Origin
Dao Vallis begins near a large volcano, called Hadriaca Patera, so it is thought to have received water when hot magma melted huge amounts of ice in the frozen ground. Much of this water may have been released in very large "outburst floods". The partially circular depressions on the left side of the channel in the image below suggests that groundwater sapping also contributed water more gradually.
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Section of Dao Vallis, as seen by THEMIS. Click on image to see relationship of Dao Vallis to other nearby features.
Read more about this topic: Dao Vallis
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“Each structure and institution here was so primitive that you could at once refer it to its source; but our buildings commonly suggest neither their origin nor their purpose.”
—Henry David Thoreau (1817–1862)