Australia: The Land Where Time Began

A biography of the Australian continent 

Organ Pipes National Park

This park is close to the Calder Highway, 20 km northwest of Melbourne. There are walking tracks, picnic tables, and water and toilets are available.

Among the native animals here quolls, dingos,

Geology

The Organ Pipes are 20 m high hexagonal basaltic columns up to 1 m in diameter. Some of the smaller pipes are tilted, some almost to the horizontal.

Downstream from the Organ Pipes are sedimentary rocks laid down in a marine environment. The light coloured rocks were formed by the deposition of rock fragments, clay, sand and mud. Included in these rocks are marine organisms such as snails, worms and graptolites, the fossils allowing the rocks to be dated to about 400 million years ago. Over time the rocks in the area underwent upheaval and subsidence, and at presetn are about 80 m above sea level.

The pipes are formed of dark basaltic lava that is pitted with holes that were formed by trapped steam, the bubbles being frozen into rock as the lava cooled. Most of the other rocks of the park are dark grey or brown.

The lava that formed the pipes, is thought to have come from low volcanic hills about 6 km north of the park about 1 million years ago. These volcanoes are believed to be extinct, though they may be only dormant. Western Victoria, where he Organ Pipes are situated, was covered by many thin layers of lava flow from many different volcanoes, together forming the 3rd larges lava plain in the world, stretching from Mt Macedon to Laverton and Williamstown. Half way down from the car park of the Organ Pipes the quartz and quartzite gravel is part of a deep stream bed, a lead, that was buried by a lava flow. It was subsequently uncovered by erosion as Jackson Creek cut down through the lava. It was these deep leads that were mined at Ballarat during the Gold Rushes.

The car park of the park is on the remnants of a very weathered scoria cone that was producing its scoria at about the same time as the larger volcanoes to the north were erupting. It produced the scoria in a series of explosive eruptions. The scoria is brownish and filled with air pockets.

A large outcrop of basalt, Rosette Rock, in which the columns are in a radial array, having formed by radial cooling in what was probably a spherical chamber formed by an earlier lava flow.

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading