Rochdale Volcanic. Visitor from T'Lakes.
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Rochdale is well known as the home of the co-operative and Gracie Fields. It is a town with an industrial history, which is bordered to the north and east by the bulk of the Pennines. It is a multi-cultural town , which has a vibrant community spirit. In Broadfield Park, there is evidence that Rochdale has had visitors well before the industrial ages of the 19th and 20th centuries.
In the park is an erratic boulder, which is reputed to have come from the Coniston area. The boulder is made of andesite, which is basically a volcanic rock. Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet are common accessory minerals.Alkali feldspar may be present in minor amounts. Classification of andesites may be refined according to the most abundant phenocryst. Example: hornblende-phyric andesite, if hornblende is the principal accessory mineral. Andesite can be considered as the extrusive equivalent of plutonic diorite. Andesites are characteristic of subduction zones, such as the western margin of South America. The name andesite is derived from the Andes mountain range. Lava is molten rock that has been extruded onto Earth's surface. Before it reaches the surface, lava is called magma. Magma contains crystals, unmelted rock, and dissolved gasses, but it is primarily a liquid. Oxygen, silica, aluminum, iron, magnesium, calcium, sodium, potassium, titanium, and manganese are the primary elements found in magma, but other trace elements may be present in small amounts. Viscosity of lava, or its resistance to flow, is determined by its temperature and chemical composition. In general, hotter lava that is low in silica flows much more readily than cooler, high-silica lava. The composition and viscosity of magma determines both its eruptive style and the rock type that will be formed when it cools. The three main types of lava, named for the rock types that they form, are basaltic (for basalt), rhyolitic (for rhyolite), and andesitic (for andesite). Andesitic lava has a composition that falls in between that of basaltic lava and that of rhyolitic lava. Andesite is hence classified as an intermediate rock. Andesitic lava flows more readily than rhyolitic lava, but not as easily as basaltic lava. Eruptions are characterized by a mixture of explosive activity and lava flows. Such eruptions form composite volcanoes, built up of alternating lava flows and pyroclastic deposits (deposits of debris ejected from the volcano). This boulder originates from the Ordovican age, and the andesite is part of the Borrowdale Volcanic Group. The Borrowdale Volcanic Group is a group of igneous rock formations named after the Borrowdale area of the Lake District, in England. They are late Ordovician in age (roughly 450 million years old). It is thought that they represent the remains of a volcanic island arc, approximately similar to the island arcs of the west Pacific today. This developed as oceanic crust to the (present) north-west and was forced by crustal movement under a continental land-mass to the present south-east. Such forcing under, as two plates meet, is termed subduction. This land-mass has been named Avalonia by geologists. It is now incorporated into England and Wales and a sliver of North America. At that time the rocks that now comprise most of Scotland (and part of the northern Irish landmass) were not attached to Avalonia. They were separated by an ocean, called the Iapetus Ocean by geologists. The line of joining, or suture, is approximately under the Solway Firth and Cheviot Hills. In the Lake District, the junction between the early Ordovician series, Skiddaw Slate, and the Borrowdale In the English Lake District, the Borrowdale Volcanic Group is composed of lavas (mainly andesites), tuffs and agglomerates, along with some major igneous intrusions. These rocks of the Borrowdale Volcanic Group give rise to dramatic scenery. So, how did this fellow from the Consiton Fells get to Rochdale, as in years gone by there wasn't a bus or train to transport hi. The answer is the ice age, when this stone and many others were transported by the ice. A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare, and are carried by glacial ice, often over distances of hundreds of kilometres. At the time of the ice age, the ice field was going in a North West to South east direction. The park has parking nearby, and the path is also suitable for a wheelchair and buggies. To log the cache, please do the following : (1) As an option take a picture of you or your GPS with the erratic. (2) Please email me with the answers to the following: (a) Where is the erratic from. How far has it travelled? (b) What type of rock is it, and how was it formed? (c) What colour is it? (d) Can you see or feel any evidence on the rock itself of its journey as an erratic? (e) Using a compass, what direction in degress is the stone alined on, and to get back to where it came from how many degress would you need to + or -. Sources of information: Notice board in Broadfield Park.Broadfield Park website. Rochdale before Doomsday. Search of internet, such as souces like Wikepedia. My son who is currently doing geography at school.
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