Weathering,Soil and Glacial Movement Ch. 14,15

What Physical Properties Affect Rocks Near the Surface? There are many processes that break rocks apart and can change their – color – texture – composition – strength Called chemical and physical weathering

What is the role of joints in weathering Joints are fractures in rock that are not offset. Joints allow water and roots to penetrate the rocks to cause weathering.

Joints Closely spaced joints promote increased weathering. Exfoliation- when overlying rocks are unloaded the underlying rocks expand creating expansion joints.

Physical Weathering Heating and cooling- expansion of rock Frost wedging Mineral wedging- growth of minerals weaken the rock around them

Physical Weathering cont Burrowing organisms Plant growth

Effect of Fracturing on Weathering As a rock fractures and breaks apart there is an increase in the rate of weathering. WHY?? As a rock breaks into smaller pieces the surface area increases allowing more exposure to weathering.

Chemical Weathering Chemical factors that affect rocks at the earth’s surface –Decreased temperature and pressure –Increase O 2 –Increased H 2 O

Dissolving Rocks Rocks are dissolved by weak acids formed in water that react with the minerals that make up rocks. Acids are abundant in H + ions, the H + ions enter minerals releasing other ions Ex- Limestone is rich in calcite which is soluble in weak acids. When Carbonic acid in rainwater reacts with the rock it dissolves.

Oxidizing Rocks Free O 2 is common near the surface and reacts with minerals to cause rust. Most common in iron bearing minerals. Mafic minerals commonly contain iron and are most commonly affected by oxidation.

How Does Water React With Minerals? In some minerals water combines with the mineral causing formation of a new mineral, called hydrolysis. If exposed to wet conditions many rocks convert into clay minerals.

How Does Soil Form Soil consists of weathered rock, plus material from the atmosphere, decaying plants and microbes Soil is made up of different zones, or horizons.

Soil Horizons O Horizon- surface accumulation of organic debris. A Horizon- topsoil, dark gray or brown organic material mixed with minerals. E Horizon- light colored, leached zone B Horizon- little organic material, red color due to accumulation of iron oxide C Horizon- weathered bedrock

Processes That Occur During Soil Formation Soil forms over thousands of years as a result of weathering. Involves the vertical movement of dissolved material up and down through the horizons.

How Materials Move Through Soil Materials move both up and down as carried by water, animals and gravity Zone of leaching- Upper part of soil loses material downward. Water leaches soluble materials and carries them downward. Zone of Accumulation- Chemical ions leached from above accumulate in the lower levels.

Glaciers Moving masses of ice. They form by the accumulation of snow and ice. –Snow falls by individual flakes and then gets compressed until it recrystallizes into solid ice. –Blue color because there is less air.

Glacier Movement Glaciers move downhill because ice is not strong enough to support its own weight. Shearing force – the top of the glacier moves faster than the bottom because of friction.

Glacial movement continued As glaciers move internal stress causes the upper surface of ice to break forming fractures, called crevasses. When the glacier reaches water, it will float. When glaciers break off, in a process called calving, they float off as icebergs.