![]() The Pacific plate is moving north at about 5 cm per year. Of the faults the riddle Alaska, best known is the subduction trench. Finally, the Alaskan range formed when the current Pacific plate began to subduct underneath the young continent.īrooks mountain range, seen from the coastal plain, north Alaska Later, a new plate fragment hit, and the White Mountains formed in the same way, separated from Brooks by the Yukon valley. This collision formed the Brooks mountain range 150 million years ago, and it largely closed off the connection between the Pacific and the Arctic ocean. Over the next two hundred million years, a tectonic plate drifted north and hit the shallows. 400 million years ago, the sea between the Pacific and the Arctic ocean was shallow, an extension of an older mountain range reduced to small islands and submerged land. How little times have changed, with another Crimean war and a North Atlantic trade war in progress! The geology of Alaska also derived from Asia. ![]() That prospect alarmed both Russia and the USA, so the purchase suited them both. At the time Russia was recovering from the Crimean war and it was expected that in any resumption of hostilities Britain would capture Alaska. That is true politically, with the purchase from Russia in 1867. And still it came as an early-morning surprise.Īlaska is a late addition to North America. The rumblings had indeed given plenty of warning that something could be brewing. And now, Alaska is back in the news: after months of rumblings across the state, and a larger earthquake in the normally earthquake-free zone in the north, a big one hit the most populated area of the state. Living here requires -and builds- character. But to live there requires coping with everything the earth can throw at you, from the certainty of winter to the suddenness of an earthquake. There are volcanoes to admire (from a safe distance). There are the mountains and the wilderness, beautiful to see but harsh and unforgiving. There is the wonderful ocean, teeming with life in an abundance (though not colour) that puts the tropics to shame. ![]() Hazards seldom come alone.Īlaska has it all. Furthermore, these are seldom flat deltas -an active earth builds relief, and relief with shaking gives the risk of landslides. And as subduction zones tend to be coastal, there is an added danger of tsunami activity. It is not a surprise that people in volcanic regions need to be earthquake-aware. Indeed, volcanoes are like acne: they are symptoms of the turmoil beneath. And the weight of the mountains can fracture the earth near them. Sometimes the volcanoes grow on top of those ranges, sometimes they are distinct. And the subducting plate pushes up the continental plate it subducts under, forming its own mountain ranges. The volcanoes may appear 100 km from the subduction region. The earthquakes are close to the subduction trench and the volcanoes are further down, where the subducting plate reaches the depth where melt can occur, with the molten rock percolating up. Here, of course, the earthquakes and volcanoes do not coincide. In contrast, a subduction zone really goes for it. ![]() A spreading centre can just push the crust aside, with minimal earthquake activity, but still not entirely silent. ![]() Volcanoes require vertical movement and earthquakes (by and large) are horizontal: the two are not identical, but to get a volcano you need a vertical path, and to get that you need to move crust sideways. Where there are volcanoes, there are earthquakes. ![]()
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