Organ Pipes National Park

The Organ Pipes National Park, abbreviated as OPNP, is a national park located in the Central region of Victoria, Australia. The 121ha protected area was established with the focus on conservation of the native flora and fauna, and preservation of the geological features in the Jacksons Creek, a part of the valley, north-west of Melbourne. It is situated in a deep gorge in the grassy, basalt Keilor plains.Within Organ Pipes National Park, the valley walls of Jacksons Creek expose Pleistocene volcanic rocks of the New Volcanic Group. These 2.5 to 2.8 million year-old basalt lavas, commonly known as "trap rock," fractured during cooling into vertically standing, hexagonal basalt columns. These columns are locally known as the "organ pipes" for which this park is named. Over the last one to two million years, the slow cutting by Jackson Creek of its valley down into the basaltic plains and through the underlying trap rock exposed these geological structures. The bottom of the valley of Jackson Creek also exposes a prehistoric buried creek valley, which is cut into 400 million year-old (Silurian) mudstones and sandstones. The bottom of this buried valley contains ancient creek gravel. Both the ancient river valley and the Silurian sedimentary rock lies buried beneath the basaltic volcanic rocks of the New Volcanic Group. Marine fossils that are found in the Silurian sedimentary rocks demonstrate that they accumulated beneath a prehistoric ocean.