| The Harrietville 5 - The Earth Cache
The Harrietville 5 is a series of 5 caches, each of a different type. One Traditional, One Multi Cache, One Unknown, One Letterbox and One Earthcache. The town of Harrietville was chosen as it is one of my favourite little towns and I noticed that it did not have a cache placed in it at the time.
This is the Earth cache, read the information below and visit the site to get the required information. You must email me the answers to the questions to verify your "Found It" log.
Take a good look around you, the little town of Harrietville is nestled on the banks of the Ovens River, at the foot of Mt Feathertop's western slope in a picturesque location. Geology formed the great mountains you see before you. Geology created the rivers that you can hear flowing in the back ground. Geology even created the whole reason for the little town you're standing in!
But first, a geology lesson.
Around 520 million years ago, the area where you're standing was deep below the ocean. Dotted along the ocean were high volcanoes, similar in appearance to the current Western Pacific islands. They spewed forth basalt lavas which settled on the ocean floor as basalt rock. None of this can be seen here, but it is visible in the Howqua Valley of Victoria. Over the next 80 million years or so, the ocean floor was covered with sand, which over time turned into the sedimentary rock, sandstone. During this time, a large chain of volcanoes formed which erupted further basalt lava into the ocean.
Around 440 million years ago several small tectonic plates began to collide. The basalt and the sandstone were forced up into huge mountain ranges or it was forced down deep into the bowels of the earth. The sandstone that was forced down into the earth was super-heated to temperatures above 650 degrees Celsius and metamorphosed to become slate, before being forced back up to the surface again. Slate is very common around the high country, just take a walk from here up to Mt Feathertop!
The volcanoes of the Silurian and Devonian period (440 - 360 million years ago) in this area were particularly active and explosive. Granite was formed from magma during this period and large amounts of ash covered the land. Later erosion of the land saw the granite exposed as rocky peaks that are quite evident at places like The Cathedral at nearby Mount Buffalo. By the end of the Devonian period (360 million years ago) much of what is now South Eastern Australia was a towering mountain range with peaks in excess of 3000 meters above current sea levels. These mountains actually had nothing to do with the current day mountains that we see now, but they formed huge valleys, with rivers and lakes. Sediments from these lakes formed at the bottom as a reddish coloured sandstone. These can now be seen on the high plateaus of the Avon Wilderness area in Victoria.
Over the next 200 million years or so, the mountain range was part of the super-continent Gondwana. Gondwana existed near the south pole and so during the global ice age around 250 million years ago, large ice sheets eroded away the mountain ranges until all that was left was a low-lying plain.
Around 130 million years ago, in eastern Gondwana, magma deep below the surface began moving upwards. It caused an uplifted, dome-shaped plateau. which possibly rose above 2000 meters by about 100 million years ago. A rift valley began to form along the top of this plateau because the crust was being stretched and the valley floor dropped along the fault line. Eastern Gondwana split along this rift valley, with New Zealand drifting easterly away from Australia and the Tasman Sea filling the gap. The Australian Alps, with their steep eastern sea-side and their gentle inland slopes are what is left of the original plateau.
Over the last 50 million years, basalt lava has continue to erupt occasionally over the alpine area. The lava came out of small volcanoes and flowed across the landscape, forming flat landscapes in the high plains, such as the nearby Bogong high plains. Dykes and pipes of igneous rock intruded into the layers of sandstone forming many quartz reefs.
Rivers and streams formed and etched through the weaker rocks, forming huge valleys (like the one you're standing in). Occasional upheaval of mountains through tectonic movements would occasionally alter the course of these rivers, or reverse their flow completely, continually changing the shape of the land until it exists as you see it today.
Now for the questions that you will need to email to me to claim the smiley.
Q1. How does the town of Harrietville owe its existence to the formation of the quartz reefs during the last periods of crustal upheaval?
Q2. Nearby (still in the same park) there is a strange looking monument built in 1961, what is the colour of the rock that forms the base of this monument and from what geological-age do they come from?
Q3. Also nearby (also still in the same park) is a statue of someone searching for an elusive type of metal. What type of method are they using and please explain the properties of the metal that they are searching for that makes this method effective.
Once you have the answers, you may claim the smilie. But you must email me the correct answers to the above questions within a week, or else your log will be deleted.
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