🌋 APES Geosphere Unit Study Guide (4.1, 4.2, 4.3, 4.6)

4.1 — Plate Tectonics

Boundaries: 

  • Convergent Boundary: Two plates moving torwards eachother

    • Subduction: Denser plate moves under the less-dense plate

    • Can result in mountains, island arcs, earthquakes, and volcanoes

  • Divergent Boundary: Two plates moving away from each other

    • Seafloor Spreading: Magma fills space between plates forming rock

    • Can result in seafloor spreading, rift valleys, volcanoes, and earthquakes

  • Transform Boundary: Two plates sliding past each other in opposite directions

    • Can result in earthquakes

Plate Tectonics Map:

  • Using maps lets us better understand plate tectonics

  • We can use maps to find locations of volcanoes, island arcs, earthquakes, hot spots, and faults

Earthquakes:

  • Occur when stress overcomes a locked vault, releasing stored energy

4.2 — Soil Formation & Erosion

Soil formation starts with parent material, and is broken down through weathering. Other particles can also be introduced through deposition. With presence of vegetation and organisms, soil horizons begin to form and nutrients are added to the soil

Soil Horizons

O

Organic Layer (Humus)

Surface litter (ex. leaves, decaying matter)

A

Topsoil

Mixture of organic materials with minerals

E

Eluviated

Zone of Leaching, nutrients from upper horizons move to lower horizons

B

Subsoil

Zone of Accumulation, minerals like iron accumulate

C

Parent Rock

Partly weathered rock, original material that is broken down to create soil

R

Bedrock

Unweathered rock base

Erosion

  • Soil is very easily washed away by wind and water without vegetation to hold it in place

  • Erosion negatively impacts water quality

  • Vegetation with soil can help filter water, but without vegetation this does not happen

4.3 — Soil Composition & Properties

Water Holding Capacity

The maximum amount of water soil can hold under gravity

  • Retention contributes to land producivity and soil fertility

  • In farming, soil is more desirable when it can hold water in its pores instead of letting it penetrate further into the crust.

  • Increased by:

    • Smaller particles

    • Organic matter

  • Loam is the soil type with the highest water retention with an equal amount of small, medium, and large particles

Properties of Soil

  • Chemical: 

    • pH: How acidic or basic a soil is

      • Impacts what plants can grow

      • Can shift easily, acidic soil often made by pollution or acid rain

    • Cation Exchange: When soil particles attract cations (positively charged ions)

      • Regulates pH

      • High cation exchange capacity increases ability to maintain pH and nutrients levels

  • Physical

    • Aeration: Ability to take in essentials such as nutrients, water, and oxygen

      • Good aeration is crucial to support plant life

    • Soil Compaction: How compacted soil particles are

      • High compaction can negatively affect porosity, permeability, and aeration

      • Heavily compacted soil means there is less space for water, air, or other essential nutrients

  • Biological

    • Are determined by the organisms and plants that live in it, meaning soil composition and consistency varies based on biome and climate. Species like fungi and bacteria can help develop soil composition in ways other species cannot.

Soil Texture Triangle

Soil Texture Triangle (Soil Composition)

  • Allows us to identify soil using percentage of clay, silt, and and sand.

  • The angle of the numbers shows the way the lines run

    • For example, clay lines run straight across because the clay numbers are written normally

    • Sand lines run diagonally, down left-to-right, because that’s the way the numbers are oriented

  • It is used by following the lines to find where they all intersect

    • For example, 20% clay, 50% sand, and 30% silt would be loam

4.6 — Watersheds

A channel (stream, river) that concentrates runoff (water) to the main discharge point (a large body of water). The discharge point is usually the lowest point in the watershed.

They are usually seperated by ridges or mountains that form the highest part of the watershed.

  • Headwaters: Beginning of a watershed

  • Sub-watersheds: Mini watersheds within a larger watershed, but all runoff will eventually discharge into one point

Characteristics:

  • Size (area) can be a reflection of the amount of runoff and what is created by the runoff (stream, creek, etc.)

  • Steeper slopes allow water to flow easier

  • Longer watersheds make water take longer to discharge

  • The type of soil and vegetation impact the amount of runoff water and can also filter the runoff.