Earth Cache
You will be walking along The Box Vale Tramway. It was built in 1888 to carry coal mined in the Nattai Gorge to the main southern line at Mittagong. The line passes through several cuttings, a tunnel, and it ends at the "incline" by which coal was brought up from the gorge. The Colliery was closed in 1896 and the tramway was abandoned until 1996 when it was opened as a four-and-a-half kilometer bush walking track. Additional information and maps are available from the Visitors Information Centre in Mittagong. Mobile phone reception should be available on this part of the trail.
Wind Erosion
Aeolian processes - the name is derived from the Greek god Aeolus, the keeper of the winds - pertain to wind activity in the study of geology and specifically to the wind's ability to effect the surface of the Earth.
Winds may erode, transport, and deposit materials and are effective agents in areas with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind, aeolian processes are significant in arid environments and where soft rocks are found.
When rocks are exposed to the hydrosphere (water) and atmosphere (air), the weathering process begins as this changes both the physical and chemical characteristics of the rocks. When rocks start to weather they are ready to be eroded and over time abrasion of the surface by the wind - as well as any air-borne particles the wind might be carrying - slowly etches away the softer weathered material. Sandstone is particularly prone to wind erosion.
The posted coordinates will take you to The Cutting - about a third of the way along the Box Vale Walking Track. In this cutting you will observe evidence of "very recent" wind erosion.
You will also notice that this has been facilitated by an alcove in the side of the cutting that is not typical of this, or other, cuttings. As the wind comes whistling down the main alley-way, so to speak, of the cutting, and it is drawn into this alcove, a swirling effect is created that accelerates the wind at this point and is the main source of the weathering of the rock you see here.
Since we know that the Tramway was built in 1888 we can measure precisely how long it has taken to erode this part of the cutting. That is, 2017-1888=129. So, at the time of making this cache, we know that it has taken 129 years to wear away this much of the rock.
To claim this cache:
1. Briefly describe the rock that has been eroded. Also, briefly describe the surrounding rock that has not eroded. Why do you think the one has eroded and the other has not?
2. Measure the overall height and width of the eroded area.
Optional
3. At the current rate of erosion, how long do you think it will take to wear away a cave large enough to shelter your car (or your neighbor's car if you don't own one yourself)?
Please send your answers to me via the geocaching website - e-mail or message. The answers to these questions should not be included in your log, nor should your log include spoiler photos. You do not need to wait for a reply from me to log your find.
Beware of falling rocks, trees, and branches. Please be careful.