Glacial Boulder - Cannock Chase
Cannock Chase is an Area of Outstanding Natural Beauty renowned for its lowland heath and rich biodiversity. In terms of its geomorphology, Cannock Chase comprises an undulating plateau of 150–250m elevation that stands proud of the surrounding valleys due to the combined influence of tectonic processes (earth movements) and surface denudation (by wind, water and ice). Tectonic processes resulted in the local uplift of Triassic sandstones. These rocks are harder and more resistant than the mudstones of the surrounding area and subsequent differences in the rates of weathering and erosion have further accentuated the relative relief. The episodic growth and retreat of the British Ice Sheet over the last 2 million years has had a dramatic impact on the landscape. Whilst the Glacial Boulder demonstrates the ability of glaciers to transport material long distances, glacial meltwater has generated the most impressive landforms. Both the prominent valley cutting through the heart of the Chase as well as a series of deeply-incised channels around the northern perimeter of the Chase highlight the erosive power of glacial meltwater.
At other times, the Chase was free of glacier ice but was still subject to cold conditions similar to northern Canada today. The development of permafrost promoted surface drainage when snow melted during the brief summers. This, in combination with the influence of freeze-thaw weathering, explains the dry valleys and the dissected nature of the plateau. The asymmetric cross-sections of valleys like the Sherbrook are also characteristic of these regimes. South-westerly winds would have caused snow to accumulate on east-facing slopes. Melting of these snow banks in summer caused small landslides that pushed the stream to the opposite side of the valley, undercutting the opposite bank and generating a steeper west-facing slope.
Set upon a pedestal of Triassic pebbles, the boulder is of Granite which is out of place here on the Moorlands of South Staffordshire, there being no granite outcrops anywhere in the Midlands. The boulder has been matched however, to the intrusive rock outcrop at Cniffel in Dumfries & Galloway, which is over 170 miles (280km) away from the Chase in the Southern Uplands of Scotland. This granite 'erratic' is marked on the OS map as the "Glacial Boulder", which gives some idea how it got here. The boulder was ripped from its parent mountain sometime during the last Ice-Age, and was transported by glacial action to its present location, the journey perhaps taking ten-thousand years during which the edges of the rock were worn down, giving its present rounded appearance.
To log this cache please email us with answers to the following. Do NOT put them in your logs please.
1.Describe the texture and colours of the boulder
2.Estimate the size. (Length x width x height)
3.We would also like a photograph of yourself or your GPS with the boulder in view. This can be uploaded to the cache page but is optional. We are, however, happy for you to log the find without waiting for confirmation. Please adhere to ALL requirements or, as stated above, non qualifying logs WILL be removed.
Enjoy!