Seven Mile Beach - Coastal Dune Formation EarthCache
Hidden : 5/10/2025
Difficulty:
3 out of 5
Terrain:
4 out of 5

Size: Size: other (other)

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Geocache Description:


Earth Science Lesson: The Dunes of Seven Mile Beach

Seven Mile Beach is a long stretch of sandy coastline that runs for just over 12 kilometres between the towns of Gerroa and Shoalhaven Heads in New South Wales. This beach is a great place to see how natural forces like wind, waves, and plants work together to shape the land, especially the sand dunes behind the beach. These dunes have been forming for thousands of years and are still changing today.

The sand that makes up the beach and dunes mostly consists of quartz grains. Quartz is a very hard mineral that resists breaking down, which means it stays as tiny grains for a long time. This is why the sand at Seven Mile Beach is usually light in colour and feels fine when you rub it between your fingers. Other minerals that are softer get worn away by waves and weather.

Dunes are formed when wind blows sand from the shore inland. As the wind slows down, it drops the sand, which starts to pile up. Over time, these piles grow into hills called dunes. Plants like spinifex grass and coastal wattle begin to grow on these dunes, and their roots help to hold the sand in place. This makes the dunes more stable and less likely to be blown away by wind. However, strong winds and storms can still erode the dunes, causing them to move or change shape.

If you look carefully at the dunes, you might notice layers of sand with slightly different colours or textures. These layers show times when conditions changed — maybe when the wind was stronger, or when different amounts of sand were moved by the wind and waves. You may also see ripples or small grooves on the surface of the sand, which indicate the direction and strength of the wind that shaped them.

The shape of the dunes can vary. Some might be steep, while others have a gentle slope. This depends on how strong the wind is and how much sand is available. These dunes act as natural barriers that protect the land behind them from storm waves and flooding. They also provide habitat for many native plants and animals that are adapted to living in sandy and salty environments.

Visiting Seven Mile Beach offers a chance to see these natural processes in action. This is part of what scientists call coastal geomorphology — the study of how the coast changes over time due to natural forces.

Seven Mile Beach was also the site of a historic aviation moment. In 1933, Sir Charles Kingsford Smith used the beach as a runway for the first commercial flight between Australia and New Zealand.

The diagram shows how wind (aeolian processes) moves sand from the beach inland by bouncing (saltation) and rolling (creep). When the wind slows near plants or rocks, sand builds up into dunes that slowly move as sand shifts from windward to leeward sides.

 

Logging Tasks

To claim this EarthCache, you must complete the following tasks during your visit:

1. Observe the Dune Layers

Walk to the base or side of a dune where natural erosion or foot traffic has exposed the sand. Describe:

  • Can you see layers in the dune? If so, are they different in colour or texture?

  • What might cause these layers to look different?

2. Dune Shape and Wind Effects

  • Describe the shape of the dunes near the posted coordinates. Are they steep, rounded, low, or sharp?

  • Look closely at the sand. Can you see ripples, grooves, or signs of wind action? What do these features suggest about the wind direction or strength?

3. Sand Texture and Composition

Pick up a small amount of sand (no removal). Rub it between your fingers.

  • Is the sand coarse or fine? Dry or moist?

  • Based on what you feel, what kind of minerals might the sand be made from?

5. Photograph Requirement

Take a photo of yourself or a personal item (e.g. GPS, hat, or notebook) with the dunes and Seven Mile Beach in the background. This proves you visited and observed the site in person.

 References

Websites

Book

Newspaper Article

 

Logging Instructions

Please submit your answers via Geocaching Messenger or email within 10–14 days of logging your find. Logs that do not include answers to the required tasks may be deleted. Please do not post your answers in your log

 

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