Warrumbungles - Core Values
The Warrumbungle Range in northern New South Wales, a spur of the Great Dividing Range, is what remains of a period of volcanic activity in the area between about 13 and 17 million years ago. The hills and jagged outcrops of this range differ in appearance from the rounded mountain ranges to the west. The Warrumbungles are low, even by Australian standards, at about 600 m, but there are many isolated spires, domes, bluffs and other shaped peaks that rise to about twice the height of the main range.
Before the period of volcanic activity began the area was a sandstone and shale plateau that had been eroding for some time. The active phase began with a period of seismic activity during which lines of weakness in the floors of the valleys became fault lines. Vast amounts of lava spread from the fissures that formed along these fault lines, so much so that even deep valleys were filled and a thin cap was formed on the peaks, and rivers were dammed or diverted. The accumulating lava eventually formed a huge basalt mound. The character of the lava changed from this point, becoming thicker, and carried volcanic bombs, breccias and tuffs.
The lavas of the final stage of volcanic activity were more viscous, slow-moving trachytes that cooled rapidly, remaining close to the sites of eruption. Their main constituents were quartz and alkali feldspar, eventually congealing sufficiently to plug the vents.
When the volcanic activity ceased the mountains formed by the activity were much higher than they are at present. Weathering and erosion eventually reversed the landscape, the softer sedimentary material of sandstones and shales being removed to such an extent that the more resistant volcanic material, that had filled the valleys and any other hollows, grew in height above the surrounding plain and the surrounding rocks were worn away, leaving the volcanic rocks as mountains. The trachyte pinnacles and domes were the dykes and volcanic plugs that formed before the volcanic activity subsided.
Most of the softer volcanic rocks, as well as those that were shattered by the explosive eruptions, have disintegrated to form rich soils on the plains. Around the valley of Wambelong Creek is a rim in the shape of an amphitheatre. Most of the major peaks of the Warrumbungles are situated along this rim. Mt Wambelong is the highest peak on the rim, standing 1205 m above sea level.
The most spectacular structure is the Breadknife, a narrow trachyte wall that reaches 100 m on the western side and tapers to a crest that is less than 2 m wide at the top. It was formed as a dyke in the same crater that was plugged by what is now the 1094 m high Crater Bluff. Belougery Spire is a 1061 m trachyte tower that originally plugged a subsidiary vent. Grand High Tops is a large ridge. Bluff Mountain is a 1200 m high massive dome. Tonduron Spire, 1130 m high, is a basaltic tower. To the north, Belougery Split Rock at 770 m high, is a white trachyte dome that dominates the lower mountain country.
At the carpark you will find the trailhead, which leads you on an easy 500 metre formed walking track, which is suitable for assisted wheelchair access and takes you to GZ. Whitegum Lookout will give you spectacular overall views of the Warrumbungles and information signage.
Now for the interesting part. To log this cache as a find you will need to send the answers to the following questions.
1) From your observations, describe in your own words the distinctive shape of the Breadknife.
2) Estimate the distance between the Breadknife and Belougery Spire and describe the differences in shape between the two formations.
3) Bluff Mountain was formed late in the volcanic activity period. What shape is it and how do you think it was formed?
4) Please post a photo with your log with these features in the background and include something personal, that identifies you or your team name.