Sedimentary and Geomorphic Responses to Ignimbrite Emplacement: Readjustment of the Waikato River after the a.d. 181 Taupo Eruption, New Zealand
Sedimentary and Geomorphic Responses to Ignimbrite Emplacement: Readjustment of the Waikato River after the a.d. 181 Taupo Eruption, New Zealand
复制标题
对火晶岩侵位的沉积和地貌响应：公元后怀卡托河的重新调整
DOI：
10.1086/341596
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
V. Manville
中科院分区：
文献类型：
--
作者：
V. Manville
大规模爆发性火山爆发后地貌的重新调整是物理沉积学和地貌学中最引人注目的过程之一。流纹岩火山口的大规模熔结凝灰岩侵位喷发可以形成超过104平方公里的新景观，在火山口形成新的沉积中心，并将现有的地形和排水系统埋在数百米的火山碎屑物质之下。这些碎片随后的重新流动构成了广泛和持久的危险。在新西兰北岛中部，公元181年的陶波火山爆发摧毁了超过120，000平方公里的水文系统，当时火山灰凝灰岩的侵位充满了山谷和洼地，火山碎屑物质高达70米，阻塞了怀卡托河通往内卡尔德拉湖盆地的出口。这种材料在怀卡托流域的Posteruption再动员与轴流重建。垂直，横向和近端-远端的变化，火山岩相保存沿着主要山谷反映了不断变化的沉积物运输和沉积体系的爆发后，可用于重建不断变化的水文，泥沙产量和当地亚环境之间的相互作用。在质量流占主导地位的初始阶段之后，河流系统的重建开始于通过积水熔结凝灰岩对箱形峡谷的溯源侵蚀。随着排水网络的重新整合，以及通过植被恢复和易再活化物质库的耗尽，沉积物产量下降，这些河道中的溪流从浅的、短暂的、充满泥沙的水流演变为更永久的辫状河。在ca. 20年前，陶波湖出口处的熔结凝灰岩屏障被重新填充的intracaldera湖打破，引发了怀卡托河20 km 3的洪水释放。短暂复兴的支流随后稳定的当地基准面和流量有效地终止了posteruptive景观响应期间。
The posteruption readjustment of landscapes to major explosive volcanic eruptions is one of the most dramatic processes in physical sedimentology and geomorphology. Large ignimbrite‐emplacing eruptions from rhyolitic caldera volcanoes can form new landscapes over >104 km2, create new depocenters in calderas, and bury existing topography and drainage systems beneath hundreds of meters of pyroclastic material. Subsequent remobilization of this debris constitutes a widespread and enduring hazard. In the central North Island of New Zealand, the a.d. 181 Taupo eruption destroyed hydrologic systems over ∼20,000 km2 when emplacement of the climactic ignimbrite filled valleys and depressions with up to 70 m of pyroclastic material and blocked the Waikato River outlet to the intracaldera lake basin. Posteruption remobilization of this material in the Waikato catchment was associated with axial stream reestablishment. Vertical, lateral, and proximal‐distal changes in volcaniclastic lithofacies preserved along the main valley reflect evolving sediment transport and depositional systems in the eruption aftermath and may be used to reconstruct the interplay between evolving hydrographs, sediment yields, and local subenvironments. Following an initial period dominated by mass flows, reestablishment of fluvial systems began with the headward erosion of box canyons through ponded ignimbrite. Streams in these channels evolved from shallow, ephemeral, sediment‐laden flows to more permanent braided rivers as drainage networks reintegrated and sediment yields declined through revegetation and depletion of the reservoir of easily remobilized material. After ca. 20 yr, the ignimbrite barrier at the outlet to Lake Taupo was breached by the refilling intracaldera lake, triggering the release of 20 km3 of floodwater down the Waikato River. Brief rejuvenation of tributaries followed before stabilization of local base levels and flows effectively terminated the period of posteruptive landscape response.