The role of infrequently mobile boulders in modulating landscape evolution and geomorphic hazards
The role of infrequently mobile boulders in modulating landscape evolution and geomorphic hazards
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不频繁移动的巨石在调节景观演化和地貌灾害中的作用
DOI：
10.1016/j.earscirev.2021.103717
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发表时间：
2021
影响因子：
12.1
通讯作者：
Shobe C
中科院分区：
文献类型：
--
作者：
Shobe C
景观沉积物粒度分布是地表过程和景观演化的产物，并对地表过程和景观演化产生重要影响。颗粒可以足够大，以至于单个颗粒的运动，在大小选择性运输系统中很少移动的，构成或触发重大的地貌变化。我们将这些颗粒定义为巨砾。巨石影响景观演变，其动态和景观形式的影响一直是最近大量社区努力的重点。我们回顾了五个关键问题的进展有关的巨石如何影响的演变未冰川，侵蚀景观：1）什么因素控制巨石生产侵蚀山坡和随后的下坡演变的巨石尺寸分布？2)巨石如何影响山坡过程和长期山坡演变？3)漂砾如何影响河流作用和河道形状？4)巨石覆盖的渠道和山坡如何相互作用，以确定巨石影响的景观的长期形式和演变？5)巨石是如何造成地貌灾害的，以及如何利用对巨石动力学的更好理解来减轻地质灾害？在侵蚀的山坡上，由于滑坡、落石和/或通过临界区的折返作用，产生了巨石。在当地的泥沙输运为主的山坡上，卵石影响山坡土壤生产和运输过程，使下坡卵石的大小分布设置的形式稳定状态的山坡。非本地泥沙运输为主的山坡不太可能表现出巨石控制山坡形态的巨石被迅速运送到山坡趾。顺坡输运将漂砾输送到侵蚀河流，漂砾充当改变水流水力学和侵蚀及泥沙输运效率的大粗糙度元素。在较长的时间尺度上，河道调整其几何形状，以适应来自邻近山坡的巨石，使河流可以侵蚀基准面下降率给定的巨石尺寸分布。运送巨石从山坡到渠道，与渠道响应巨石交付，驱动器通道山坡反馈，影响瞬态演变和稳态形式的巨石影响的景观。在事件的规模，巨石动态侵蚀景观的一个组成部分，可以减轻与巨石生产和流动性相关的速率和过程的理解。未来工作的机会主要需要在景观边界条件（构造，气候和岩性）的梯度，以了解巨石动态景观自组织的一个组成部分的目标，以现场为重点的数据收集。
A landscape’s sediment grain size distribution is the product of, and an important influence on, earth surface processes and landscape evolution. Grains can be large enough that the motion of a single grain, infrequently mobile in size-selective transport systems, constitutes or triggers significant geomorphic change. We define these grains as boulders. Boulders affect landscape evolution; their dynamics and effects on landscape form have been the focus of substantial recent community effort. We review progress on five key questions related to how boulders influence the evolution of unglaciated, eroding landscapes: 1) What factors control boulder production on eroding hillslopes and the subsequent downslope evolution of the boulder size distribution? 2) How do boulders influence hillslope processes and long-term hillslope evolution? 3) How do boulders influence fluvial processes and river channel shape? 4) How do boulder-mantled channels and hillslopes interact to set the long-term form and evolution of boulder-influenced landscapes? 5) How do boulders contribute to geomorphic hazards, and how might improved understanding of boulder dynamics be used for geohazard mitigation?Boulders are produced on eroding hillslopes by landsliding, rockfall, and/or exhumation through the critical zone. On hillslopes dominated by local sediment transport, boulders affect hillslope soil production and transport processes such that the downslope boulder size distribution sets the form of steady-state hillslopes. Hillslopes dominated by nonlocal sediment transport are less likely to exhibit boulder controls on hillslope morphology as boulders are rapidly transported to the hillslope toe. Downslope transport delivers boulders to eroding rivers where the boulders act as large roughness elements that change flow hydraulics and the efficiency of erosion and sediment transport. Over longer timescales, river channels adjust their geometry to accommodate the boulders supplied from adjacent hillslopes such that rivers can erode at the baselevel fall rate given their boulder size distribution. The delivery of boulders from hillslopes to channels, paired with the channel response to boulder delivery, drives channel-hillslope feedbacks that affect the transient evolution and steady-state form of boulder-influenced landscapes. At the event scale, boulder dynamics in eroding landscapes represent a component of geomorphic hazards that can be mitigated with an improved understanding of the rates and processes associated with boulder production and mobility. Opportunities for future work primarily entail field-focused data collection across gradients in landscape boundary conditions (tectonics, climate, and lithology) with the goal of understanding boulder dynamics as one component of landscape self-organization.
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