Weathering: the physical and chemical modification of rocks…

Physical Weathering:

Tearing a page of paper to bits…

…does NOT change the composition. It’s still paper!

(Mechanical Weathering)

Chemical Weathering:

Weathering: the physical and chemical of rocks…

A change of composition.

Burning a page of paper…

…changes the composition!

Weathering is the process that breaks up and modifies geologic material.

Physical Weathering

Extremes of heat and cold…

Water and variable freezing temperatures…

Unloading; expansion and cracking of rock after exposure…

…breaks rock into smaller pieces.

Actions of plants and animals…

Chemical Weathering…

…involve processes that change geologic materials CHEMICALLY.

Minerals may be broken up, and components removed…

K

K

K

KK

K K

K K

K

Various chemical processes modify minerals…

Chemical Weathering is controlled primarily by Moisture and Heat…

Heat and Moisture accelerate chemical weathering.

Polar areas have relatively little chemical weathering.

Temperate areas (like Illinois) have considerable chemical weathering.

Tropical areas have EXTENSIVE chemical weathering.

CLIMATE!

Chemical Weathering

Dissolution: Water & Carbon Dioxide

Forms Carbonic Acid…

Which dissolves Carbonates…

CO2 + H2O

= HCO3

…creating limestone caves.

Hydrolysis: how Granite weathers.

Granite is primarily Quartz and K Feldspar.

Hydrogen ions replace the “K” in K Feldspar.

Breaking up the Feldspar & releasing “K” as a nutrient.

K

KK

K

K

Clay and Quartz are the main products of the reaction.

Chemical Weathering

…and there is a LOT of Granite!

Chemical Weathering…

Oxidation

“Rust” is a stable mineral, but not a “strong” material

Iron-rich materials OXIDIZE… They “rust”!

Tropical climates, Mars…

Chemical Weathering is controlled primarily by Moisture and Heat…

…and this means that:

Temperate areas (like Illinois) have considerable chemical weathering.

Tropical areas have EXTENSIVE chemical weathering.

CLIMATE!

Remember!

SOILS

Soils form “in place”...

Soils do NOT “wash in”…

Soils are NOT “deposited”…

Soils are a product of weathering…

How do Soils form?

Physical weathering breaks up minerals into smaller particles…

Chemical weathering breaks up minerals, mobilizing and removing or concentrating components…

Biological processes change compounds, add organic material… K

KK

K

K

K

Soils form IN PLACE!

SOILS

Parent Material

Controls of Soil Formation

Weathering of Basalt would produce different minerals than weathering of Granite!Time

Plants and Animals

And CLIMATE!

We will use a modified Soil Profile…

Organic Layer (Topsoil)

Leached Zone

Accumulation Zone

Parent MaterialPartially altered Parent Material

In Temperate Areas (think “Illinois”)

Plentiful moisture leaches minerals…

While vegetation builds up a substantial organic topsoil

…some of which accumulate in a lower zone.

Pedalfer

In Temperate Areas (think “Illinois”)

Thick organic layer

Well-developed Accumulation Zone

Well-developed Leached Zone

Pedalfer

Generally good “growing soils”

Prairie soils are generally the best

In Desert Areas… (think: “Phoenix”)

Lack of moisture leads to very limited leaching and mineral movement…

Little moisture means little organic topsoil

Most accumulation occurs when moisture, moving UP, evaporates, leaving behind calcium carbonate (CALICHE).

Pedocal

In Desert Areas… (think: “Phoenix”)

Thin Organic Layer

Thin Leached Zone

CALICHE

Pedocal

Little organic material

Poor growing soil without additional nutrients and water.

Caliche layer acts like natural “concrete”

It’s THIN!

In Tropical Areas… (think: “Brazil”)

ABUNDANT moisture leads to EXTENSIVE leaching and mineral movement!

Ironically…abundant moisture means little organic topsoil!

Although tropical areas have an incredible abundance of vegetation, the overwhelming moisture leaches out virtually all minerals, leaving a thin, poor “topsoil”.

Laterite

In Tropical Areas… (think: “Brazil”)

Thin\depleted Organic Layer!

VERY thick Leached Zone

Very THICK soils

LateritePOOR “growing soils”

Laterites “wear out” rapidly

In the Tropics, the removal of trees also removes virtually ALL of the organic material!

And this leads to rapid erosion of the soil, and a devastated landscape.

Laterites are commonly farmed by “Slash & Burn” methods.

Nutrients from burned wood are exhausted in 2-3 years!

Al

C

C

CSi

Si Si

SiK

C

SiK

Mg

K

Si KMg Mg

Al

Al

Al

Al

AlMg

Si

K

K

K

K

Extensive leaching creates a BAUXITE…

The leaching concentrates a fairly high percentage of Aluminum!

Popcans and Airplanes come from this soil…

Aluminum is still relatively expensive…that’s why recycling it is SO important!

The first BIG use of Aluminum?

Aluminum was EXPENSIVE!

Prior to modern technology…

Zeppelins!

Soil Erosion… …is a particular threat!

Sheet Erosion

Rills

Gullies

Soil erosion is greater than soil formation in 1\3 of all the World’s farmland.

Prairie Soils are rich with organic material…

Forest Soils have less organic material…

Bedrock

Glacial Deposits

Over much of the Midwest…

…Glaciers left a thick deposit of clay, sand, and silt.

Loess

…and windblown silt was often deposited as Loess.

Bedrock

In these deposits…

…both prairie and forest soils developed

Loess

Glacial Deposits

Prairies developed in Uplands…

And Wetlands…

And Flatlands…

As did Forests…

…which in certain areas grow in thin soil on Bedrock.

And in some area, soils developed in sand…

And sandy uplands!

So… Without going into TOO much detail…

…There are Forest and Prairie Soils developed in dry, wet, flat, and sandy areas…

…and on Bedrock.

Hickory…Upland Forest

Wellston… Forested Bedrock (South)

Sawmill… Wetland Forest (“Bottomland”)

Forest Soils:

Bloomfield… Sandy Soil

Catlin… Upland Prairie

Drummer… Flatland Prairie (poorly drained)

Cisne… Wet flatland (upland) Prairie

Ipava… Flatland Prairie

Prairie Soils:

Bloomfield… Sandy Soil

Catlin… Upland Prairie

Hickory…Upland Forest

Wellston… Forested Bedrock (South)

Sawmill… Wetland Forest (“Bottomland”)

Drummer… Flatland Prairie (poorly drained)

Cisne… Wet flatland (upland) Prairie

Ipava… Flatland Prairie