There are 2 primary forces that shape our landscape: 1. Weathering and Erosion (destructive) –wears the land down 2. Mountain Building (constructive) –builds the land up When these 2 opposite forces actively equal one another, the area affected is in dynamic equilibrium

weathering Weathering is the breakdown of rock (the earth’s crust) by either physical or chemical means

Physical Weathering 1) Freeze-Thaw or Frost Wedging 2) Exfoliation 3) Biological or Root Action

Freeze-thaw

Talus slope

Frost heaves form by the same process

Biological weathering What has caused the cracks to appear?

Plant action

The tree roots are breaking up the curb stone

Exfoliation or onion-skin weathering During the day the sun heats up the surface of the rock causing the rock to expand. During the night the rock cools down and contracts. As the rock expands and contracts over and over again, small pieces of surface rock begin to flake and fall off. Onion-skin weathering is a form of physical weathering.

Exfoliation dome

Exfoliation on this boulder Like peeling the layers off an onion

How do you think these rocks have become weathered? Chemical weathering How do you think these rocks have become weathered?

Chemical weathering Plant action

Hieroglyphics almost gone due to humid climate in NYC hieroglyphics as they appeared in Egypt

Chemical weathering occurs fastest in tropical climates (hot and humid) because high temperatures and water both speed up chemical reactions

Frost action occurs best in cold mountain climates

exfoliation works best In highland or dry climates

exfoliation dome in Yosemite National Park

Chemical weathering from salt water in waves pounding this cliff

The final product of weathered rock is sand or soil, depending on available organic material

100 years ago 7 years ago 35 years ago present What happens to the rate at which rock weathers as It breaks into smaller pieces?

Why would a rock weather faster as it breaks into More pieces? Answer: more surface area becomes exposed to atmosphere

very hard rock Soils that develop from the rock directly underneath are called residual soils very hard rock Soft rock Which rock will develop top soil fastest? the average rock takes 100 years to develop 1 inch of top soil

As rock weathers 4 horizons of soil develop “A” horizon topsoil (w/ humus, organics, biological activity) “B” horizon subsoil “C” horizon Partly weathered bedrock “D” horizon Unweathered bedrock

Types of soil Residual soils form in place by weathering Transported soils are brought from other areas, usually by glaciers Most soils in NY are TRANSPORTED