Welcome to Bowral Lookout
I’m standing on top of Bowral Lookout right now, taking in the sweeping view of the Southern Highlands. Welcome to this breathtaking spot, where the landscape has been shaped by millions of years of volcanic and sedimentary forces. From here, I see the rugged landscape unfold, shaped by millions of years of geological forces. The lookout itself is perched on a solid basalt cap, standing tall and strong against the surrounding softer sandstone. Below me, the sandstone has eroded over time, carving out the valleys and ridges I can see in every direction. The land around me tells the story of weathering and erosion, and as I look out, I’m seeing Earth’s powerful processes at work in real time. It’s incredible to be standing in the middle of this ancient landscape.
The Basalt Cap
Bowral Lookout’s elevation is due to the hard basalt that caps it. Basalt is a volcanic rock formed when lava cools rapidly on Earth’s surface. The basalt here is part of a large volcanic event that occurred around 60 million years ago. The lava flows cooled and hardened into basalt, while the surrounding, softer sandstone was gradually worn away through erosion.
Basalt is far denser and harder than sandstone, making it more resistant to the natural forces of weathering. This is why the lookout remains elevated while the softer sandstone below erodes over time.
Though durable, basalt eventually breaks down into fertile soil, supporting agriculture in the Southern Highlands. The breakdown of basalt contributes valuable minerals to the soil, which helps the local farming community thrive.
The Sandstone Below
The landscape around Bowral Lookout is mainly composed of Hawkesbury Sandstone, which formed around 200 million years ago during the Triassic period. This sandstone is a sedimentary rock formed by the gradual accumulation of sand, which over time became compacted and cemented into solid rock.
Unlike basalt, sandstone is highly susceptible to erosion, which is why valleys and ridges are carved out over time. Sandstone weathers through both physical processes (like freeze-thaw weathering) and chemical weathering from rain.
The basalt cap at Bowral Lookout shields the summit from erosion, preserving its height. However, as the surrounding sandstone erodes, valleys continue to deepen and expand.
Shaping the Landscape
Bowral Lookout offers a clear view of the landscape shaped by geological forces over millions of years. The contrast between the hard basalt and softer sandstone illustrates differential erosion. While basalt resists weathering, sandstone erodes more easily, forming valleys and altering the landscape over time.
Erosion, driven by wind, rain, and temperature changes, continuously reshapes the Southern Highlands. The surrounding hills and valleys tell the story of these long-term processes in action, with the lookout remaining a testament to the power of geology.
Logging Tasks
To complete this EarthCache, answer the following questions:
- Describe the rock at Bowral Lookout, including its colour and texture. Is it basalt or sandstone?
- Looking at the landscape below, how has erosion shaped the valleys? How does the lookout compare in height to the surrounding land?
Logging Instructions
Take a photo with the view of Bowral Lookout in the background if you wish. Please send your answers via email or Geocaching Messenger within 10 to 14 days. Logs may be deleted if answers are not received.
References
- Fossils Australia: Geology of the Illawarra & Southern Highlands
- Geological Society of Australia: Volcanism and Basalts of the Southern Highlands
- Australian National University: Understanding Erosion and Weathering