Biological Weathering and Tree Roots

October 13, 2010


Photographer: Phillip Lachman
Summary Author: Phillip Lachman

There are many ways by which large rocks can be broken down into smaller rocks, but one of the more amazing is through the action of trees and plants. In this photo you can see the force that a tree’s roots can apply. The slab of sandstone has been uplifted and separated from adjacent layers as the root grew in width. The tree, located at Pennant Hills, outside Sydney, Australia, is on Hawkesbury Sandstone and became established on this rocky outcrop probably some 200 years ago. Hawkesbury sandstone is a coarse grained sedimentary rock consisting mainly of quartz particles, with smaller quantities of claystone grains. It weathers to form thin, sandy soils with low water retaining qualities. This soil type is common along ridgelines and native species have evolved to cope with them.

In the upper right background you can see a gum tree with a trunk that forms a horseshoe shape large enough for young children to crawl through. This type of deformation is usually caused by bush fires. One of the interesting features of gum trees is their ability to survive even after major damage to their trunks and canopy. Photo taken on May 22, 2008.

Photo details: Camera Maker: FUJIFILM; Camera Model: FinePix S7000; Focal Length: 7.8mm; Aperture: f/5.6; Exposure Time: 0.0017 s (1/600); ISO equiv: 200; Exposure Bias: none; Metering Mode: Matrix; Exposure: program (Auto); White Balance: Auto; Flash Fired: Yes (Manual); Color Space: sRGB.