Mechanical Weathering

Tafoni on sandstone, Salt Point State Park
Michael Szönyi/Imagebroker/Getty Images

Definition:

Mechanical weathering is the set of various processes of weathering that break apart rocks into particles (sediment).

There are five major mechanisms of mechanical weathering:

  1. Abrasion is the grinding action of other rock particles due to gravity or the motion of water, ice or air.
  2. Crystallization of ice (frost shattering) or certain minerals such as salt (as in the formation of tafoni) can exert enough force to fracture rock.
  1. Thermal fracture is the result of rapid temperature change, as by fire, volcanic activity or day-night cycles (as in the formation of grus), all of which rely on the differences in thermal expansion among a mixture of minerals.
  2. Hydration shattering may strongly affect clay minerals, which swell with the addition of water and force openings apart.
  3. Exfoliation or pressure release jointing results from the stress changes as rock is uncovered after its formation in deep settings.
See examples of these in the mechanical weathering picture gallery.

Mechanical weathering is also called disintegration, disaggregation, and physical weathering. Much mechanical weathering overlaps with chemical weathering, and it's not always useful to make a distinction.

Also Known As: Physical weathering, disintegration, disaggregation