Physical Weathering, Soil Formation, and Topography: Key Concepts for Geology

Physical weathering refers to?

breaking down of rock, changes in particle size

Physical weathering does not change?

chemical composition

Coarse grained

Boulders, cobbles and pebbles

Medium Grained

Sand

Fine Grained

Silt and clay (MUD)

Physical weathering

Anything that is taking the rock and slowly breaking it away

Freezing/ Thawing cycles

Ice expands and creates separation in rock, as it thaws it creates a crack, or sometimes separates a large chunk/boulder from a rockface

Roots contribute to weathering of parent material- how?

Roots can also spread rocks creating separations/cracks as they grow

Thermal Expansion

rocks heat up, causing expansion, cold down causing contraction

Exfoliation

outside of rock gets slowly degraded though erosive factors such as wind, rain, Etc.,

How are rocks formed?

Heat and pressure

Rocks are formed where?

below earth's surface, once above the surface they are in a new chemical environment with which they interact and take on chemical changes

Primary minerals

original formation of intrusive rock from below the surface

Secondary minerals

have undergone and least one chemical change

Gravity Fed Deposits found?

at the base of slopes

Gravity fed deposits found at the base of slopes

Colluvium/ colluvial

Deposited by streams

Alluvial/Fluvial

Deposited in Oceans

Marine

Deposited in lakes

Lacustrine

Deposited by ice or water moving off a glacier

Glacial Til/, Moraine

Deposited by wind

Eolian and Loses

Topography

Shape and structure of the environment

The steeper the slope the faster the what?

erosion, and the more water drainage

If the soil remains wet but not soaked, it increases?

fungal and microbial activity

The flatter the slope, the more?

soil development

Aspect

Direction

North facing slopes?

less sun, reduced warmth, and higher moisture , Topography: Shape and structure of the environment

The steeper the slope the faster the?

erosion, and the more water drainage

If the soil remains wet but not soaked, it increases what?

fungal and microbial activity

The flatter the slope, the more?

soil development

Aspect

Direction

North facing slopes get?

less sun resulting in reduced warmth, and higher moisture

South facing slopes

more sun/ increased warmth, lower moisture due to evaporative water loss & less vegetation

The North facing slope will get more what?

soil development due to root systems of plants moving nutrients and dropping organic matter

The North facing slope will get more soil development why?

due to root systems of plants moving nutrients and dropping organic matter

O Layer

Organic layer with decomposed leaves and plants

A layer

topsoil rich in organic matter and nutrients: dark in color

E Layer

eluviation layer where minerals are leeched out, lighter in color (this layer looses its minerals through leeching and it goes into the B horizon)

B Layer

Subsoil with accumulated minerals like iron and clay

C layer

Weathered parent material with minimal biological activity

R layer

Unweather bedrock layer beneath the soil

4 Process of soil formation

Additions, translocations, losses, transformation

Additions

new material (fallen leaves, landslides etc.,)

Translocations

Movement of organic/inorganic material within or between horizons in any direction, includes soil mixing from anima

Losses

Loss of material to groundwater, leeching, erosion or volatilization(gas releases)

Transformation

change from one substance to another (such as primary to secondary materials) includes decomposition of plant matter

Entisol

undeveloped, young soil. Little to not distinct horizons, usually only A horizon.

Alfisol

Moderately weathered, fertile soil