Blue Mountains

PROJECT

www.j aconline.com.au Blue Mountains

The Blue Mountains — lying west of Sydney — extend from Lake Burragorang in the south to the Colo and Wolgan rivers in the north. They form a part of the Great Dividing Range. The extensive plateau of these mountains has been dissected into valleys and gorges that are flanked by steep cliffs. The mountain range has a maximum height of 1100 metres in the west and slopes gently towards the east. The mountains get their name from the blue haze that surrounds them, thought to be created by sunlight shining through vapour released by eucalypts. The Blue Mountains are a striking example of both the constructive and destructive forces of nature. The diagram on the next page depicts key steps in their formation. Viewfinder Australia Photo Library Photo Australia Viewfinder

1. In groups, construct labelled models (e.g. of  plasticine or clay) that show the stages in the The Three Sisters are a distinctive feature formation of the Blue Mountains, using the in the Blue Mountains. following time periods as a guide — 500 million years ago, 300 million years ago, 170 million years ago, the present day. Each group should present and explain its finished models to the class. (Refer to the sources listed in the References for more information.) 2. As a class, brainstorm the various ways in which people might use the Blue Mountains today. • Choose one of these uses for individual research. Find out how this particular use impacts on the natural environment of the Blue Mountains. • Suggest some strategies that have been or could be employed to minimise this human impact. • Create a series of flow diagrams, based on your findings, which can be displayed in your classroom.

The forces of nature have created some breathtaking landscapes in the Blue Mountains.

 Viewfinder Australia Photo Library

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Some 500 million years ago Bedrock formed through a process called metamorphosis. Sandstone rich in silica and quartz was subjected to great heat and pressure to form quartzite (a very hard, coarse-grained rock, which basically consists of sand grains that have been cemented together).

Some 300 million years ago The region was heavily faulted and folded. Rivers drained into the depression that formed, creating a shallow inland sea. Rivers continued to deposit sediment in this sea — with layers of siltstone, mudstone and shale slowly building up. (This build-up continues today.) Around the sea’s edges, vegetation flourished in the swamp-like conditions. As it died, it was buried under massive amounts of sediment and compressed, forming coal. As this deposition process continued, the huge weight of constantly accumulating sediment (e.g. sand) caused the lower layers of the depression to sink, forming a huge basin. Heat and pressure turned the lower layers into hard rock (sandstone).

Some 170 million years ago Forces deep within the Earth began forcing the landscape upwards. The bedrock bent and buckled and the sandstone that had formed above it fractured. A broad plateau — heavily fractured and jointed — was formed.

Some 150 million years ago Volcanoes sprang to life, spewing lava across the plains. Then, once again, rivers set to work, exploiting any weaknesses in the rocky plateau. They began to carve out the valleys and gorges for which the region is today famous. The rate of erosion is not constant — it has varied according to the composition of the different layers on which the mountains stand.

Stages in the formation of the Blue Mountains

References: SOSE Alive 3, pp. 132–3 ▪ SOSE Alive Geography 2, pp. 36–7 ▪ www.jaconline.com.au/sosealive/sosealive3 (or www.jaconline.com.au/sosealive/sageography2) and click on the Blue Mountains links for this chapter