Rising 150 metres, the rare rock formation of Mount Scoria is an obvious and impressive landmark. This striking mountain rises above plains of grazing land and features unusual basalt columns, rocky scree slopes, open woodlands, vine thickets and diverse bird life. It has a base less than 2km in circumference.
Between 14.5 and 33 million years ago this was the site of an active but benign volcano. Mt Scoria originated from the mass of cooling lava which remained within the volcano when it became extinct. During the millions of years after the lava solidified, the surrounding soil and softer rock eroded away exposing the mountain as a rugged outcrop of resistant rock.
The making of a mountain:
Mt Scoria is mostly vesicular basalt, a porous rock with tiny holes left from gases trapped in the magma. Its vesicular basalt is shaped into distinct interlocking columns. These were created by a process similar to the formation of cracks in drying mud. When the molten rock first started to cool it developed a solid crust which cracked as it shrank. The cracks began as a surface network then slowly grew deeper as the lava below cooled. In this way long columns or pillars were formed at right angles to the lava surface. They are known as columnar basalt.
Column Formation:
The number of sides on columnar basalt indicates the speed and evenness of cooling. The six-sided columns formed from a slow and regular cooling process while the five, seven and eight-sided columns were formed by irregular shrinkage caused from a quick and uneven cooling process.
Although the mountain's name is derived from scoriaceous basalt, or scoria, this name is slightly misleading. The small amount of scoria here suggests Mount Scoria's volcanic formation was a slow lava flow rather than a fiery explosive eruption.
In the past people have hit the columns forcefully to make different sounds which can lead to significant damage. There is no need to climb the mountain to complete this cache. However, if you do you are discouraged from striking the columns so that these unusual geological formations are preserved for future generations.
You may log this Earthcache straight away but then please email your answers to the questions to the CO. We will contact you ONLY if your answers need extra work. Logs with no answers sent will be deleted. The answers can be found by reading the information boards and a little research. Please do not post your answers in your log.
Q1. What does benign mean?
Q2. What is scoriaceous basalt (scoria)?
Q3. Why is the name Mt Scoria misleading?
Q4. How many sides do most of the columns here have?
Q5. Vesicular basalt is formed by fast cooling or slow cooling lava?
Q6. You are welcome to post a photo of you with Mt Scoria in the background if you wish.