This area is made up of sedimentary rocks of the Hawkesbury Group. Sedimentary rocks are deposited horizontally.
In some areas the rock layers are not horizontal but tilted at an angle. This has occurred because the tectonic plate forces have caused the rock layers to be tilted.
A number of landslides have occurred in the past due to the weakness of the sandstone which has been eroded by weather.
Glenbrook has a creek which is located at the bottom of the valley and a valley which is called Glenbrook Gorge. Cliffs on the walls of the valley is composed of Hawkesbury Sandstone and has a number of cracks. The texture of the rock has sandy grains and a redish brown colour. Vegetation is thin on the sloping sides of the valley because there is no nutrients for them to grow and no soil. The roots of the plants have no grip to hold onto.
The valley has been formed because of the following process;
Cracks have developed in the sandstone of the valley walls
Erosion has caused the layer of harder rock to be undercut
Running water has eroded the bottom and sides of the valley
Gravity and lack of support due to undercutting, weathering and erosion have caused the boulders to fall into the creek.
The fallen boulders accumulate on the valley floor
When the creek floods, the fallen boulders are rolled along by the running water.
BLUE MOUNTAINS PLATEAU
The plateau reaches a maximum height of over 1000 metres. The two basalt-capped mountains - Mt Wilson and Mt Tomah.
Basalt is an igneous rock which got to the top of the other rock layers of the Blue Mountains Plateau by magna which cut through the horizontal rock layers. It was a vertical intrusion the lava flowed on top of the sedimentary rocks that were originally there. Mt Tomah is not a fold mountain but a volcanic mountain formed by hardened lava.
EN ROUTE TO KATOOMBA VIA CLIFF DRIVE
Steep canyons have been cut away by rivers and gravity. This is formed when the softer rock underlines the harder rock and as a result of weathering the rock is undercut. The softer rock wears away, leaving overhanging rock ledges. The overhanging rock breaks along joints and forms boulders. These boulders collect in talus slops down the base of the cliff. The stream at the bottom gradually carries away the loose rock fragments.
The cliff faces at the top are straight and vertical. This has occurred because the boulders have broken away.
JUST EAST OF LAPSTONE MONOCLINE
The monocline took place slowly which so the Nepean river was able to cut down into the rock layers at a rate that allowed it to retain its course (which at present cuts into the monocline). It is a narrow V- shaped valley cut by the Nepean River.
Echo point overlooks the Jamieson Valley. Consisting of cliffs of Triassic sandstone and shale overlying older rocks. The Narrabeen group rock are located at the bottom beneath the Hawsbury group rock. The 3 sisters is located in Echo Point just to the left which consists of 3 thick columns of rock standing side by side. There are vertical and horizontal cracks in the rocks. Some of the cracks have become much wider than others. This has been cause by ice, water, wind erosion and weathering.
The formation of the 3 sisters started as a flat plateau. This plateau is made of sedimentary rock (ie sandstone). Joints or cracks appears in the plateau. Joints or cracks started to break off the larger plateau. The agents such as erosion continued to wear away the rock. Eventually the sisters formed. There are now 3 sisters standing. Evidence shows that there were 5 sisters because of the 2 smaller rocks next to them.
BLUE MOUNTAINS - a great ecotourism destination.
Blue Mountains is a well known mountain region located in NSW Australia. It is a great Ecotourism because it has natural beauty, culture, history, beautiful scenery, waterfalls, jungles scenery