Lynch's Crater: A 230,000-Year Window into Australia's Past
Today we visited Lynchs Crater.
At first glance, this unassuming swampy depression might not catch your eye, but beneath its surface lies an extraordinary record of Australia's changing landscapes, climate fluctuations, and human impact stretching back 230,000 years.
Lynch's Crater was born in a violent volcanic eruption, creating what geologists call a "maar" - a broad, low-relief crater formed when hot magma contacts groundwater, causing a steam explosion. Located at 760m above sea level and measuring about 700m wide, this crater initially formed a deep lake with steep sides.
What makes this site so valuable to scientists is the continuous accumulation of sediments since its formation. These layers contain pollen, charcoal, and other materials that reveal the environmental history of northeastern Australia in remarkable detail.
The story revealed by sediment cores is fascinating. For the first 40,000 years of its existence, Lynch's Crater was a deep lake with little marginal vegetation. Over time, the basin gradually filled with sediment, with open water conditions persisting for about 120,000 years.
Around 70,000 years ago, enough sediment had accumulated to allow swamp vegetation to invade much of the lake. By 50,000 years ago, swamp vegetation likely covered the entire basin - a condition that continues to the present day, though with changing plant communities over time.
Perhaps the most striking pattern in the pollen record is the cyclical expansion and contraction of rainforest in response to glacial-interglacial climate cycles. Researchers identified seven major vegetation phases:
- 230,000-190,000 years ago: Complex rainforest dominated during this warm, wet interglacial period
- 190,000-130,000 years ago: Drier conditions led to Araucarian vine forest as the climate cooled
- 130,000-70,000 years ago: The Last Interglacial period saw rainforest reach its peak development
- 70,000-45,000 years ago: Early glacial conditions favoured Araucarian forest and increasing sclerophyll vegetation
- 45,000-15,000 years ago: The Last Glacial period coincided with human arrival and increasing fire
- 15,000-2,500 years ago: Sclerophyll vegetation (eucalypts and casuarinas) dominated the landscape
- 2,500 years ago to present: Rainforest recovered somewhat during the Holocene, with periods of swamp forest
One of the most significant findings from Lynch's Crater is the clear evidence of human impact beginning around 45,000 years ago. The sediment record shows an abrupt increase in charcoal that coincides with a decline in fire-sensitive vegetation, particularly Araucaria (kauri pine).
Before human arrival, fire was not a significant feature of this environment. The research suggests that human-induced burning, combined with drier glacial conditions, transformed the landscape by accelerating the replacement of fire-sensitive rainforest with fire-tolerant eucalypt woodland.
Standing at the edge of Lynch's Crater today, it's remarkable to think about how this landscape has transformed over hundreds of thousands of years. Even more thought-provoking is how human intervention 45,000 years ago continues to shape what we see.
For more information, the Kershaw research paper can be found at:
