Sandstone and quartzite rocks break, erode and weather in characteristic and often spectactular ways, creating amazing features like Tolmer Falls and the Gorge below.
Sandstone and quartzite tend to fracture in flat planes that are at right angles to each other resulting in block-like eroded structures and sheer cliff walls.
The movement of water along major joint lines accelerates downward erosion and creates deep straight chasms.
Corners and edges of sandstone blocks weather faster than the faces giving the blocks a rounded look.
Building an Arch
Arches form across joint lines in sandstone when the water flowing along the joint line encounters a particulary resistant block of rock.
Unable to erode a course through the resistant block, the water finds an easier path in the rock below.
The ravine widens and deepens straddled by the resistant sandstone bridge above. The original joint line still exists as a hair-line crack through the arch. Over time, weathering smoothes the surface of the arch and conceals the crack.
Tolmer Falls provides examples of these geological processes.
Questions:
Please email me the answers and do not put them in your log entry.
Q1. There are distictive colours in the rock walls. What are the 2 colours and of what minerals?
Q2. Tolmer Creek flows in what sort of lines and what sort of bends.
Q3. Why does Tolmer Creek flow it the way it does i.e. what does it follow?