Rates of Weathering

1. What is differential weathering? How does surface area affect the rate of weathering? How does climate affect the rate of weathering? Why do mountaintops weather faster than rocks at sea level? Rates of Weathering

2. Differential Weathering • Differential weathering is a process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind. • Hard rocks weather more slowly than softer rocks.

3. The Shape of Rocks • Weathering takes place on the outer surface of rocks. • The more surface area exposed to weathering, the faster the rock will be worn down. • As the surface area increases, the rate of weathering also increases. • If a large rock is broken into smaller pieces, weathering of the rock happens much faster. • The rate of weathering increases because a smaller rock has more surface area to volume than a larger rock. • More of the smaller rock is exposed to the weathering process.

4. Weathering and Climate • The rate of chemical weathering is faster in warm, humid climates than cold, dry climates because of oxidation. • Oxidation happens when the temperature is higher and when water is present. • Water increases the rate of mechanical (physical) weathering (ice wedging). • Repeated changes in temperature (freeze, thaw, freeze, thaw) is a major factor in mechanical weathering.

5. Weathering and Elevation • Mountaintopsweather faster than rocks at sea level because they are exposed to more wind, rain, andice than rocks at sea level or lower elevations. • The increase in wind, rain, and ice increases the effects of mechanical and chemical weathering. This increase in elevation causes peaks of mountains to weather faster. • Gravity affects the rate of weathering: • Steepness • Rainwater • Removal of sediment exposes new rock to weathering • Abrasion • Increased surface area of mountain

6. Summary • Hard rocks weather more slowly than softer rocks. • The more surface area of a rock that is exposed to weathering, the faster the rock will be worn down. • Chemical weathering occurs faster in warm, humid climates. • Weathering occurs faster at high elevations because of an increase in ice, rain, and wind.

7. Quick Check What three factors determine the rate at which rock weathers? 1. 2. 3.

8. Quick Check The process by which softer, less weather resistant rocks wear away and leave harder, more weather-resistant rocks behind is called A. mechanical weathering B. chemical weathering C. differential weathering D. acid precipitation

9. Quick Check Weathering takes place • at different rates • on the outer surface of rocks. • on all rocks equally. • inside the rocks.

10. Quick Check Because of a large rock’s volume, it will • weather unevenly. • weather relatively quickly. • not weather at all. • weather relatively slowly.

11. Quick Check What is the average weather condition in an area over a long period of time called? _______________

12. Quick Check Chemical weathering such as oxidation occurs more quickly in a climate that is ___________ and ________________. 1. 2.

13. Quick Check Weathering occurs faster at high elevations because of • an increase in wind but not ice or rain. • an increase in ice and rain but not wind. • a decrease in wind, ice, and rain. • an increase in wind, ice, and rain.