The Process of Weathering

Homework: In review book, read chapter 4, pages 95-101; do questions 1-9 on pages 97-98 and questions18-22 on page 100. Go to www.johnbowne.org for more details on homework and study attachments.

What is Weathering? The breakdown of rock due to physical and

chemical changes is called weathering.

Why Do Rocks Weather? When rocks that form within Earth’s crust

are uplifted and exposed to surface processes such as wind, water, and biological activities, rocks become unstable and change in observable properties and mineral composition.

What is Physical Weathering?

The disintegration and decomposition of rock at or near the surface of the earth.  It affects the rocks in place and no transport is involved.  This distinguishes weathering from erosion.

Physical (mechanical) weathering changes the size and/or shape of the rock. It does not change the rock’s chemical composition.

Physical Weathering

Types of Physical Weathering

Frost Wedging: an important agent of physical weathering in climates that undergo seasonal temperature changes alternately above and below 0°C.

Abrasion: The collision and grinding between rock particles as they are transported by wind, water and/or ice.

Types of Physical Weathering

Biological Activity: – Plant roots that grow in the cracks of

rocks expand and gradually push the rock apart.

– Animals that burrow beneath the ground constantly expose new rock surfaces to weathering.

Frost Action

Water seeps into cracks in rocks. The volume of water increase as it freezes. The increase in volume produces a force that makes cracks in the rock larger each time the water freezes.

Abrasion

The photo shows pits that have been eroded into the rock by sandblasting (abrasion). 

Abrasión

La foto muestra hoyos que han sido erosionados en la piedra pulida por chorros de arena (abrasión).

Abrasion

The powerful effect of wind generated abrasion is the Double Arch from Arches National Park.  The edges of the arches have weathered along joints, preexisting tectonically controlled vertical surfaces in the rock. 

Biological Activity

What is the most important kind of physical weathering in high latitude regions?

1. Abrasion by wind2. Oxidation and rusting3. Frost wedging4. Dissolving into solution