Quantitative reconstruction of late Holocene surface evolution on an alpine debris-flow fan
Quantitative reconstruction of late Holocene surface evolution on an alpine debris-flow fan
复制标题
DOI：
10.1016/j.geomorph.2016.09.020
复制
发表时间：
2016-12
期刊：
影响因子：
3.9
通讯作者：
P. Schuerch;A. Densmore;S. Ivy‐Ochs;N. Rosser;F. Kober;F. Schlunegger;B. McArdell;V. Alfimov
中科院分区：
文献类型：
--
作者：
P. Schuerch;A. Densmore;S. Ivy‐Ochs;N. Rosser;F. Kober;F. Schlunegger;B. McArdell;V. Alfimov
泥石流扇形成了山区过去泥石流活动的普遍记录，并可能有助于推断过去的流动特征和随之而来的未来灾害。然而，从扇记录中提取过去泥石流的信息，需要了解泥石流沉积和扇面演变;对这些过程的实地研究非常有限。在本文中，我们记录的模式和时间的碎屑流沉积在表面上的大型和异常活跃的伊尔格拉本风扇在瑞士西南部。我们使用地形分析，放射性碳测年的沉积物填充在伊尔格拉本流域，和cosmogenic 10 Be和36 Cl暴露测年的碎屑流沉积物上的风扇，以限制在过去的3200年的时间演变的沉积物路由系统的流域和风扇。我们表明，扇面保留了一组碎屑流瓣，这些碎屑流瓣主要是在大约3200年前扇尖附近发生大型岩石雪崩后沉积的。这次岩石雪崩移动了扇形的顶点，并将沉积物滞留在伊尔格拉本集水区。随后的演变的扇面一直受到横向和径向的变化，在活跃的沉积叶，揭示了宇宙成因的放射性核素日期和横切几何关系的扇面。这种模式的频繁撕脱和风扇表面占领提供了现场规模的证据，在实验沉积物路由系统中观察到的大规模补偿行为的类型。
Debris-flow fans form a ubiquitous record of past debris-flow activity in mountainous areas, and may be useful for inferring past flow characteristics and consequent future hazard. Extracting information on past debris flows from fan records, however, requires an understanding of debris-flow deposition and fan surface evolution; field-scale studies of these processes have been very limited. In this paper, we document the patterns and timing of debris-flow deposition on the surface of the large and exceptionally active Illgraben fan in southwestern Switzerland. We use terrain analysis, radiocarbon dating of sediment fill in the Illgraben catchment, and cosmogenic10Be and36Cl exposure dating of debris-flow deposits on the fan to constrain the temporal evolution of the sediment routing system in the catchment and on the fan during the past 3200 years. We show that the fan surface preserves a set of debris-flow lobes that were predominantly deposited after the occurrence of a large rock avalanche near the fan apex at about 3200 years ago. This rock avalanche shifted the apex of the fan and impounded sediment within the Illgraben catchment. Subsequent evolution of the fan surface has been governed by both lateral and radial shifts in the active depositional lobe, revealed by the cosmogenic radionuclide dates and by cross-cutting geometrical relationships on the fan surface. This pattern of frequent avulsion and fan surface occupation provides field-scale evidence of the type of large-scale compensatory behavior observed in experimental sediment routing systems.