Mount Kembla: The Extinct Volcano of the Illawarra
Welcome to Mount Kembla, the remnant of an extinct volcano that once shaped the Illawarra landscape. Rising 534 metres above sea level, this peak offers a stunning view of the Illawarra Escarpment and coastal plain. However, beyond its beauty, Mount Kembla tells a fascinating story of volcanic eruptions, geological change, and erosion over millions of years.
Mount Kembla stands as a distinct feature in the Illawarra region, contrasting sharply with the surrounding Hawkesbury Sandstone cliffs of the escarpment. The summit plateau and steep ridgeline are composed of hardened volcanic rock, evidence of a long-extinct volcanic system. From here, you can observe how ancient volcanic activity has shaped the land, leaving behind a legacy of lava flows and eroded remnants of an ancient volcano.
Geological Insights
Unlike the nearby sedimentary escarpment, Mount Kembla was formed by intense volcanic activity during the Early to Middle Jurassic (approximately 200 million years ago). At that time, the region experienced massive eruptions, with magma forcing its way through cracks in the Earth's crust, spreading thick lava flows across the landscape.
Historical geological records describe an enormous eruption near Mount Nebo, just south of Mount Kembla. This event sent lava flowing across the region, altering coal seams, covering valleys, and forming the volcanic highlands we see today. The basalt and latite rock capping Mount Kembla are remnants of these eruptions, now hardened into resistant layers.
However, not much of the volcanic history can be seen directly today. Over millions of years, erosion has worn away much of the volcanic rock, leaving behind only the more resistant remnants. The volcanic core is now hidden beneath layers of sedimentary rock, and only subtle features, like the ridge and plateau, remain as evidence of the once-mighty eruptions.
Streams such as American Creek and Dapto Creek have further shaped the landscape, cutting deep channels that expose layers of volcanic rock, coal seams, and ancient sedimentary deposits.
Logging Tasks
Take a photo of the stunning view from the summit coordinates (no spoilers of answers, please!).
Questions
Q1: Unique Feature
What geological feature makes Mount Kembla distinct from its surroundings, and how was it formed? Explain how volcanic activity shaped the mountain.
Q2: Extinct Volcano
Mount Kembla is an extinct volcano. Based on what you observe and learn at this location, describe how erosion and time have changed the volcanic landscape. Why might much of the volcanic history not be as visible today?
Logging Instructions
You may log your find immediately to maintain your trackable inventory and statistics. However, please submit your answers via email or Geocaching Messenger (DO NOT POST THEM IN YOUR LOG) within 10 to 14 days. Failure to comply may result in the deletion of your log. If you need assistance, feel free to reach out.