In the semiarid Southwestern USA, wildfires are commonly followed by runoff-generated debris flows because wildfires remove vegetation and ground cover, which reduces soil infiltration capacity and increases soil erodibility. At a study site in Southern California, we initially observed runoff-generated debris flows in the first year following fire. However, at the same site three years after the fire, the mass-wasting response to a long-duration rainstorm with high rainfall intensity peaks was shallow landsliding rather than runoff-generated debris flows. Moreover, the same storm caused landslides on unburned hillslopes as well as on slopes burned 5 years prior to the storm and areas burned by successive wildfires, 10 years and 3 years before the rainstorm. The landslide density was the highest on the hillslopes that had burned 3 years beforehand, and the hillslopes burned 5 years prior to the storm had low landslide densities, similar to unburned areas. We also found that reburning (i.e., two wildfires within the past 10 years) had little influence on landslide density. Our results indicate that landscape susceptibility to shallow landslides might return to that of unburned conditions after as little as 5 years of vegetation recovery. Moreover, most of the landslide activity was on steep, equatorial-facing slopes that receive higher solar radiation and had slower rates of vegetation regrowth, which further implicates vegetation as a controlling factor on post-fire landslide susceptibility. Finally, the total volume of sediment mobilized by the year 3 landslides was much smaller than the year 1 runoff-generated debris flows, and the landslides were orders of magnitude less mobile than the runoff-generated debris flows.

中文翻译：

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野火后的山体滑坡：发生、规模和流动性

在半干旱的美国西南部，野火通常伴随着径流产生的泥石流，因为野火移除了植被和地面覆盖物，从而降低了土壤渗透能力并增加了土壤可蚀性。在南加州的一个研究地点，我们最初观察到火灾发生后第一年径流产生的泥石流。然而，在火灾三年后的同一地点，对具有高降雨强度峰值的长期暴雨的大规模浪费反应是浅层滑坡，而不是径流产生的泥石流。此外，同一场风暴在未燃烧的山坡以及在风暴前 5 年被烧毁的山坡上以及在暴雨前 10 年和 3 年被连续野火烧毁的地区造成山体滑坡。山体滑坡密度在 3 年前烧毁的山坡上最高，风暴前 5 年被烧毁的山坡滑坡密度低，与未烧毁的地区相似。我们还发现重新燃烧（即过去 10 年内发生的两次野火）对滑坡密度几乎没有影响。我们的结果表明，景观对浅层滑坡的敏感性可能会在植被恢复短短 5 年后恢复到未燃烧的条件。此外，大部分滑坡活动发生在陡峭的、面向赤道的斜坡上，这些斜坡接收到较高的太阳辐射，植被再生速度较慢，这进一步表明植被是火灾后滑坡敏感性的控制因素。最后，第 3 年滑坡动员的泥沙总量远小于第 1 年径流产生的泥石流，