Weathering and Erosion
Definition Weathering and Erosion are the processes that sculpt and mold the surface features of the earth There is a constant conflict between forces that cut down the surface and forces that raise the surface
Weathering The breakdown of material By air, water, plants, and animals
Erosion Movement or transport of that weathered material
2 Types of Weathering Physical Weathering Mechanical breakdown without chemical change Abrasions Ice Wedging Exfoliation
Abrasions Wearing down or smoothing of a material due to constant collisions Beach glass, sand blasting
PHYSICAL WEATHERING ABRASIONROCK PARTICLES GRIND AGAINST ONE ANOTHER
Ice Wedging (Frost Action) Break up due to repeated freezing and thawing Pot holes
The Bigger the crack gets, the more water it lets incausing a snowball effect
Exfoliation Peeling away of surface layers, caused by changes in Temperature and pressure or vegetation (trees, grass, vegetation growing on rocks.) Roots wedge into pores and cracks, splitting the rock
PHYSICAL WEATHERING ROOT ACTIONPLANT ROOTS UPLIFT AND FRACTURE ROCK
PHYSICAL WEATHERING EXFOLIATION
Sand is the remains of weathered and eroded rock!
Chemical Weathering Rock broken down by chemical action, changes the compostion of rock (O2, H2O, CO2)
Oxidation When O2 chemically unites with minerals O2 and Fe (iron) form FeO2 (iron oxide or rust)
Hydration H2O chemically unites with minerals Feldspar and Hornblade plus H2O makes clay.
Carbonation CO2 chemically unites with minerals CO2 + H2O = weak carbonic acid (acid rain) Carbonic acid dissolves limestone creating caves
CARBONATIONStalagmites and stalactites
WHAT KIND OF CLIMATE SUPPORTS WEATHERING?HIGH PPT LOW PPT COLD HOT
How does climate affect weathering? Physical Weathering Works better in a cool and dry climate
Chemical Weathering Works better in a hot and moist environment More water = more weathering
WHICH DIAGRAM IS AN ARID CLIMATE? HUMID CLIMATE?A B
Humid more rounded
Arid more angular
Weathering Rates Note to everyone! Time is a relative thing, when we talk about time in geology, we must remember that the earth has been around four billions of years! 100 years compared to 1,000,000,000 is very small!
Weathering Rates Climate Dictates temperature and amount of moisture #1 factor in weathering process
Weathering Rates Surface area exposure More surface area = greater weathering Which will weather The fastest?
PHYSICAL WEATHERINGINCREASES SURFACE AREA MORE CHEMICAL WEATHERING CAN OCCUR
Surface Area Which will weather faster, solid rock or crushed rock
The crushed rock of course! The large rock is tightly packed and has less surface area exposed The crushed rock is loosely packed and has more exposed.
Mineral Composition The harder the rock, the slower the rate of weathering is Composition dictates hardness which determines resistance to weathering.
WHICH LAYER IS MORE RESISTANT TO WEATHERING? LEAST RESISTANT?
Soil One of the major products of weathering is soil
Residual Soil Forms from the weathering of the underlying bedrock
Transported Soil Different in composition from underlying bedrock. Ex. Long Island soil
It takes hundreds of years for soil to form Average is 2.5cm3 per year
What type of soil do we walk around on? Most soils are transported
TRANSPORTED SOILS DUE TO
Welcome to Huntington Cemetery! Step inside to another real-life weathering laboratory!
Wow! We havent even stepped inside and we have evidence of weathering in the gate!
What process is this and is it physical or chemical?
We are going to look at cemetery rocks (tombstones!) and observe the weathering that has occurred in them.
Since tombstones are dated we can even determine how long the weathering has occurred!
Here is a typical marble tombstone which used to be a very popular rock for cemeteries. What mineral largely composes the rock marble?
What is the hardness of this mineral? Why was it a good rock for tombstones?
Here is another type of tombstone. It is made up of slate.
Compare the two tombstones in the next picture. How do they differ in terms of the types of weathering that has occurred to each? How do they compare in appearance? Which appears more weathered?
Which tombstone is older?
This means that rocks can weather at different rates!
This is called Differential Weathering Rocks weather at different rates due to differences in mineral composition. Some minerals are more stable at the earths surface than others! These take longer to weather.
Calcite is very unstable at the earths surface in certain climate types. Which
CO2 CO 2
What weathering process causes the tombstones to dissolve? Is this chemical or physical?