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Staffa ((スコットランド・ゲール語:Stafa),〔("Staffa" ) Sabhal Mòr Ostaig. Retrieved 27 July 2008.〕 ) from the Old Norse for stave or pillar island, is an island of the Inner Hebrides in Argyll and Bute, Scotland. The Vikings gave it this name as its columnar basalt reminded them of their houses, which were built from vertically placed tree-logs.〔Murray (1973) p. 44〕 Staffa lies about west of the Isle of Mull. The area is 〔This is Haswell-Smith's estimate. Keay (1994) states 28 ha.〕 and the highest point is above sea level. The island came to prominence in the late 18th century after a visit by Sir Joseph Banks. He and his fellow-travellers extolled the natural beauty of the basalt columns in general and of the island's main sea cavern, which Banks renamed 'Fingal's Cave'. Their visit was followed by those of many other prominent personalities throughout the next two centuries, including Queen Victoria and Felix Mendelssohn. The latter's ''Hebrides Overture'' brought further fame to the island, which was by then uninhabited. It is now in the care of the National Trust for Scotland.〔 ==Geology and pre-history== In prehistoric times Staffa was covered by the ice sheets which spread from Scotland out into the Atlantic Ocean beyond the Outer Hebrides. After the last retreat of the ice around 20,000 years ago, sea levels were up to lower than at present. Although the isostatic rise of land makes estimating post-glacial coastlines a complex task, around 14,000 years ago it is likely that Staffa was part of a larger island, just off the coast of mainland Scotland, which would have included what are now Mull, Iona and the Treshnish Isles.〔Murray (1973) p. 69〕 Steadily rising sea levels then further isolated this little island, which is entirely of volcanic origin. It consists of a basement of tuff, underneath colonnades of a black fine-grained Tertiary basalt, overlying which is a third layer of basaltic lava without a crystalline structure. By contrast, slow cooling of the second layer of basalt resulted in an extraordinary pattern of predominantly hexagonal columns which form the faces and walls of the principal caves.〔 The lava contracted towards each of a series of equally spaced centres as it cooled and solidified into prismatic columns, a process known as columnar jointing. The columns typically have three to eight sides, six being most common. The columns are also divided horizontally by cross joints.〔Mitchell, Colin and Mitchell, Patrick (2005) ''Landform and Terrain: The Physical Geography of Landscape'' Brailsford Press. ISBN 1-904623-56-5 (3.pdf )〕 These columnar jointed sections represent the tops and bottoms of individual lava flows. Between these sections lie regions of much more chaotic jointing, known as the entablature. The origin of the entablature is unknown, but could be due to flooding of the lava flow, causing much more rapid cooling, or the interaction of stress fields from the two regions of columnar jointing as they approach one another.〔Phillips et al. (2013) ''The formation of columnar joints produced by cooling in basalt at Staffa, Scotland'' Bulletin of Volcanology 75:715〕 Similar formations are found at the Giant's Causeway in Northern Ireland, on the island of Ulva and at Ardmeanach on the Isle of Mull.〔Keay & Keay (1994) p. 894〕 Grooves in the roof of MacKinnon's cave indicate either a pyroclastic flow or a series of eroded ash falls in the rock above the columnar basalt.〔("To Staffa with Ladder" ) (September 2006) ''Grampian Speleological Group Newsletter'' Number 128. Retrieved 9 September 2008.〕 The 'Staffa Group' is the name given to the series of olivine tholeiite basalts found in the vicinity of Mull which erupted 55–58 million years ago.〔Bell, B.R. and Jolley, D.W. (1997) ''Application of palynological data to the chronology of the Palaeogene lava fields of the British Province: implications for magmatic stratigraphy''. Journal of the Geological Society. London. Vol. 154, pp. 701–708.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Staffa」の詳細全文を読む スポンサード リンク
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