Ancient Lava Flows of the Ebor Volcano EarthCache
Ancient Lava Flows of the Ebor Volcano
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The Ebor Volcano was one of a number of central volcanoes formed during the period of extensive Tertiary intraplate volcanism in eastern Australia. The volcano was centred south-west of Dorrigo close to the northern edge of the Bellinger River valley. Geochronological studies designate a Miocene age for the volcano between 19 and 20 million years ago. Reconstruction conservatively indicates that it was a low shield form volcano that was 45 km across and 800 m high. It was constructed on Late Palaeozoic to Early Mesozoic rocks of the New England Orogen. Erosion has removed 90% of its volume and accounts for the red, fertile soil of the district.
The Ebor Volcano last erupted 19.6 to 19.2 million years ago. If you stand at GZ and look across to Dangar Falls the surrounding rock walls, ledges and rocky bed of the Bielsdown River are the result of a succession of lava flows from the ancient Ebor volcano. These flow sequences are up to 400 m thick and cover an area of 480 km2.
The cliff face to the left of the falls reveals a curved and irregular "organ pipe" structure caused by the shrinkage of lava as it cooled. The continued slow movement of the lava during the cooling process has prevented the formation of regular vertical hexagonal columns. These columns are often overlooked as the view is dominated by the waterfall.
To log this EarthCache e-mail the cache owner the answers to the following questions:
(1) The lava flows are made from what type of rock?
(2) What is the name of the process where lava cools and shrinks to form "organ pipe" structures?
(3) When standing at GZ, are most of the exposed ends of the organ pipes facing to the left or the right?
Additional Hints
(Decrypt)
Znxr fher lbh ernq gur arneol vasbezngvba obneq.