Bromfield Swamp EarthCache

The Wet Tropics of Queensland along with the Great Barrier Reef are two exceptional World Heritage listed natural assets adjacent to each other in North Queensland.

Not far from Malanda on Upper Barron Road is the extinct volcanic crater known as Bromfield Swamp. Each winter it becomes a roost to hundreds of sarus cranes each winter.

When we visited there was not a crane in sight but there is a viewing platform from where you can observe.

The geology of the Tablelands Region is one of dramatic change interspersed with long periods of gradual and steady transformation. Around 7 million years ago the story of the Atherton Tablelands was a violent volcano one, vast amounts of lava flowed from a number of shield volcanoes spreading over the landscape and cooling to form a dense layer of basalt.

Later events were more explosive, creating volcanic cones and craters which are a feature of the landscape. It is thought that the most recent eruptions were probably less than 20,000 years ago.

Broomfield Swamp is a maar , formed by the explosive interaction of rising lava with underground water. Periodic stream explosions fragmented the wall rocks and erupted the debris and volcanic ash forming a long ring of volcanic deposits around the vent. A tributary creek of the North Johnstone River has breached the ring on the eastern side.

After the volcanic eruptions ceased, material washed in from the edges and vegetation accumulated forming the peat swamp you see before you. Scientists have recovered cores of the layers of peat down to the underlying sediment. These cores have been used to analyse the types of pollen that fell into the swamp during the past few thousand years.

Similar pollen layers have been analysed and dated in several other craters on the Tablelands e.g the nearby Lakes Eachem and Barrine. All show the Tableland was covered in eucalypt forest before 8,500 years ago suggesting the climate was drier. The older craters reveal a previous cycle in the vegetation with rainforest the dominant vegetation more than 80,000 years ago, then a driers forest from about 38,000 years ago and a return to the present rainforest around 8,500 years ago.

To log this earth cache you will need to answer the following questions.

1. Name and date the three peat units that scientists have identified.
2. Indicate the thickness of the most recent Peat unit.
3. Describe the the pollen found in each unit
4. (optional) a picture of your team with the swamp in the background.

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 me an email providing your answers to the questions.