Many things cause this to happen. There are two types of weathering:

Mechanical (physical)Chemical

It is when rocks break down into smaller pieces because of some physical force. The rock does not change chemically, it just gets smaller! Sometimes called PHYSICAL weathering.

Photo by A. Criminger

Freezing and thawing is breaking these rocks apart!Ice Wedging

Photo by A. Criminger

Ice is breaking these rocks apart

Photo by A. Criminger

Roots are breaking these rocks apart.

ROOTPRY

Chemical weathering occurs when rocks are broken down by a chemical reaction. This can happen by water, oxygen, acid rain, and even living things.

http://web.mala.bc.ca

http://www.arts.tas.gov.au

http://www.geo.lsa.umich.edu

http://www.raisethehammer.org

On rocks

On man made objects

Photo by A. Criminger

Sometimes rocks are not the only things that get chemically weathered!

Copyright © Bruce Molnia, Terra Photographics

Carbon dioxide combines with water and forms a weak acid. This acid, over time can dissolve rock.

www.nullarbornet.com.au

Photo by A. Criminger

This rock is being broken down by the chemicals in the roots of the lichen growing on the rock.

http://www.geo.lsa.umich.edu

http://www.cartage.org.lb/

1. Type of material being weathered

2. Climate – warm climates weather material faster.