Debris flow initiation from ravel-filled channel bed failure following wildfire in a bedrock landscape with limited sediment supply
Debris flow initiation from ravel-filled channel bed failure following wildfire in a bedrock landscape with limited sediment supply
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在沉积物供应有限的基岩景观中，野火后布满散乱的河床破坏引发泥石流
DOI：
10.1130/b35822.1
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
M. Lamb
中科院分区：
文献类型：
--
作者：
M. Palucis;T. Ulizio;M. Lamb
陡峭的岩石景观通常会在野火后产生大量沉积物和泥石流。泥石流可以由土壤覆盖部分的山体滑坡或细流引发，但很少有直接观察到泥石流在缺乏厚的、连续的土壤覆盖层的陡峭、岩石部分中引发。我们监测了美国加利福尼亚州圣盖博山脉燃烧的一个陡峭的一级流域。火灾发生后、降雨之前，大部分山坡土幔被干散布去除，露出基岩，并在河道网络中沉积约 0.5 m 的沙质沉积物。在一年一遇的暴雨中，泥石流在河道网络中引发，疏散了累积的干燥碎石和下面的卵石床，并将河道冲刷至基岩。该河道紧邻一个犁过的阶地，可以提供完整的沉积物预算，证实泥石流扇中沉积的沉积物约 95% 与从河道中疏散的沉积物相匹配，降雨驱动的山坡贡献较小。随后的较大风暴在高阶河道中产生了泥石流，但由于沉积物供应的限制，在一级河道中没有产生泥石流。这些观察结果与陡峭岩石景观中火灾后散布路径的模型一致，其中沉积物来自于植被坝的焚烧（自上次火灾以来约 30 年的山坡土壤生产），并通过干燥过程向下坡输送，导致山坡沉积物供应有限，并用相对细的沉积物填充低阶河道。我们对泥石流引发的观察结果与河道床冲积层的破坏一致，这是由于干燥的拉威尔沉积物导致颗粒尺寸减小，即使在中等强度的暴雨中，也允许高盾牌数和质量破坏。
Steep, rocky landscapes often produce large sediment yields and debris flows following wildfire. Debris flows can initiate from landsliding or rilling in soil-mantled portions of the landscape, but there have been few direct observations of debris flow initiation in steep, rocky portions of the landscape that lack a thick, continuous soil mantle. We monitored a steep, first-order catchment that burned in the San Gabriel Mountains, California, USA. Following fire, but prior to rainfall, much of the hillslope soil mantle was removed by dry ravel, exposing bedrock and depositing ∼0.5 m of sandy sediment in the channel network. During a one-year recurrence rainstorm, debris flows initiated in the channel network, evacuating the accumulated dry ravel and underlying cobble bed, and scouring the channel to bedrock. The channel abuts a plowed terrace, which allowed a complete sediment budget, confirming that ∼95% of sediment deposited in a debris flow fan matched that evacuated from the channel, with a minor rainfall-driven hillslope contribution. Subsequent larger storms produced debris flows in higher-order channels but not in the first-order channel because of a sediment supply limitation. These observations are consistent with a model for post-fire ravel routing in steep, rocky landscapes where sediment was sourced by incineration of vegetation dams—following ∼30 years of hillslope soil production since the last fire—and transported downslope by dry processes, leading to a hillslope sediment-supply limitation and infilling of low-order channels with relatively fine sediment. Our observations of debris flow initiation are consistent with failure of the channel bed alluvium due to grain size reduction from dry ravel deposits that allowed high Shields numbers and mass failure even for moderate intensity rainstorms.
源头水道的干燥沉积物加剧了基岩景观中野火后的泥石流
影响因子：
5.8
作者：
DiBiase, Roman A.;Lamb, Michael P.
通讯作者：
Lamb, Michael P.