Yanchep National Park is located around 50km north of Perth and is accessed from Wanneroo Road. The Park is open between 9am and 5pm (entry fees apply), and it is a great place to spend the day and explore the various walking trails, spot some native animals and learn about the culture and history or the Nyoongar people of WA’s South-West. The park is also home to many limestone caves.
Crystal Cave is one of the more than 500 caves located in the park and is open to visitors. Crystal Cave 45-minute tours are run daily subject to availability at 10:30am, 11:30am, 1pm, 2pm, 3pm. You need to book onto a tour at the McNess House Visitors Centre at least fifteen minutes before the tour commences.
Please refer to the Yanchep NP web site for current park entry fees, Crystal Cave ticket prices and further information on other activities in the park.
Regional setting
Limestone deposited as marine sediment about 600,000 years ago underlies much of the Yanchep area. This limestone formation is quite shallow and is located on sand.
Formation of Crystal Cave
Crystal Cave is a “stream cave”. It started as wide, low chambers carved in the limestone by weakly acidic underground water from a stream. The chambers gradually continued to widen until the chamber walls could no longer support the weight of the roof, which then collapsed to form a cave.
Cave decorations
Inside the cave, the waxy looking growths of calcite (calcium carbonate) are the results of slowly dripping water. Mildly acidic water, mainly from rainfall, percolates down through the limestone, dissolving calcium carbonate as it goes. When this solution enters the cave, each drop of water leaves behind a minute deposit of calcite on the roof, then as it drops, more calcite is released on contact with the floor. From these tiny drops the ornate decorations of the cave slowly build up.
Some of the most common types of cave formations are:
Stalactites and stalagmites
Water seeping into a limestone cave drips from the ceiling and leaves calcite forming thin, hollow tubes, known as straws. Over time, water begins to flow along the outer edge of the straw, depositing calcite, making the icicle shape of a stalactite. They are found hanging from the ceiling of caves, or hanging off other formations.
Water dripping from the ceiling of a cave (or from a stalactite) also deposits calcite on the floor, creating a stalagmite from the ground up. They are found on the floors of caves, often directly beneath a stalactite.
When stalactite and stalagmite eventually join up, they form a column.
Stalactites and stalagmites are often confused. Here's an easy way to remember the differences between them:
Stalactites hold tight to the ceiling.
Stalagmites might grow up to the ceiling one day.
Shawls
Water running down a limestone cave wall or along a ledge will deposit calcite into delicate draperies, also known as curtains or shawls. Shawls can be found hanging out from walls, ceilings or other formations. They look like folded fabric and can vary in size. Shawls that have coloured stripes are sometimes called “cave bacon”. These coloured stripes are due to the presence of minerals (like iron oxide) or tannin (from plants) in the water.
Helictites
Helictites are formed in caves when water under pressure is pushed through a limestone wall, depositing calcite on the other side. They are found in the walls and ceilings of caves and also can be found growing off stalactites. Helictites seem to defy gravity. They usually come out from cave walls horizontally, can twist and turn or grow very straight and long.
Tasks
To log this cache, you will need to email me your answers to the following questions:
1) Inside Crystal Cave, what can you see that indicates that the cave is quite shallow?
2) In the Pantheon Chamber, observe the stalactites that are located above where the stream used to flow. Describe their shape and offer a possible explanation (see Q2 photo in Gallery).
3) What is used to determine if the cave is safe to enter?
Please email me your answers and I will contact you if I have any issues with them. You do not need to wait for permission to log this Earthcache.
I hope that you enjoy learning about the caves of Yanchep National Park!
Sources
DPaW - Yanchep NP information panels at Crystal Cave
http://www.caverntours.com
Congratulations to bella at waggy for FTF!