Surface Processes Weathering and Soils (Let’s Break it Down) (Let’s get ready to crumble!)

Weathering: The breakdown of rocks into smaller particles by natural processes Two types of weathering: Physical(mechanical) Chemical

Frost Action

Talus Slope

Kristínartindar, Skaftafellsjökull Talus Slope in Iceland

Potholes

Plant Action

Animal Action-burrowing moles

Plant and Animal Action

Exfoliation

Exfoliation Half Dome, Yosemite Park, California That’s a ladder with people on it

The view from part of the way up the ladder

Going up?

View from the top of Half Dome

Those cracks are caused by pressure unloading and if they break off it is called exfoliation

Physical weathering Temperature changes can also cause exfoliation

Physical weathering Pressure Unloading makes basalt break into pencil shapes Devil’s Postpile, California

Svartifoss, Skaftafellsjökull

- makes caves

Weathering Weathering is the breakdown of rocks into smaller particles by natural processes. Physical (mechanical) Weathering - breaks down rocks without changing the chemical composition. Chemical Weathering - breaks down rock by changing the chemical composition of the rock

Physical Weathering FROST ACTION – water expands as it freezes, expanding cracks in rocks Works best in moist, variable climates Causes “talus slopes” at base of cliffs Causes potholes

Physical Weathering Abrasion – rocks rub against each other and get scratched Often happens in streams Particles become rounded

Chemical weathering Breaks down rock by changing the chemical (mineral) composition of the rock

Chemical weathering Oxidation – reaction of rocks with oxygen (rust) Not a rock

Rocks that are red on the outside have oxidized

Chemical weathering Hydration, hydrolysis and solution – reactions of rocks with water White tank campground, Joshua Tree National Park

Turns granite into weird shapes Feldspar turns to kaolinite (clay) which loosens the other minerals so they fall off. Turns granite into weird shapes Skull rock, Joshua Tree National Park

Chemical weathering Carbonation – carbon dioxide combines with another substance Can dissolve rocks containing calcite, creating pits and caves

Chemical weathering Organic acids – some plants secrete acids which can weather away rocks Lichen on rock

Chemical weathering Human Activity – sulfur dioxide from exhaust fumes causes acid rain which can cause chemical weathering Cleopatra’s Needle, before and after being moved to NYC from Egypt

Factors affecting weathering Climate (VERY IMPORTANT!) Warm climates favor chemical weathering Cold climates favor physical weathering (frost action) The more moisture, the more weathering Temperate (medium) climates have aspects of both warm and cold climates

Factors affecting weathering This chart is in your review book on pg 132 Describe the climatic conditions which would cause strong chemical weathering.

Factors affecting weathering Weathering or frost action are not taking place at location X. Explain why they do not occur under these conditions

Factors affecting weathering Assume that the rate of precipitation is constant at 150 mm. During what season will the weathering rate be the greatest?

Factors affecting weathering Particle Size and Surface Area The smaller the particles of a rock, the faster they will weather Many smaller particles have more surface area than fewer larger particles

Factors affecting weathering Exposure – if a rock is not exposed to the surface it is less likely to weather Mineral Composition – softer minerals tend to abrade quickly, some minerals will react with acids, water or oxygen Time – the longer a rock is exposed at the surface, the more it will weather

HooDoo

HooDoo

HooDoo HooDoo

HooDoo

HooDoo

How do you Hoodoo?

Products of weathering Sediments – clay, silt, sand, pebbles, cobbles, boulders Soil – an accumulation of weathered material, decaying organic material (called humus), water, air and bacteria Soils develop best when there is weathering of the rock, without erosion.

Soils Parent material – the rock material that is forming the soil Residual soil – soil that is forming directly over the parent material Transported soil – soil forming from transported material (Long Island soils)

Soils Soil horizons – layers of soil possessing different characteristics Soil profile – a cross section of the soil at a particular location Soils tend to be rich in organic material at the top, and composed mainly of weathered rock near the bedrock

Soil Profile

Soil Profile