The 12 Days of Cachemas (TDOC24) is a series of caches placed across Victoria to celebrate Cachemas in July in 2024. The series is a joint initiative of Geocaching Victoria and the local community to release caches in a different category each day across the state. We hope you have as much fun finding this series, as we all had placing them. A geocaching list of the full series is available at https://coord.info/BMDGW0P
On the second day of Cachemas, Signal gave to me,
two earthcaches,
and a wherigo up in a tree.
Geocache Description
Logging Tasks
Click on ‘Message this owner’, or send an email here with answers to the following logging tasks:
- At GZ, eyeball the opposite bank across the river. Do you think it is higher, the same as or lower than the bank you are standing on?
- You are standing on top of a 5-6 metre high bank, is this a result of seismic tilting or as a result of erosion?
- What is erosion?
Please include a photo with a personal/identifying item in your log.
The Lesson
The Murray River’s course has been shaped by fascinating geological events over thousands of years. Let’s delve into this remarkable story:
- The Cadell Tilt and Seismic Activity:
- Approximately 60,000 years ago, a minor uplift in the Earth’s crust occurred, significantly impacting the Murray River and associated streams.
- This event is considered one of the world’s most spectacular examples of seismic activity altering a river’s course.
- Around 45,000 years ago, the Murray originally flowed westward through the region where Mathoura now stands.
- Scientists believe that the uplift, known as the “Cadell Tilt,” began about 20,000 years before this major shift.
- When the large block suddenly rose, the river had nowhere to go, leading to significant changes.
- The Weir and River Diversion:
- Initially, a weir formed, holding back both the Murray and Goulburn rivers. This caused substantial flooding in two large areas.
- Eventually, the Murray changed direction, flowing north. Most of its water now passes through what we know as the Edward River.
- Simultaneously, the northern lake continued to fill, and silt jetties formed across it toward Barmah.
- The Goulburn River also played a role, filling Lake Kanyapella, which extended from south of Moira to the area where Echuca stands today.
- Ancient Landscape and Vegetation:
- The landscape during this period was vastly different from today.
- There were no extensive forests, and notably, no river red gum trees existed.
- Pollen evidence suggests that red gums only invaded the area around 6,000 years ago.
- Tree ferns grew along the Murray during this time.
- River banks consisted mainly of open woodland and grassy plains, while higher ground west of the uplift was arid.
- Glacial Influence:
- Until the end of the last ice age (approximately 20,000 years ago), glaciers covered the ranges near Mount Kosciuszko.
- These glaciers contributed meltwater, which fed the Murray River for most of the year.
- Edward River Formation:
- Once the Edward River established its course, the northern lake began to drain, transforming into a series of wetlands and swamps.
Our planet is dynamic. Many forces act on the surface of the earth continually renewing and reshaping it. Earthquakes, volcanic eruptions, weathering and erosion to name but a few.
Weathering and erosion are the key processes responsible for reshaping earth’s surface.
- Weathering is the action by which a number of agents, most involving water in one form or another, break down pre-existing rock into sediments.
- Erosion is the process of transporting the weathered material, eventually depositing it in a new location or environment.
Moving water has the ability to weather and erode rock. This often occurs by a process known as corrosion or simply abrasion. Corrosion occurs when sediment, including sand-sized or smaller particles, are carried by moving water. As these particles pass by pre-existing rock, they wear it down over time. Rivers and streams can be very powerful weathering and erosion agents. Consider the mouth of the Murray River which occasionally gets blocked due to deposition of sand and gavels being transported by the river.
In summary, the Murray River’s journey reflects a dynamic interplay of geological forces, river shifts, and changing landscapes over millennia.