APES Unit 4


Unit 4.1 Plate Tectonics

Three types of Plate Boundaries: 

  • Convergent - plates here push toward each other, which typically causes volcanoes

    • Releases magma

    • May cause earthquakes  

  • Divergent - plates here push away from each other, tend to have ridges

    • Mantle starts to push up, which could cause a mountain or volcano

    • Typically causes sea floor spreading

    • May causes earthquakes less frequently 

  • Transform - also known as the strike/slip boundary

    • Plates here slide past each other

    • No ridges or volcanoes

    • Tends to have shallow earthquakes, more frequent 

Plate Boundaries

  • Earth is made of layers:

    • Lithosphere (crust)

    • Asthenosphere (upper mantle)

    • Mesosphere (lower mantle)

  • Plates are the less dense upper part of the crust floating on the denser lower portion

  • Where are the Plate Boundaries?

    • There is a North American plate, South American plate, Pacific Plate, African plate, Eurasian plate, Nazca plate, Indo-Australian plate, Antarctic plate, Philippine plate, and Juan de Fuca plate

    • Plate boundaries vary globally

      • Plates are moving in all directions 

      • Each plate may have all 3 different plate boundaries

      • Recall that the movement of the plates can determine geologic features at the boundary

      • Type of plate, Continental or oceanic, also plays a factor in the feature 

  • Geologic events help identify plates 

    • Example: earthquakes, volcanoes, hot spots 

Convergent and Divergent Boundaries

  • Plates can have multiple boundary types

  • Continental plates are less dense, so “float” higher

  • This can lead to several formations such as:

    • Volcanoes

    • Island arcs

    • Earthquakes

    • Hot spots

    • Faults

Earthquake Formation

  • Earthquakes occur at a plate boundary and/or fault line

  • Fault lines lock up - building up stress/energy

  • Energy releases, causing an earthquake

Tectonic Plate Consequences 

  • Plates can have breaks in their surface, leading to volcanic island chains

    • Japan

    • Indonesia

    • Hawaii

  • Tsunamis

    • Typically caused by earthquakes

    • Long sea wave, can also be caused by underwater landslides

    • Ecological Consequences:

      • Destroys habitats 

      • Drowns species

      • Uproots trees

      • Contaminates water with saltwater and debris 


Unit 4.2: Soil Formation and Erosion

  • Soil is formed when parent material is weathered, transported and deposited 

    • Parent Material - original rocks that were broken down to form the basis of the soil

    • Weathering - the mechanical breakdown of rock

  • Factors that go into Soil Formation:

    • Type of Parent Material - rocks are broken down by wind and rain, soil tends to retain basic chemistry of these rock

    • Climate - average temperature and moisture change rate of weathering and leaching (nutrients in water), with redistribution as well

    • Topography - slope of the land may affect erosion

    • Biological Factors - plants, animals, microorganisms

    • Time - soil formation is continuous, there’s no end

  • Soil Profile (Soil Horizons)

    • Over time, soil layers build up and form common layers

    • These are known as soil horizons, or a soil profile

      • Materials/Layers:

        • Organic Matter 

        • Surface Horizon

        • Subsoil

        • Substrat

  • Soil Erosion

    • Over time, soil erodes due to several factors:

      • Water

      • Wind

      • Gravity

      • Human factors 

        • Leads to water contamination 

    • Human Factors of Soil Erosion

      • First problem - Deforestation 

        • The lack of roots holding down soil; are often replaced with plants that worsen erosion, examples include soybeans and wheat

      • Second problem - Overgrazing 

        • Pastureland can lead to cattle overeating and the top layer of soil can erode with wind and rain

      • Third problem - Pesticides and Fertilizers 

        • These can change chemistry of soil and kill microorganisms in soil

      • Fourth Problem - Tilage practices 

        • Turning and breaking up soil keeps top layer from accumulating organic material and roots

Erosion of Soil into Water 


Types of Erosion into Water

Solution to this Type of Erosion

Sheet Erosion - surface layer is removed by water

Maintain plant cover

Rill Erosion - small channels of water flow

Strip cropping or contour plowing

Gully Erosion - wider cuts from expanded rill erosion

Divert water away from rills and gullies


Erosion’s Effects on Watersheds

  • USDA Study on Watersheds

    • Study on thousands of watersheds

    • Public and private lands

    • Farm fields all over US

    • Sheet and Rill erosion


Unit 4.3: Soil Composition and Properties

Soil Texture Makeup:

  • Sand - 2 mm to 0.05 mm in size

  • Silt - 0.05 mm to 0.002mm in size

  • Clay - smaller than 0.002 mm in size

    • Most soils are typically a combination of all three

Water Holding Capacity 

  • Larger particle size allows water to pas through (sand)

  • Smaller particle size doesn’t allow water to pass through (clay)

Measuring Soil Composition 

  • Soil composition can be determined by percentages. 

  • Knowing the percentage of sand, the percentage of silt, and the percentage of clay can determine soil type.

  • The slip triangle is used to determine the type of soil.

    • It’s not necessary to memorize all the soil combinations or types, but it is necessary to memorize the soil triangle

Soil Tests

  • Variety of Soil Assessments:

    • Chemical

      • Nitrogen (nitrates)

      • Phosphorus (phosphates)

      • pH (acidity)

    • Physical 

      • Soil composition 

      • Water holding capacity

    • Biological

      • Earthworms

      • Bacteria 

  • Chemical Tests

    • Allow for plants and animals to thrive in soil 

    • Addition of fertilizers can increase nutrients N, P, and K

    • Some fertilizers and increased rainfall can also increase acidity 

  • Physical Tests

    • Soil composition - percentage of sand, silt, and clay

      • Sand = 20/31 x 100 = about 65 percent 

      • Silt = 9/31 x 100 = 29 percent

      • Clay = 2/31 x 100 = 6 percent

    • Determining the amount of these will affect percolation and infiltration 

      • Percolation - movement of water into ground

      • Infiltration - movement of ions or chemicals through percolation

  • Biological Tests

    • Soil is not inert: 

      • Bacteria

      • Archaea

      • Fungi

      • Earthworms

      • Burrowing animals


Unit 4.4: Earth’s Atmosphere

Composition of the Atmosphere 

  • The atmosphere is a mix of different gasses:

    • Nitrogen - 78%

    • Oxygen - 21%

    • Trace Gasses - 1%

    • (Ar, CO2, Ne, He, CH4, Kr, H2, H2O)

  • Layers of the Atmosphere 

    • Atmosphere is a blanket of air covering the Earth from the ground up

      • Exosphere (600-10,000 km)

      • Thermosphere (85-600 km)

      • Mesosphere (50-85 km)

      • Stratosphere (20-50 km)

      • Troposphere (0 to 6-20 km)

        • Varies depending on location

  • Temperature Changes in the Atmospheric Layers

    • Air is most dense near surface, temperature decreases at the top of the troposphere to tropopause

    • Stratosphere has a rise in temperature with ozone (O3) formation

    • Mesosphere temperature drops again due to thinning atmosphere 

    • Thermosphere receives UV and X-ray radiation, so temp rises, still extremely thin air


Unit 4.5: Global Wind Patterns

  • The Earth’s atmosphere is held by gravity

  • As the Earth rotates, the air circulates 

  • The heating and cooling changes the density of the air as it moves, due to convection 

The Coriolanus Effect

  • Along with heat, rotation of the Earth deflects the wind as well. 

Predictably of Wind Patterns

  • The exchange of heat and a orioles effect leads to patterns that are generally regular

  • Ecosystems around the globe result from these exchanges of heat and rotation


Unit 4.6: Watersheds

General Watersheds 

  • Watersheds - the highest point (also called a divide) of a river

    • Tributary - small rivers leading to larger rivers

    • Delta - where the small river meets the large body of water for the larger river 

    • Source Zone - head of the river

    • Transition Zone - between the head waters, cold water with a lot of oxygen

    • Floodplain Zone - river spreads out, water is warmer and has less oxygen

    • Rivers flow because of gravity - flow from the highest point to the lowest point

Rivers when it Rains

  • Rainwater that lands within the watersheds does one of two things:

    • Runs downhill across the land associated with the watershed until it joins the river or one of its tributaries 

    • Percolates through the soil to join groundwater 

  • Rainwater that lands at the divide between watersheds will run into either one watershed or the other

Specific Watershed

  • Note the following in watersheds:

    • Area

    • Vegetation

    • Type of soil that most likely supports the vegetation 

    • Slope of watershed

Watershed Affected by Human Action

  • Logging - cutting down trees, removing roots that hold soil that can rush sediments into water when it rains

  • Residential - pesticide use, can wash into rivers when it rains

  • Industrial - waste and pollution, can easily end up in rivers

  • City - any waste in the city can easily roll off concrete and into the river 

  • Livestock/Cropland - animal waste, can end up in rivers

  • Dam - block the flow of sediments that are necessary for other organisms that receive them via river flow


Unit 4.7: Solar Radiation and Earth’s Season

  • Insolation - incoming solar radiation

    • Insolation = solar radiation / area

  • Insolation change due to shape of earth

    • The surface most perpendicular to the sun will have the highest concentration of solar radiation per unit area (highest Insolation)

    • The angle of incidence decreases moving towards the poles, increasing are of incidence, which in turn lowers Insolation 

  • Insolation varies with unit area

  • Solar radiation is constant

  • The angle of incidence for the Sun’s energy varies because of the spherical shape of the Earth

  • A smaller angle of incidence leads to a larger area over which the solar radiation is spread, leading to a smaller Insolation value 

  • The area of the Earth that is the most perpendicular to incoming solar radiation will have the highest insolation 

Seasons in the Northern Hemisphere

  • December 21-22: Winter Solstice 

    • Shortest day of the year 

    • Least amount of sunlight

    • Polar night - 24 hours of darkness at the top of the globe

  • March 20-21: Vernal Equinox

    • Day and night are equal in length

  • June 20-22: Summer Solstice 

    • Longest day of the year

    • Over 12 hours of sunlight 

    • Midnight Sun - 24 hours of sunlight at the top of the globe

  • September 22-23: Autumnal Equinox 

    • Day and night roughly equal in length 

Seasons in the Southern Hemisphere

  • When it is winter in the northern hemisphere, it is summer in the southern hemisphere, and vice versa

  • Equinox days are the same

  • Longest day of the year and Midnight Sun is December 20 or 21

  • The shortest day of the year and Polar Night is June 20 or 21

The tilt is Earth’s axis impacts isolation

  • Different parts of earth receive different amounts of Insolation at different times of year because of its tilted axis

  • The general amount of insolation present in the Northern and Southern hemispheres can be predicted because of the regular orbit of the Earth around the sun

  • The Earth has seasons because of its tilted axis 


Unit 4.8: Earth’s Geography and Climate 

  • Large bodies of water stabilize local temperatures 

  • When solar radiation hits land, there is low specific heat and no mobility and quicker temperature increase

    • Specific heat: the amount of energy it takes to raise the temperature by one degree

  • When it hits water, there is high specific heat and high mobility which leads to slower temperature increase

  • Examples of large bodies of water:

    • Great Lakes

    • Gulf of Mexico

    • Mediterranean Sea

Ocean Currents and Land Temperatures

  • Canada and England - virtually at the same latitude, yet Canada is colder than England because of the temperatures of the currents that run alongside of these lands

    • Current from the Arctic Circle makes Canada colder too

Influences on Local Climate

  • Large bodies of water, both fresh and marine, stabilize the temperatures of the land adjacent to the water. They also contribute to the overall moisture content of the air above the land adjacent to the water

  • Currents in large bodies of water can make the land adjacent to the water cooler or warmer than expected

Rainshadow Effect 

  • Part of a mountain with a land and water in front is the windward side, and the other side is the leeward side

  • When ocean breezes hit the mountain, it rises and the air cools. When water vapor cools, it turns into clouds, which leads to rain.

    • Then, this rain will lead to lots of vegetation on the windward side of the mountain

    • The leeward side will be more desert like because hot air travels down this side of the mountain from the clouds 

  • The rainshadow effect predicts the location of rainfall, vegetation, and arid/dry areas along the slopes of coastal mountains and on the leeward side of coastal mountains 

  • The rainshadow effect explains the presence and location of deserts in unexpected locations

    • Convection cells predict that deserts form at 30 degrees above and below the equator, along the Tropic of Cancer and Tropic of Capricorn latitudes


Unit 4.9: El Niño and La Niña

  • ENSO (El Nino Southern Oscillation) - a regular event that occurs every 3-7 years, beginning in December.

    • The location of ENSO event is the Pacific Ocean, below the equator, between Australia and South America

  • Changes in atmospheric winds and ocean currents play a part in ENSO, and affect associated terrestrial areas

Neutral/Normal VS El Niño 

  • Normal wind patterns blow from east (South America) to west (Australia)

    • Easterly trade wind

    • Warm surface ocean currents moving east to west 

    • Upwelling that supports schools of fish along the coast of South America 

  • During El Niño, winds stall

    • May reverse to become westerlies 

    • Note change of location of clouds 

    • Current reverses 

    • Warm surface water driven to coast of South America, suppressing upwelling, moving west to east

    • Fish no longer supported by the food chain associated with the nutrient-rich upwelling

  • What about La Niña? It’s an enhanced neutral condition

    • Stronger trade winds, more moisture driven into atmosphere 

    • Same conditions as neutral/normal, but more intense

    • Note the movement of the warm current closer to the Australian shoreline

    • Enchanted upwelling

    • Increase in evaporation and storm potential

El Niño Weather Patterns

  • Drier conditions in Australia - enhanced risk of drought and fire

  • Warmer and wetter conditions in South America - enhanced risk of floods and landslides

  • Warmer winter in Canada and northern US

  • Places that are typically dry may be more wet

  • Wet places may be drier 

  • Can potentially b damaging to certain habitats

La Niña Weather Patterns

  • Wet places get wetter, dry places get drier, warm places get warmer, cold places get colder

  • Wetter conditions in Australia and Indonesia - enhanced risk of floods and landslides

  • Cooler and drier conditions in South America 

  • Colder winter in Canada and northern US

These weather patterns can have a larger impact on residential areas, agriculture, etc