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Virtueller Geocache
The Grose Valley from Govetts Leap Lookout

 Earth Cache at the Blackheath area of the Blue Mountains

von Roi Danton     Australien

S 33° 37.690' E 150° 18.680' (WGS84)

 andere Koordinatensysteme
 Größe: kein Behälter
Status: kann gesucht werden
 Zeitaufwand: 0:30 h   Strecke: 0.5 km
 Versteckt am: 24. Juli 2019
 Veröffentlicht am: 28. Juli 2019
 Letzte Änderung: 29. Juli 2019
 Listing: https://opencaching.de/OC15986
Auch gelistet auf: geocaching.com 

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große Karte

   

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Beschreibung    English

Note in advance: The original is an Earth Cache, here in Opencaching it is a virtual cache. However, I left the description like it is on Geocaching.com.

This Earth Cache is located at the Govetts Leap Lookout in the Blackheath area of the world famous Blue Mountains National Park.

Access the Earth Cache

The cache itself isn't difficult to do. To do this cache, park at the Govetts Leap Lookout car park (see Parking waypoint), walk into the direction of the lookout to GZ.

Please always be careful while attempting a geocache, also this Earth Cache. Be sure to stay on the tracks. There is no need to cross any safety fences or leave any walking tracks to obtain information or take photos.

Claiming the Earth Cache

Because a lot of people still use Garmin devices like the Oregon and the Colorado models with the paperless caching feature but the issue that listing text might be cut off, the questions you need to answer to log this cache are placed at the front. Make sure to read the rest of the information though. It may even have some answers.

To log the cache, answer the following questions and post the replies to me through my Opencaching profile page. You don't have to wait for a permission to log. If there is a problem I will contact you.

  1. Standing at GZ at the edge of the Grose Valley: What indications that the valley is still forming today can you see?
  2. At GZ you can find two quadrangular bricked memorial structures with two plates each. Out of what stone do you think these structures were made of?
  3. Along with the log please post a photo of you or you and your party at GZ showing some of the pretty scenery as well (but not spoilering the above questions).
  4. Optional: Please write in your log where you are from (to get an impression who is visiting the lookout).

Area and geology

At GZ you are looking into the Grose Valley. The area contains some of the most dramatic gorge and canyon landscapes of the entire Sydney Basin sandstone region. Charles Darwin described the Grose Valley as "stupendous... magnificent" when he visited in 1836.

The Grose Valley is a rugged valley. It has been formed by the Grose River, the headwaters of which are in the Mount Victoria area. The valley is located between the Great Western Highway and Bells Line of Road, the two major routes across the Blue Mountains. The majority of the valley falls within the Blue Mountains National Park.

The Bridal Veil Falls (also called "Govetts Leap", the name of the lookout, as "leap" is an old Scottish word for "waterfall") can clearly be seen from the lookout looking in a south-west direction. The waterfall is certainly not a very wide waterfall, but it’s the height (180 metres) and the impressive surrounding scenery that make it such a beautiful place on earth.

The geology of the area consists of Triassic (a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago to the beginning of the Jurassic Period 201.3 million years ago) sandstones and underlying Permian (a geologic period and system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago to the beginning of the Triassic period 251.902 million years ago) sedimentary rocks. From the GZ and also most other lookouts in the Blue Mountains you can see these typical formations - for more information please continue reading. At Govetts Leap Lookout a number of basalt-capped peaks dominate the area, notably Mount Banks and Mount Hay which you can see a bit further in the distance. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its iron-rich minerals into iron oxides and hydroxides.

The view from GZ is showing a typical erosion profile of the Blue Mountains. There is a relic plateau on top coming to an abrupt edge at a sandstone cliff. Below the cliff is a talus slope leading to the valley floor. This talus is in most places covered by vegetation and in turn, covers the softer rock that has undermined the sandstone above. The Burramoko Head sandstone in the upper and middle Grose gorges possesses weathering tendencies of breakage along vertical joints and has consequently yielded some of the sheerest cliff faces in the Blue Mountains.

It has taken 15 million years for the Grose River and its tributaries to carve out the Grose Valley through a combination of volcanic uplift and erosion. The river has eroded an extensive labyrinth of gorges and canyons through the Hawkesbury (upper) and Narrabeen (lower) group sandstones, exposing cliffs of commonly over 200 metres and up to 510 metres in height (Banks Wall).

But the Grose River did not do this alone - and it didn't take only 15 million years...:

Making a landscape - deposition and eruption

About 300 million years ago the local landscape was made up of even older, mixed rocks that had been changed by heat and pressure, buckled and folded.

Crustal rifting caused the area to sink until at times it was flooded by the sea. A long period of deposition into this depression followed. Rivers washed in sediments eroded from distant inland mountains and dying swamp vegetation piled up to form coal.

During the Permian Period mostly sandy and muddy sediments were deposited, followed by a massive thickness of sands, clays and pebbles into the Triassic. Then finer sediments were piled on the top of the sequence.

Deposition may also have occurred in the Jurassic and Cretaceous but if so, these later layers have been stripped away by erosion.

As the sediments were progressively buried beneath higher layers, they were compacted and changed into solid stone. The huge sedimentary structure is known as the Sydney Basin, and covers 64,000 square kilometres (some of it offshore).

Volcanic activity has also left its mark on the Blue Mountains. During the Jurassic, explosive volcanic vents punched holes up through the sedimentary layers of the Sydney Basin – some 200 of them, many in the Blue Mountains.

Then about 20 to 14 million years ago basalt lavas flooded across the landscape from multiple but unknown volcanoes.

Lifting and carving the mountains

The great pile of Sydney Basin debris (up to six kilometres thick) represents some 65 million years of accumulation.

The next step in making the mountains was when earth movements pushed up the Sydney Basin rocks (and also the Central Tablelands and more). These uneven uplifts raised a broad tableland that sloped gently from the highlands towards the coast with, in places, a sharper escarpment on the eastern edge.

Erosion accompanied the uplifts and is an ongoing process of stripping off the upper rock layers and carving all the valleys, canyons and gorges.

As earlier mentioned, Charles Darwin stood at Govetts Leap in 1836. He thought the puny stream below could not account for the prodigious valley, and surmised that the sea must have inundated the land and formed the gorges by coastal erosion. But he was wrong. All that was required for that stream to cut the Grose Valley was enough time, and enough floods.

Permission

Permission was granted from the NSW National Parks and Wildlife to place this Earth Cache in the national park. I learned that placing a "virtual cache" in NSW national parks does not require permission (see NSW Office of Environment and Heritage Geocaching policy), but Earth Cache regulations do, so I am happy that I asked.

References and further reading

Some text was taken from Grose Valley @ Wikipedia, Geology by Ian Brown and Govetts Leap lookout @ NSW National Parks and Wildlife Service. The map image was taken from Google Maps.

 

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Zusätzliche Wegpunkte   andere Koordinatensysteme

Parkplatz
S 33° 37.701'
E 150° 18.663'
Govetts Leap Lookout car park
Info Die zusätzlichen Wegpunkte werden bei Auswahl des Caches auf der Karte angezeigt, sind in heruntergeladenen GPX-Dateien enthalten und werden an das GPS-Gerät gesendet.

Bilder

Govetts Leap Lookout
Govetts Leap Lookout
Govetts Leap Lookout
Govetts Leap Lookout
Grose Valley overview (c) Google Maps
Grose Valley overview (c) Google Maps

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