The basalt cliffs contain evidence of a number of separate lava flows that filled the valley, most likely from the nearby Mt Franklin volcano. Directly in front of the posted co-ordinates you can see a number of hexagonal columns that developed during the cooling of a thick lava flow because of fractures in the molten rock. If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it can't easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. The topology of the lateral shapes of these columns can broadly be classed as a random cellular network. These structures are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed. The size of the columns depends loosely on the rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns.
If you happen to visit this cache at a time there is no water flowing there is a great example of a tessellated pavement at the foot of where the falls should be.
In order to log this Earthcache you need to email me with your answers to the following questions, looking directly across the riverbed in front of you;
Q1. Looking at the size of the columns do you think they were formed due to rapid or slow cooling?
Q2. What form does the basalt take? Are the columns clearly straight and smooth or are they fractured? Why do you think they are in this form?
Q3. Were the basalt columns formed underwater or in the open air? What brings you to this conclusion?