Celebrating my 100th cache placed.
There was previously an Earthcache featuring this rock GC2176E but was archived in 2019..Originally placed 20 Nov 2009. Racked up 785 finds and 535 photos and 43 fav points. Permission given by junglehair to use most of the scientific descrition on the archived cache page.
Otiginal Cache by Équipe Papou Team, adopted by junglehair
Glacial erratic
Definition: An erratic is a boulder transported and deposited by a glacier having a lithology different than the bedrock upon which it is sitting on. A glacial erratic is a piece of rock that differs in colour, mineral make up, mineral infusion veins, from the size and type of rock native to the area on which it rests. "Erratics" take their name from the latin word "errere", and are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock (16,500 tons) in Alberta, Canada. Geologists identify erratics by studying the rocks surrounding the position of the erratic and the composition of the erratic itself. Erratics were once considered evidence of a massive flood approximately 10,000 years ago, similar to the legendary floods described in the texts of ancient civilizations throughout the world. Ancient legends of an epic flood come from many cultures including Mesoamerican, Sumerian (Epic of Gilgamesh), Hebrew (Old Testament) and Indian culture. In the 19th century, many scientists came to favor erratics as evidence for the end of the last glacial maximum (ice age) approximately around the same time., rather than a flood. Geologists have suggested that landslides or rockfalls initially dropped the rocks on top of glacial ice. The glaciers continued to move, carrying the rocks with them. When the ice melted, the erratics were left in their present locations. Erratics are useful indicators of patterns of former ice flow. Of course there are other equally credible explanations as to the time frame of the events that took place in this country. possibly an ice age following the flood.
This cache
The glacial erratic in question is composed of 2 fairly irregular polygons, one being of very impressive size (10m long x 7m thick x 6m high) while the second one is smaller (5m long x 2m thick x 3m high), for an approximate total volume of some 30 cubic metres and a weight of some 400 to 450 tonnes. Errarics usually have features: rough edges, non smooth surfaces. Rocks that the glacier was carvong away hve smooth surfaces with gouge marks where other material has worn it away as the ice moved. Some erratics are more smooth than others due to where in the ice they travelled. At the bottom, in the middle, or at the top. When the ice finally melts or retreats up the mountain these rocks are left behind as deposits. It is most likely that it was deposited by one ice field covering the region during the last glacial era. New Zealand was of low enough latitude for its high mountains to be heavily glaciated during this Ice Age. Great rivers of ice flowing from the Southern Alps merged on lower ground to form local ice sheets that deposited thick beds of moraine; glacial erratics are part of this moraine and were deposited when glaciers retreated.
In order to log this EarthCache, you must answer the following questions and observations. :
1 : This glacial erratic has split and a smaller block rests against the larger block. What is the angle of the fracture? Using the true horizon as the base of the angle. See cache photo.
2 : Compare the rock in the glacial erratic with the bedrock on which it sits? Do you see differences in the glacial rock and the rock it sits on? Why do you think there are these differences?
3 : By observing the erratic rocks edges and surfaces, Give a reason for your opinion on wether they were at the bottom of the ice or floaters on top.
4: Photo. With your online log, post an interesting picture by the rock. You can choose if you want to be in the photo.
Message to CO your observations. I usually respond within 24 hours. You can log at same time.
Parking. I have not included any waypoints for parking as you most probablly wont get close to Queesntown Gardens to park there due to parking demand so do expect to do a bit of walking before you enter the Botanic Gardens. Take your time finding other traditionals in the Gardens. There are two main entrances to the park. Lower entry is on the lake front at Church St & Marine Pde corner where there is a memorial arch. Top entrance is on Park Street.
Tracks and Trails. Within the Gardens you will find a variety: ashpelt, gravel, pine needle covered rock, stairs. So do take care. Also there may be flying discs from those playing disc golf.
Photography hint. Best time for taking photos is autumn (or called Fall). Up by the duck pond is a stone bridge. Best early morning to get good reflections and light up the bottom of bridge.