Surface and bedrock topography of the Mýrdalsjökull ice cap, Iceland: The Katla caldera, eruption sites and routes of jökulhlaups
Surface and bedrock topography of the Mýrdalsjökull ice cap, Iceland: The Katla caldera, eruption sites and routes of jökulhlaups
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冰岛米达尔斯冰盖冰盖的表面和基岩地形：卡特拉火山口、冰峰喷发地点和路线
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发表时间：
2000
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通讯作者：
Magnús T. Guðmundsson
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作者：
H. Björnsson;F. Pálsson;Magnús T. Guðmundsson
无线电回波探测显示Mýrdalsjökull冰帽下有一个大火山口。火山口环绕面积100公里，深600至750米，最高边缘达到1380米。三个主要的出口冰川侵蚀了火山口边缘300至600米深的裂口。火山口底部的北部在800米以下，面积为25公里，比南部更光滑，更深，其特征是冰下脊和个别山，从海拔750米到1100米左右。许多山脊从火山口向外辐射，但是没有一个是向南的。一个山脊向西指向邻近的火山Eyjafjallajökull，另一个山脊从火山口的东边缘向东指向E。山脊也从火山口边缘向西北、西北和东北方向辐射。一个线性的凹陷，被陡峭的斜坡所包围，200-250米深，1.5公里宽，向东北走向火山裂缝eldgj<e:1>。在过去的1100年里，火山口有20次喷发的记录，都造成了灾难性的jökulhlaups。在过去的四个世纪里，火山爆发发生在单一的喷口和火山裂缝上，它们的走向既有东西向的，也有南北向的。我们认为，上个千年（公元1755年）最大的一次喷发发生在一条从go - abunga向东延伸的几公里长的裂缝上；以及1823年和1918年在Háabunga东部边缘向北突出的山脊上的喷发。目前，融水从火山口内60公里的区域向东南方向流下Mýrdalssandur。在历史上记录的20个jökulhlaups中，除了两个之外，其余的都走了这条路。火山口内约20公里的区域向西南方向排水，向下延伸至Sólheimasandur。据了解，历史上有两个jökulhlaups沿着这条路到达Jökulsá <e:1> Sólheimasandi。第三条路线是向西北进入弗雷姆里·埃姆斯特鲁<e:1>和Markarfljót河，这条路线是公元前1600年由史前的jökulhlaup所走的。现在，冰川表面上的几个直径0.5-1公里的小坩埚显示了地热活动。融水积聚在两三个这样的大锅下面，经常以小jökulhlaups的形式排出。
Radio echo soundings have revealed a large caldera beneath the Mýrdalsjökull ice cap. The caldera encircles an area of 100 km , is 600 to 750 m deep and its highest rims reach 1380 m a.s.l. Three major outlet glaciers have eroded 300 to 600 m deep breaches into the caldera rim. The northern part of the caldera floor, where an area of 25 km is below 800 m, is smoother and lies deeper than the southern part, which is characterized by subglacial ridges and individual mounts rising from 750 m a.s.l. to about 1100 m. A number of ridges radiate out from the caldera, however, none toward south. One ridge strikes west toward the neighbouring volcano Eyjafjallajökull, and a second ridge strikes E from the eastern rim of the caldera. Ridges also radiate from the caldera rim toward NW, N, and NE. A linear depression, bounded by steep slopes, 200-250 m deep and 1.5 km wide, strikes NE toward the volcanic fissure Eldgjá. Twenty eruptions have been documented from the caldera during the last 1100 years, all causing catastrophic jökulhlaups. Over the last four centuries eruptions have occurred on single vents and volcanic fissures trending both E-W and S-N. We suggest that the largest eruption of the last millennium (1755 A.D.) took place on a several kilometers long fissure trending east from Goðabunga; and the eruptions of 1823 and 1918 on a northerly striking ridge from the eastern rim of Háabunga. At present, meltwater drains southeastward, down to Mýrdalssandur, from an area of 60 km within the caldera. All but two of the 20 recorded jökulhlaups in historical times have taken this path. An area of about 20 km within the caldera drains to the southwest, down to Sólheimasandur. Two jökulhlaups are known to have taken this route to the river Jökulsá á Sólheimasandi in historical times. A third route, northwestward into Fremri Emstruá and the Markarfljót river, was taken by a prehistoric jökulhlaup in 1600 B.P. Presently, geothermal activity is displayed by several small cauldrons, 0.5-1 km in diameter on the glacier surface. Meltwater accumulates beneath two or three of these cauldrons and is frequently drained in small jökulhlaups.