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06 September 2011

The Blue Mountains, Australia

(Click on image for larger view.)

The Blue Mountains rise to a broad plateau not far west of Sydney, Australia. In the heart of the mountains lies the Grose Valley, bounded by sheer 300-meter (1,000-foot) cliffs. This dramatic landscape was sculpted by forces of erosion acting on the underlying geology; that is, characteristics of each rock type helped determine the topography.
This natural-color satellite image was acquired on September 13, 2000, by the Enhanced Thematic Mapper Plus (ETM+) on Landsat 7. Deep green forests, dominated by eucalyptus trees, cover the landscape. The light gray buildings of Blackheath lie just to the west of the valley (lower left), and the light green orchards and pastures surrounding Berambing are visible to the northeast (upper right).
Two main types of rocks make up the Grose Valley and the immediate surroundings: a young, thin layer of volcanic rock, and a thick sequence of sedimentary rocks, laid down by wind and water several hundred million years ago. Several distinct types of shale, sandstone, and siltstone appear in the sedimentary sequence, which comprises the bedrock in most of this image.
The topmost layer is comprised of basalt erupted 15 to 18 million years ago from an unknown source. Most of this basalt has eroded away, but some can still be found at high points like Mount Tomah. Soils in these areas support a unique ecosystem called NASA Earth Observatory image by Jesse Allen and Robert Simmon, with Landsat data from the USGS Global Visualization Viewer. Caption by Robert Simmon.
Landsat 5 - NASA