Cherrybrook Natural Arch
As this is an Earthcache, there is no physical container to find.
A lovely walk through a small part of the Berowra Valley Regional Park will lead you to the extensive rock platforms of Refuge Rock and then down to another of Mother Nature’s works of art, a natural rock arch. Explore the area and marvel at the geology you discover. Read the Earth Science Lesson to learn how these natural arches are formed. Then, to claim a find, complete the logging tasks as outlined below.
Getting There:
The best place to park is at the end of Trevors Ln, Cherrybrook (see parking waypoint). The walk passes the ‘Berowra Valley Regional Park’ sign and follows the fire trail beside/behind the houses. You'll pass around a gate and after a few more steps, arrive at an intersection with another fire trail, (Firetrail trailhead point). Turn left here. Navigate the fire trails to the Refuge Rock reference point then turn right and follow the track to the Track reference point. From there, it’s just a short walk in.
When you arrive near GZ be careful of the geokids as there are unfenced cliffs nearby. At the Narrow Channel Path reference point, you will see a long, narrow channel path leading down between the rock ledges, (see photo below).
Narrow Channel Path reference point
Follow this path. At the end, swing round to your right 180° and find another quite narrow channel path between the rock faces, leading down to the natural arch and GZ where you can make your observations. If you’re uncomfortable about going through this second channel, you can take the track down that goes right around the rock outcrop.
The walk in to the natural arch is approximately 1km and will take around 15min-20min to complete.
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Logging This Earthcache:
To claim a find, you will need to physically visit the Cherrybrook Natural Arch at GZ, read the information contained in the Earth Science Lesson below then complete the following logging tasks and send me your responses. Include the earthcache title in your correspondence. You can log your find immediately, however, I ask that your responses to the logging tasks be sent to me as soon as you are able to. I read all messages/emails to verify the responses and will send a confirmation message/email back to you. If your correspondence is not received within a timely manner of your online log, your log may be removed. There is no need to send me photos. Just upload any photos with your online log.
Tasks:
1) From GZ, looking up at the natural arch and rock walls either side and to the back, describe in as much detail as you can, the panoramic view in front of you.
2) Estimate the span of the arch, in a straight line, between the points where the arch touches its base. For example….
3) Feel the natural arch from underneath. Looking from below, the left side is probably the best. Describe the texture, grain size and any other characteristics of the sandstone here.
4) From what two types of rock are most natural arches formed? (See lesson)
5) What is the relatively harder stratum above an arch called? (See lesson)
6) Optional - Take a photo of you and/or your geocaching name and/or your GPS device with either of the two narrow channel pathways that lead to the Natural Arch. Brownie Points if you have all four items in the one photo lol.
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Earth Science Lesson
Moon Hill, Yangshuo, China
A natural arch is a rock formation where an arch has formed with an opening underneath. Natural arches commonly form where inland and coastal cliffs are subject to erosion from weathering, rivers and the sea.
Most natural arches are formed from sandstone or limestone rock with steep, often vertical, cliff faces.
The formations become narrower due to erosion over geological time scales (millions of years). The softer rock stratum erodes away creating rock shelters, or alcoves, on opposite sides of the formation beneath the relatively harder stratum, or caprock, above it. Over time, the alcoves continue to erode further into the formation eventually meeting underneath the harder caprock layer, thus creating an arch. The erosional processes exploit weaknesses in the softer rock layers making cracks larger and removing material more quickly than the caprock. The harder caprock itself continues to erode after an arch has formed, which will ultimately lead to it collapsing.
There are many examples of natural arches in Australia. Here are three:
Grand Arch, Jenolan Caves, NSW
What is often missed on a visit to the caves is the huge rock arch called the Grand Arch that all vehicles must pass through on their way to the Visitor’s Centre and car park. The arch was once the entrance to a large limestone cavern. Due to water seepage, the cave collapsed many centuries ago, but the arch remains. The Grand Arch is the largest open cave in Australia. It is 24 metres high, 55 metres wide and 127 metres long.
Grand Arch, Jenolan Caves, NSW
London Arch, Great Ocean Rd, Victoria
Before 1990, London Bridge was exactly that – a bridge that connected the arch of land to the mainland. It got its name from its likeness to its namesake, before being later known as the London Arch. This is all due to part of this massive structure collapsing into the ocean on the 15th of January 1990, leaving behind a chunk of land isolated from the mainland. However, it didn’t just leave the land isolated but the collapse also left two sightseeing tourists stranded. They then had to wait many hours before they could be rescued by a helicopter.
Before and after the collapse
The Archway, Northern Territory
This natural arch near the border of Kakadu National Park dramatically illustrates the erosion that has carved out the many rock features of the Arnhem Land sandstone plateau. It is the largest of hundreds of arches and caverns scattered throughout this ancient countryside. Being on Arnhem Aboriginal tribal land, it is not accessible to the public by land. The only way to see it is by taking a helicopter or aeroplane trip out of Jabiru Airport in Kakadu National Park.
The Archway, NT
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China
The largest natural arch, by a significant margin, is the Xianren Bridge in China, with a span of approximately 122 metres. It is known locally as the “Fairy Bridge”. Because of its remote location, accessible only by a three-hour rafting trip, it was not discovered until recently and remains relatively obscure.
The United States
Arches National Park in Utah has the highest concentration of natural stone arches in the world. There are over 2,000 documented arches in the park, plus pinnacles, balanced rocks, fins and other geological formations.
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*** Check out the stunning photography off this YouTube video that shows the ten most beautiful natural arches in the world:
Top 10 Natural Arches in the World
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This earthcache is located on land under the control of the NSW National Parks and Wildlfe Service. Please click on the following links to access further information about visiting National Parks:
Safety in NSW National Parks
Alerts for NSW National Parks
Information about NSW National Parks
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References: Wikipedia – Natural Arches; Australia For Everyone Website; Sightseeing Tours Australia; Naturalarches.org; WildWalks; Kakadu Tours; victorianplaces.com; YouTube - Top Ten Natural Arches In this World created by Tushar Dutta
FTF Honours
Jackscruff
An Educated Earthcacher
Did you know that NSW has a geocaching association? Geocaching NSW aims to enhance and improve the activity of geocaching and holds regular events where geocachers meet to enjoy their common interests. Visit the association website here.