This is the second of our EarthCaches in the area that show case this amazing landscape. The other is Glass House Lava Plugs.
The published co-ordinates will take you to a picnic area which is a short easy walk from the car park situated at S 26.53.448 E 152.53.118. All questions and tasks can be completed using both co-ordinates.
HISTORY
The Glass House Mountains were named by Lieutenant James Cook in 1770. It is believed that Cook thought the peaks resembled the glass furnaces in his home county of Yorkshire, England.
For generations the Glass House Mountains have held great significance for the Jinibara Aboriginal people. Their creation stories and beliefs are reflected in the strong links that remain today. Because these mountains are of high spiritual significance to the local indigenous people, Mt Beerwah is the most sacred of all the mounts in the area and is considered the "ancestral mother" it is a "women's place" to the Aborigine as it is here that Aboriginal mothers came to give birth. You are asked to be considerate and use only the existing walking tracks and lookouts provided.
GEOLOGY
Intrusion of sub-volcanic rhyolite and trachyte plugs
At about the same time as the eruption of the basalts (25 million years ago) numerous dome-like plugs of rhyolite or trachyte magma were intruded through surrounding older rocks, presumably filling volcanic vents or sub surface bulges (laccoliths). They are now exposed as steep sided peaks as they have resisted erosion while the surrounding softer rocks (predominately Landsborough Sandstone) have been worn away. Judging from the likely height of the land at that time, it seems that at least some of the plugs protruded above the land surface. These vents may have previously been the source of the basalt lavas of Mapleton-Maleny and Buderim.
The plugs, rich in silica, are composed of unusual rhyolites and trachytes that are high in the alkali elements sodium and potassium. They commonly display predominantly yellow, pink, pale grey and other light colours. Silica-rich lavas are thick like porridge and leave characteristic steep sided volcanic plugs.
Many of the plugs have well developed columnar jointing. The face of Mt Beerwah which is visible from the GZ is one of the most prominent examples, Its exposed columns are dubbed ‘The Organ Pipes’. Such long columns suggest the lava was extruded rapidly, generating a large volume that solidified and cracked as one extrusion.
The plug we know as Mt Beerwah, unlike the other 8 mountains, is made up of trachyte. The remainder are rhyolite. Trachyte, or alkali trachyte as it is more correctly known, is a very fine grained rock similar to rhyolite but with less quartz.
Once you complete the EarthCache requirements you can post your find without delay, as per the EarthCache guidelines. You will also need to verify your find by sending us a message with your answers to these questions and we will answer in due course:
Email us the answers to the following questions: Please note; all answers are available on the cache page above, by observation or on the information signs in the parking area. You should leave the GZ with all the required answers.
1. Use the text "Mount Beerwah - GC6MAZP" in your email.
2. Standing at the published co-ords tell us how many faces have the pipe like feature?
3. If the main pipes face (as shown in the picture) is vertical then at what angle to the main face is/are the other/s?
4. What makes Mt Beerwah different from the other "plugs" in the area?
5. The plugs are high in what two mineral elements?
Please DO NOT post answers with your log.
Source: Glass House Mountains Visitor and Interpretive Centre