Debris flows are highly unpredictable and mechanically chaotic phenomena that can spread or branch away from an expected path or pre-existing channel, a phenomenon termed avulsion. While avulsion is expected to occur over long time periods on mature debris fans, it can also occur on short time scales and outside of active portions of fans. This was the case during the 9–13 September 2013 rainstorm event that triggered over 1000 debris flows in the Colorado Front Range. This research examines the geomorphic and topographic characteristics of debris flows during this event to identify the controlling variables of avulsion during singular events. Avulsion was observed in 1/3 of the debris flows, which were classified into 5 distinct behaviors and thus hazard implications, including directional change, distributary, split, free spreading, and braided. Debris flows that avulsed were twice as long and 6 times more likely to have path obstructions than non-avulsed paths. Additionally, locations along a debris-flow path with low lateral confinement and decreasing slope angles were more prone to avulsion. The high frequency of avulsed debris flows during the 2013 rainstorm event emphasizes the importance of considering avulsion potential during debris-flow mitigation design. The common characteristics of avulsed flows highlighted here could be incorporated into future hazard modeling efforts.

中文翻译：

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2013 年 9 月美国科罗拉多前线暴雨事件期间的碎屑流行为

碎片流是高度不可预测的机械混沌现象，可以从预期路径或预先存在的通道扩散或分支，这种现象称为撕脱。虽然预计成熟的碎屑扇会在很长一段时间内发生撕脱，但它也可能发生在短时间尺度上，并且在扇的活动部分之外发生。2013 年 9 月 9 日至 13 日的暴雨事件就是这种情况，该事件在科罗拉多前沿山脉引发了 1000 多次泥石流。本研究检查了此次事件期间泥石流的地貌和地形特征，以确定在单一事件期间发生撕脱的控制变量。在 1/3 的泥石流中观察到撕脱，将其分为 5 种不同的行为和危害含义，包括方向改变、分流、分裂、自由扩散和编织。撕开的碎片流比未撕开的路径长两倍，路径阻塞的可能性高出 6 倍。此外，沿泥石流路径具有低侧向限制和减小倾斜角的位置更容易发生撕脱。2013 年暴雨事件期间发生的高频率撕脱泥石流强调了在泥石流减缓设计过程中考虑撕脱可能性的重要性。这里强调的破坏流的共同特征可以纳入未来的灾害建模工作。2013 年暴雨事件期间发生的高频率撕脱泥石流强调了在泥石流减缓设计过程中考虑撕脱可能性的重要性。这里强调的破坏流的共同特征可以纳入未来的灾害建模工作。2013 年暴雨事件期间发生的高频率撕脱泥石流强调了在泥石流减缓设计过程中考虑撕脱可能性的重要性。这里强调的破坏流的共同特征可以纳入未来的灾害建模工作。