and change on a seasonal basis. Local climate results in lake overturning. Volcanic lakes full of toxic gases can also overturn resulting in loss of life in surrounding areas.
Surface Waters .
|Three factors control fluid flow underground
|the amount of void space in the rock or sediment
|the way that void space is connected
|underground fluids flow from high pressure to low pressure
Ground water is found below the surface of the ground. If you dig a hole along the \ beach, you will find water closest to the surface when you are nearest the water - and farther away as you go upbeach.
- The dry layer on top is called the unsaturated zone (zone of aeration/vadose zone)
- The wet layer below is called the saturated zone (phreatic zone).
- The water table is the top of the saturated zone.
- People (and other organisms) dig wells to reach the ground water.
- Caverns and sinkholes form in karst topography when weaker rocks are removed by acid groundwater and other underground fluids.
- Hot springs, geysers and geothermal energy are produced where groundwater reaches hot magma. "Black smokers" and other midocean vents are responsible for much mineral deposition.
- Rain or surface water may recharge groundwater, or groundwater may recharge streams and lakes.
- Where the water table intersects the land surface, "springs" bring ground water out onto the surface.
- Impermeable rock layers ("aquicludes") can prevent the downward migration of water; perched ponds or perched water tables result.
- Saline waters may occur below freshwater. Continued pumping results in a saline well.
- Removing groundwater from sediments or rocks may result in subsidence of the ground.
Two categories of Aquifers, "water bearing" layers of sediment or rock.
- Unconfined aquifers include the top layer of the ground water and any other groundwater layer which needs pumping to produce water.
- Two aquicludes surrounding and aquifer form an "artesian aquifer." This type of aquifer will produce water without pumping due to the head pressure of the water in the formation itself. This is the type of oil formation which produces "gushers."
Wetlands interact with groundwater in many ways. They may be perched on an aquiclude, fed by groundwater springs, dammed by surficial topography and feeding groundwater, and so on. Each form leaves a characteristic deposit.
Surface Waters .
Glaciers are large masses of compacted snow and ice. They form:
- by converting snow to ice to "firn" to glacial ice
- when accumulation exceeds ablation (melting).
Controls on glacial growth and movement include:
- Slope angle and face
- Insolation amount and angle
- Regional airmasses
- Other local or regional factors
Glaciers are divided into two categories based on topography:
- Alpine glaciers which occur in mountains.
- Continental glaciers, ice caps, ice shelves and ice sheets which occur on depressed landmasses.
And are also divided by temperature into:
- Warm glaciers where water can and does flow, and
- Cold glaciers where free-flowing water is rare or nonexistent.
Glaciers move material by:
- Basal slip causes whole glacier to slip forward
- Plastic flow results from snow moving within the glacier down the gravity gradient.
- Irregular ground topography results in the glacier forming crevasses, loose blocks and ice falls.
- Surges and avalanches can move large amounts of material quickly.
Speed of glacial movement depends on
- Angle of land below glacier
- Thickness of glacier
- Antartica movement of about 2 meters per day has been recorded
- Historic glaciers of Illinois moved an average of 2 centimeters per month.
|There are four glacial environments
|Lakes, soil, forests, ice, moraines
|Crevasses, water flows, drumlins and caverns
|Compressed sediments, flowing rivers
|in front of
|Lakes or highly eroded landscapes depending on angle of land
Underlying topography may exert an influence on glacial topography.
- Where ice is bent, undercut or suddenly unconstrained, crevasses may form.
- Where the land rises up, the ice may be constrained and possibly melted by insolative gain from the exposed land surface.
- Where the land meets a lake or the sea, ice sheets may form over the water forming ice shelves which calve off icebergs and floes.
- The snow line separates the accumulation zone from the ablation zone. It can be imaged on satellite photos and measured from year to year to measure the health of the glacier.
- Tributary glaciers feed into main glaciers.
Glaciers carve landforms by erosion.
- Loose rock is plucked and carried, possibly causing striations to underlying rock.
- Alpine glaciers slowly carve
- horns, ex. The Matterhorn ("the mother of all horns") in Switzerland.
- cirques and
- truncated spurs.
- After melting, tarn and pater noster lakes may form in old cirques, hanging valleys and plunging waterfalls reveal the path of tributaries.
- Glaciers carve U-shaped valleys like Yosemite in California.
- If the valleys are flooded by the sea, we call them "fjords." The Hudson River Valley up to the Tappan Zee Bridge is a fjord.
- Deep gouges caused by continental glaciers fill with water and produce deep lakes like NY Finger Lakes and the midcontinental Great Lakes.
Glacial deposits ("drift") are divided into two categories:
A.) Till -- deposited directly from the ice.
- Moraines form from unsorted rock debris carried along by the glacier.
- lateral moraines define the melting edge at the side of glacier.
- medial moraines form where two glaciers flow together.
- terminal moraines (end moraines) show where the glacier melted and are unsorted.
- ground moraines are unsorted, thin layers laid in a rapid retreat.
- extrusion moraines are caused by the weight of ice squeezing sediments out.
- Erratics are loose boulders which may have been transported a long way from their parent rock. We use them to mark the ends of driveways.
B.) Stratified Drift -- carried by the ice and then reshaped by water sorted either confined or unconfined. This produces various landforms.
- Braided streams form when vast amounts of sediment arrive at a flat-lying landscape.
- Valley train deposits occur when a river flows between two ice lobes.
- Outwash plains form as water flows away from a glacier and is not captured by a lake.
- Kames formed by sediments which fell down a crevasse. When the water melted, a conical hill remains.
- Eskers are the remains of subglacial rivers
- Kettle lakes form when icebergs are buried in the till and melt, leaving a lake.
- Drumlins seem to form from unconsolidated material caught in a flow beneath a floating block.
Surface Waters .
A desert is any region that receives too little rain and too much sun, produces too little vegetation, or is too cold to support a human population.
Classification of deserts
- Some authors have divided "steppe" for an environment that is too cold and too dry, while reserving "desert" for a place that is too hot and too dry. This totally overlooks places like Antarctica's Dry Valleys which are both too cold and too dry.
- Others divide deserts into low latitude between the tropics of Cancer and Capricorn, mid-latitude deserts from there to about 60 degrees north or south latitude and high-latitude deserts.
Climate plays a role in the formation and maintenance of deserts.
- Latitude - equatorial and polar are extreme, but deserts today are concentrated around 30 degrees north.
- Falling air contributes to deserts at 30 north and south latitudes.
- Rain shadow deserts -- mountains block wet air; lee side is dry. An American example is wet Pacific Northwest and upper California and dry Nevada.
- Coastal and interior deserts include the Atacama and the Gobi desert.
Water and Deserts
- Desert streams are also called "washes" and "arroyos" and flow in areas that look like pavements or roads to people unfamiliar with the habitat.
- Desert lakes are called "playa lakes" and if dry, the bed is called a "playa." It is "Plain" in Spanish; so the rain in Spain actually falls on a playa - not a plain. :)
- Commercial minerals including salt, borax, nahcolite and trona are harvested from dried playas. The Great Salt Lake is an example of this type of habitat.
- Flash floods occur in both arroyos and canyons.
- Bajadas form from merging alluvial fans extending into desert valleys.
- Pediments are sloping surfaces eroded into the bedrock.
- Desertification is the process of becoming a desert. Grazing, loss of plant cover, changes in climate, moisture and salinity all play a role in the process.
Wind in deserts
- Wind erosion and desert pavement
- Aeolian transport (by wind)
- angle of repose
- slip face
- fossil dunes
- Loess ("luss") is windblown silt, near vertical angle of repose
|Four types of dunes
|Type of Dune
|rocky deserts little sand
|curved - tips point away from wind
|even sand and lots of it
|straight or wavy - perpendicular to wind
| dune in plants
|curved - tips point into wind
|wind direction erratic but prevailing, limited sand
|long nearly straight dunes parallel to prevailing wind.
Surface Waters .