Entrance of hot pyroclastic flows into the sea: experimental observations
Entrance of hot pyroclastic flows into the sea: experimental observations
复制标题
热火山碎屑流进入海洋：实验观察
作者：
A. Freundt
摘要：在一系列实验中观察到热火山碎屑流进入水中，在这些实验中，热熔结凝灰岩灰（≤ 403 ° C）的喷射颗粒流（体积密度接近水）沿着光滑的斜槽流下，并以26 °角进入充满水的槽。相对较冷的火山灰流（<150 ° C）在撞击时冲动地置换了一定体积的靠近海岸的水，产生了迅速远离海岸的水波。然后，粒状流动材料分离成两部分。(1)细灰潮云形成的地方，颗粒流击中水，并迅速向下移动罐在水面上。(2)物质的主要部分穿透表面并与水混合，形成类似于水跃的湍流混合区，只要火山碎屑流保持不变，该混合区就会向下游推进。大多数浮石浮到表面，岩屑和粗灰掉到地板上，但仍处于悬浮状态的灰形成浊流，沿着水槽的地板向下流动。随着灰温的升高，进入的材料中有越来越多的部分最初沿水表面沿着输送;几乎所有材料在温度> 250 ° C时都沿这条路径输送。在离海岸一定距离的水面上混合产生蒸汽爆炸，形成湿灰和干灰喷泉，并对流上升细灰羽流。蒸汽爆炸的强度和横向范围增加对更高的灰温度和质量通量。爆炸产生的水波仍然是由大量的喷泉落尘驱动的，从海岸经过一段距离。火山灰喷泉注入火山碎屑，这些火山碎屑在水面上以高速向下推进。从火山灰喷泉和涌浪中落下的水下沉积物羽流将粗颗粒的负荷落在地板上，而较细的负荷则形成浊流。火山碎屑流的高温和粒度分选不良是决定其与水相互作用过程和相关危害的关键参数。分选不好会形成在水面上移动的火山灰云，即使是来自冷流。高温会引起沿岸的爆炸，并促进大量物质在水上的运输。所有的流动都通过不同的机制产生海啸波。电子补充材料（两部电影）可在www.example.com上访问本文。在该页面（左侧的框架）上，有一个链接可以直接将您带到补充材料。
Abstract.The entrance of hot pyroclastic flows into water has been observed in a series of experiments in which shooting granular flows of hot ignimbrite ash (≤403 °C), of bulk density near that of water, run down a smooth chute and enter a water-filled tank at an angle of 26°. Flows of relatively cool ash (<150 °C) impulsively displace some volume of near-shore water upon impact, generating a water wave that rapidly travels away from shore. The granular flow material then separates into two portions. (1) A fine-ash surge cloud is formed where the granular flow hits water and rapidly travels down-tank over the water. (2) The main portion of material penetrates the surface and mixes with the water, creating a turbulent mixing zone resembling a hydraulic jump, which advances downstream as long as the pyroclastic flow is maintained. Most pumice floats to the surface, lithics and coarse ash fall out onto the floor, but ash that remains in suspension forms a turbidity current that travels down the floor of the tank. With increasing ash temperature, an increasing fraction of incoming material is initially transported along the water surface; almost all material takes this path at temperatures >250 °C. Mixing across the water surface over some distance from shore generates steam explosions forming fountains of wet and dry ash and convectively rising fine-ash plumes. Steam explosions increase in strength and lateral extent towards higher ash temperatures and mass fluxes. The explosions generate water waves that remain driven by massive fountain fallout across some distance from shore. The ash fountains feed pyroclastic surges, which advance down tank over water at high speeds. Underwater plumes of sediment falling from the ash fountains and surges drop coarse load onto the floor whereas the finer load forms a turbidity current. High temperature and poor size sorting of pyroclastic flows are key parameters that determine the processes of interaction with water and the associated hazards. Poor sorting allows for the formation of ash-cloud surges moving over water, even from cool flows. High temperatures cause littoral explosions and facilitate extensive mass transport over water. All flows generate tsunami waves by different mechanisms. Electronic supplementary material (two movies) is available if you access this article at http://dx.doi.org/10.1007/s00445-002-0250-1. On that page (frame on the left side), a link takes you directly to the supplementary material.