Some 120 million years ago, several very large volcanoes were formed as the Australian land mass drifted northwards over a stationary 'hot spot' in the mantle deep below the Earth's crust. Two of these were in the Lamington region, erupting about 20 to 23 million years ago. The Focal Peak shield volcano near Mount Barney was the first, but its lavas were later overlapped by flows from a huge volcano centred over present-day Mount Warning. This Tweed shield volcano erupted numerous times, spewing masses of molten lava onto the surrounding landscape from what is now Lismore in the south, to Tamborine in the north.
Most of the eruptive lavas were basalt. There were also some large flows of rhyolite interspersed with multiple layers of ash and boulders which gradually created the massive Tweed shield volcano with a diameter of over 100km.
When the volcanoes finally became dormant, water took over. Over time, spectacular waterfalls, deep gorges, distinctive peaks and rugged cliffs were gouged out of the volcanic rock to create this impressive landscape.
Today, the turmoil of this area's volcanic origins is mostly hidden under the spreading greenery. However, this unique location not only provides spectacular 360 degree views, but also offers one the best vantage points to view one of the world's finest examples of an ongoing geological process, significant to the Earth's history.
To log this Earthcache you need to go to the posted coordinates. After you have enjoyed the magnificent views, take a moment to look around you and examine your surroundings and particularly the exposed cliff lines.
1) Briefly describe the landscape you see before you.
2) What do you notice about the exposed cliffs? what striking feature can you see?
3) What do you think has caused this feature?
You can log this cache immediately but you should email us with your answers soon afterwards to avoid your log being removed.
More information on the Tweed Caldera can be found at: http://www.bigvolcano.com.au/natural/wollum.htm. Reference: "The Mount Warning Shield Volcano. A General Geological and Geomorphological Study of the Dissected Shield" by P. J. Solomon.