GEOG 1113: Landform Geography

Lecture 1:

Soils

Earth’s Internal Structure

Global Distribution & Character of Soils

• What is soil?

• Basic soil characteristics

• Soil-forming processes and factors

• Soil profiles (reading the soil)

• Soil science & classification

• Earth’s internal structure

What is Soil?• Uppermost layer of Earth’s surface with mineral

& organic matter able to support plants

• Transition between atmosphere & rocky Earth

• Provides plants with physical support, nutrients & water

• Plants support soils by anchoring them to Earth

Basic Soil Properties

– Inorganic Material – minerals - natural elements or compounds w/crystalline structure – silicon, aluminum, iron, potassium, calcium, etc. common in soil minerals

– Organic Matter – bacteria & fungi break down remains of plants & animals to form humus – helps soil hold water and increases fertility

Basic Soil Properties• Water – from rain & snow

– Losses to evapotranspiration

– Drainage through soil, leaving air pockets

– Capillary Action – attraction to soil particles

– Surface tension holds some water in soil

– Field capacity – max. water capacity of soil

– Soil-Water Budget – balance of soil-water gains & losses

Soil-Water Budget

Basic Soil Properties

• Air – most air in soil is carbon dioxide

– Plants give off CO2 during respiration & take it in during photosynthesis

– Less air in wet soil because of water

Soil-Forming Processes

• Soils form & evolve through sequence of interrelated pedogenic (soil-forming) processes:

– Soil Additions

– Translocations

– Soil Depletions

– Transformations

Soil-Forming Processes

Soil-Forming Processes

Soil-Forming Factors

• Factors that consistently affect how soils form

– Parent Material

– Climate

– Organisms

– Relief

– Time

Parent Material

• Sediment in which soil forms – related to geology of the region

• Residual Parent Material – sediment from rock that weathers in place

• Regolith – small fragments of weathered rock

• Transported Parent Material – carried by wind, water, or glaciers from where it weathered

Regolith & Soil

Climate

• Temp & moisture influence the kind & rate of biological and chemical reactions in soil

• More reactions in warm, wet conditions, so thicker, more developed soils

• Wetter soils have more eluviation & deeper illuviation b/c of water percolating downward

African Climate, Vegetation & Soils

Organisms

• Plants & animals that reside in soil

• They acquire food from soil & regulate its environment

• Bioturbation – mixing of soil by plant roots and burrowing animals

• Earthworms important as soil recyclers

• Micro-organisms decompose organic matter to humus

Relief

• Differences between highs and lows of landscape – Mts are high relief, plains low relief

• Soils thin & poorly developed on steep slopes

• Sediment eroded more on steep slopes

• Sediment deposited more on areas of low relief where soils deeper & more developed

Elluviation and Illuviation

Bioturbation

Prairie Dog

Ant Hills, Australia

Relief and Soil

Time

• Longer time on a stable surface allows for greater soil development

• Soil in a 10,000-yr-old floodplain more developed than soil on 2000-yr-old sand dune

Measurable Soil Characteristics

• Physical Properties to Distinguish Soil Types:

– Color

– Texture

– Structure

– Soil Chemistry

– Soil pH

Soil Texture Triangle

Soil Texture

Types of Soil Structure

Soil Sampling and Mapping Units

Soil Profiles• Soil processes lead to vertical organization in

soil, layers in a profile visible in cross-section

• Soil Horizon – distinct layer in soil profile

• Horizons blend into each other, no sharp boundaries

• Soil profiles vary in different regions of Earth, depending on soil-forming factors

Soil Science and Classification

• Goal of soil science to understand Earth’s soils in order to preserve & efficiently utilize them

• Classification in US based on soil taxonomy: color, texture, structure & mineral content

• Soil Order – highest level in soil taxonomy

• 12 soil orders occur on Earth

• Soil orders subdivided into many categories

Earth’s Inner Structure

• Major Layers (outside-in):

• Lithosphere

• Upper Mantle

• Lower Mantle

• Outer Core

• Inner Core

Earth’s Interior

Earth’s Interior

Lithosphere

Types of Crust

Asthenosphere

Isostatic Adjustment

Figure 11.4

Earth’s Magnetic Field