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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Formation of OEskjuvatn caldera at Askja, North Iceland: Mechanism of caldera collapse and implications for the lateral flow hypothesis
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Formation of OEskjuvatn caldera at Askja, North Iceland: Mechanism of caldera collapse and implications for the lateral flow hypothesis

机译：冰岛北部Askja OEskjuvatn破火山口的形成：破火山口塌陷的机理及其对侧向流动假设的影响

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The OEskjuvatn caldera at Askja volcano, North Iceland, was formed as a result of an explosive eruption at Askja on 28th-29th March 1875. OEskjuvatn is one of the youngest collapse calderas on Earth, and its initiation and growth were observed and documented by explorers and geologists working in the Askja region between 1875 and 1932. It is an example of caldera formation where the volume of the caldera collapse far exceeds the volume of associated erupted products. The discrepancy between the collapse volume and associated erupted products has been used by previous workers as a justification for the hypothesis that the injection of lateral dykes from Askja fed the February to October 1875 Nyjahraun fissure eruptions at the Sveinagja graben, some 60 km north of Askja. However, historical accounts documenting the caldera formation in sufficient detail show clearly that OEskjuvatn formed by piecemeal collapse, taking over 40 years to reach its current form. We use these accounts to undertake a detailed examination of the stages of caldera collapse and to compare them with the known magmatic output of Askja in the years following the 1875 eruption. ArcGIS software was used to calculate the volume of OEEskjuvatn during the various stages of collapse, and the volume of material erupted after 1875. While a dyke extending between Askja and Sveinagja may be implied to account for the 'missing' volume, our results demonstrate that the volume of OEskjuvatn in July 1875 closely corresponds to the volume of rhyolitic material erupted on 28th-29th March 1875. In addition, geochemical evidence indicates that the Nyjahraun magmas were sourced from a deeper reservoir rather than by lateral injection from Askja's shallow crustal magma chamber. We therefore suggest that the injection of sills and dykes in a coherent intrusion complex beneath Askja central volcano, combined with background deflation of the magma storage zone beneath OEskjuvatn caldera over 30 to 40 years following 1875, satisfactorily accommodates the volume required to form OEskjuvatn caldera.
机译：北部冰岛阿斯克亚火山的OEskjuvatn破火山口是1875年3月28日至29日在阿斯克亚的一次喷发爆炸形成的。OEskjuvatn是地球上最年轻的坍塌破火山口之一，探险家观察到了这种破火山口并对其进行了记录以及在1875年至1932年之间在Askja地区工作的地质学家。这是破火山口形成的一个例子，破火山口塌陷的体积远远超过了相关喷发产品的体积。以前的工作人员已经使用了坍塌体积与相关喷发产品之间的差异作为以下假设的依据：Askja的侧向堤坝注入是1875年2月至10月10日Nyjahraun裂隙喷发在Askjagja en陷处（距Askja以北约60公里） 。然而，足够详细地记录破火山口形成的历史记录清楚地表明，由零散的塌陷形成的OEskjuvatn花费了40多年的时间才能达到其当前形态。我们使用这些资料对破火山口塌陷的阶段进行详细检查，并将其与1875年喷发后的几年里Askja已知的岩浆产出进行比较。使用ArcGIS软件计算了坍塌各个阶段的OEEskjuvatn体积，以及1875年后喷发的材料体积。虽然可能暗示在Askja和Sveinagja之间延伸的堤坝是“遗漏”体积的原因，但我们的结果表明1875年7月的OEskjuvatn量与1875年3月28日至29日喷发的流纹岩物质的量非常接近。此外，地球化学证据表明，Nyjahraun岩浆来自更深的储层，而不是通过Askja浅地壳岩浆室的侧向注入。因此，我们建议在1875年后的30至40年内，在Askja中央火山下方一个连贯的侵入复合物中注入基石和堤坝，并结合OEskjuvatn破火山口下方岩浆储存区的背景放气，可以令人满意地容纳形成OEskjuvatn破火山口的体积。

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