J.J. Roering Francis K. Rengers Sara Wall 2020 <p><span>Wildfires dramatically alter the hydraulics and root reinforcement of soil on forested hillslopes, which can promote the generation of debris flows. In the Pacific Northwest, post-fire shallow landsliding has been well documented and studied, but the potential role of runoff-initiated debris flows is not well understood and only one previous to 2018 had been documented in the region. On 20 June 2018, approximately 1&nbsp;year after the Milli fire burned 24,000 acres, a runoff-initiated debris flow occurred on the flanks of Black Crater in the Oregon Cascade Range. The debris flow was initiated via dispersed rilling on &gt; 30-degree slopes near the crater rim and traveled &gt; 1.5&nbsp;km downslope. We measured exceptionally low soil infiltration rates at the study site, likely due to high burn severity during the Milli fire. Based on nearby 5-min rain gage data, we quantified rainfall rates for the storm event that triggered the debris flow. Our results show that peak 15-min rainfall rates were 25.4&nbsp;mmh</span>⁻¹<span>, equaling or exceeding the measured infiltration rates at the study site, which had a geometric mean of ~ 24&nbsp;mmh</span>⁻¹<span>. Field mapping shows that high burn severity resulted in the initiation of the debris flow and that convergent and steep topography promoted the development of a debris flow at this site. As wildfires increase in frequency and intensity across the western USA, the Pacific Northwest could become more susceptible to runoff-initiated debris flows. Therefore, characterization of the conditions that resulted in this debris flow is crucial for understanding how runoff-initiated debris flows may shape terrain and impact hazards in the Pacific Northwest.</span></p> application/pdf 10.1007/s10346-020-01376-9 en Springerlink Runoff-initiated post-fire debris flow Western Cascades, Oregon article