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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Linking the Ukinrek 1977 maar-eruption observations to the tephra deposits: New insights into maar depositional processes
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Linking the Ukinrek 1977 maar-eruption observations to the tephra deposits: New insights into maar depositional processes

机译：将Ukinrek 1977年的玛拉火山喷发观测与特非拉沉积物联系起来：对玛阿尔沉积过程的新见解

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The Ukinrek Maars erupted 30 March to 9 April 1977, forming two maars, a line of small pit craters and a tephra blanket extending to similar to 2 km from the vents. We combine photographic and written observations with strati graphic analysis to reconstruct the eruption. The eruption began with very low (a few meters high) fountaining from small craters above an inferred east-west-trending dike, creating local scoria/spatter agglomerate ramparts with a sandy matrix. The eruption very quickly (in minutes to hours) centered on the West Maar. The West Maar eruption lasted 1-2 days, starting and ending with phreatomagmatic explosions with weak phreato-Strombolian activity in between. Initial explosions formed a 30-m-wide crater, enlarged by crater-wall collapse, and columns as high as 6500 m. Phreato-Strombolian activity produced similar to 72% of the erupted volume, including a small spatter cone and a scoria blanket around the vent. A final explosion series emplaced a lithic-rich breccia as ballistic blocks, possibly as the northern half of the final crater collapsed into the southern vent area. The East Maar formed over the last nine days of the eruption and represents similar to 93% of the total volume (4.6 x 10(6) m(3)) of the Ukinrek eruption. Initial explosions were probably shallower than 10-20 m but most of the eruption occurred from explosions at 50-60 m below the pre-eruptive surface, with evidence of explosions to 90 m depth only at the very end of the eruption. The East Maar eruption mostly produced columns of lapilli, ash, and steam and the deposits are mostly fallout. Winds blew fallout mostly to the north for the first 5-6 days and to the south for the last three days of the eruption. Wind-directed pyroclastic density currents collapsed from the column, producing fines-rich layers within the coarser fallout. Sporadic explosions produced weak density currents in the first few days and lithic-and juvenile-block-rich breccias in the last few days of the eruption. We interpret that collapse of the crater walls made a slurry that in part provided the water for phreatomagmatic interaction. Explosions came from depths 90 m below the pre-eruptive surface except for a few explosions at the end of the eruption, with most occurring at 70 m depth. The East Maar crater was open to 40-60 m depth throughout most of the eruption, so the explosions were rarely, if ever, deeper than 30 m below the crater floor. Thus, we infer there is no classic, well-formed diatreme structure below the maar. Collapse of the East Maar crater walls provided a supply of water-saturated sediment for much of the phreatomagmatic activity, which came from two vents that did not migrate much, if at all, during the eruption. The Ukinrek Maars deposits were nearly entirely emplaced by fallout, rather than density currents, from explosions and low columns. (C) 2018 Elsevier B.V. All rights reserved.
机译：Ukinrek Maars爆发于1977年3月30日至4月9日，形成了两个Maars，一排小坑坑和一个延伸到距喷口约2公里的提夫拉毯。我们将摄影和书面观察与地层图形分析相结合，以重建喷发。火山喷发始于从一个推测的东西向趋势堤防上方的小火山口喷出的非常低（几米高）的喷泉，形成了带有砂质基质的局部火山灰/飞溅的聚结城墙。喷发非常迅速（几分钟到几小时）就集中在西玛尔。西马尔火山喷发持续了1-2天，开始和结束时是岩浆爆发，其间的岩浆-Strombolian活动较弱。最初的爆炸形成了一个30米宽的陨石坑，并由于陨石坑壁的坍塌而扩大，圆柱高达6500 m。 Phreato-Strombolian活动产生的喷发量约占喷发量的72％，包括小喷溅锥和喷口周围​​的熔渣毯。最终的爆炸系列将富含石块的角砾岩设置为弹道，可能是因为最后的火山口的北半部塌陷到南部的发泄区域。东Maar在喷发的最后九天形成，约占Ukinrek喷发总体积（4.6 x 10（6）m（3））的93％。最初的爆炸可能比10-20 m浅，但大多数喷发是由喷发前表面以下50-60 m处的爆炸产生的，只有在喷发的最后才有爆炸到90 m深度的证据。 East Maar火山喷发主要产生了lapilli，灰烬和蒸汽柱，且沉积物大部分为沉淀物。在爆发的前5-6天，大风向北吹，最后三天向南吹。风导的火山碎屑密度流从柱子上坍塌，在较粗大的沉降物中产生了富含细粉的层。零星的爆炸在爆发的最初几天产生弱的密度流，并在爆发的最后几天产生富含石块和幼虫的角砾岩。我们解释说，火山口壁的坍塌会形成泥浆，从而部分为水与岩浆相互作用提供水。爆炸来自喷发前地表以下<90 m的深度，但喷发结束时发生了几次爆炸，大多数爆炸发生在<70 m的深度。在整个喷发过程中，东马尔火山口的深度一直在40-60 m，因此爆炸很少，甚至从来没有超过火山口底部30 m以下。因此，我们推断在马阿尔下方没有经典的，结构良好的diatreme结构。 East Maar火山口壁的坍塌为大部分岩浆活动提供了水饱和的沉积物，这些沉积物来自两个喷口，在喷发过程中这些喷口并没有迁移。 Ukinrek Maars矿床几乎完全被爆炸和低柱的沉降物而非密度流所包围。 （C）2018 Elsevier B.V.保留所有权利。

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