An elderly resident who has sadly passed away but who had lived on Southgate all of his life recorded that there had been a stone in the centre of the road at the junction of Hull Road and Southgate where it had acted as a boundary marker. This gentleman remembered the stone being dragged across Southgate to the side of the road by two large carthorses. This large stone is a glacial erratic. It is now on display in a small landscaped area with its own information plaque.
A glacier is basically an accumulation of snow that lasts for more than a year. In the first year this pile of snow is called névé. Once the snow stays around for more than one winter, it's called firn. As more and more snow piles up over the years, the weight of the snow on top starts to compress the snow on the bottom. This compression turns the snow to ice. The compression of the glacier continues for dozens, hundreds or even thousands of years, adding more and more layers on top and adding even more weight. The ice eventually gets compressed so much that most of the air is forced out of it.
Eventually, the glacier becomes so heavy that it starts to move. There are two forms of glacial movement, and most glacial movement is a mixture of both:
Spreading occurs when the glacier's own weight becomes too much for it to support itself. The glacier will gradually expand and "spread out" like cookie dough baking in the oven.
Basal slip occurs when the glacier rests on a slope. Pressure causes a small amount of ice at the bottom of the glacier to melt, creating a thin layer of water. This reduces friction enough that the glacier can slide down the slope. Loose soil underneath a glacier can also cause basal slip.
As they move, glaciers erode or wear away the land beneath and around them. Glaciers carry great amounts of soil, rock, and clay.
Glacial erratics are stones and rocks that were transported by a glacier and then left behind after the glacier melted. Erratics can be carried for hundreds of kilometres and can range in size from pebbles to large boulders, some of which can be the size of houses. Scientists sometimes use erratics to help determine ancient glacier movement by establishing the type of rock the erratic is made of and tracing it back to its origin.
How to claim the cache
In order to claim this Earthcache you will need to answer the following questions and e-mail them to the CO via the link at the top of the page. An optional photo of yourself or GPS device at GZ would be much appreciated.
1. Briefly, what is a glacial erratic?
2. What date was the erratic moved to the verge of Southgate?
3. Describe the colour and texture of the erratic.
4. Using your observations tell us which of the three main types of rock is this erratic; Igneous, Sedimentary, Metamorphic?
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