Multi-decadal changes in the relationships between rainfall characteristics and debris-flow occurrences in response to gully evolution after the 1990-1995 Mount Unzen eruptions
Multi-decadal changes in the relationships between rainfall characteristics and debris-flow occurrences in response to gully evolution after the 1990-1995 Mount Unzen eruptions
复制标题
1990-1995年云仙火山喷发后沟壑演化对降雨特征与泥石流发生关系的数十年变化
DOI：
10.1002/esp.5148
复制
发表时间：
2021
影响因子：
3.3
通讯作者：
Sakai Y
中科院分区：
文献类型：
--
作者：
Tsunetaka H;Shinohara Y;Hotta N;Gomez C;Sakai Y
火山爆发会引起长期的景观变化，导致沉积物排放增加，这种变化在火山喷发停止后仍在继续。1990年至1995年期间，日本云禅山喷发产生了大量火山碎屑物质，导致1991年至2018年期间发生了57次泥石流事件。为了研究降雨特征与泥石流发生之间的关系变化，我们进行了以下工作：利用激光雷达（光探测和测距）生成的1 m dem（数字高程模型）对两个沟壑（即泥石流起爆区）进行几何分析；降雨分析，基于降雨持续时间与平均强度的关系（即考虑强度-持续时间、orID、阈值）；2016-2018年泥石流监测。自1991年以来，降雨径流对供应的火山碎屑物质造成侵蚀，形成了由切割的沟壑组成的河道网络。降雨充足时，泥石流形成，沟壑进一步侵蚀；这导致垂直和横向调整的横截面几何形状。在火山喷发停止后的二十年里，由于沟壑已经适应了当地的水文条件，容易动员的火山碎屑物质已经变得稀缺。同时，火山翼的入渗能力增加，减少了坡面流的能力。因此，自2000年以来，出现了强度超过阈值的降雨事件；然而，由于沟槽沉积物的缺乏，阻碍了泥石流的发生和发展。这表明，火山扰动景观中的泥石流可能发生在较低的降雨阈值，只要相应的高地河道由于强烈的陆面流而演变。然而，随着这些河道向平衡几何形状演变，泥石流的频率随着可利用泥沙的减少而减少。
Explosive volcanic eruptions can cause long‐term landscape change, leading to increased sediment discharge that continues after the cessation of the eruptions. During the period 1990–1995, eruptions of Mount Unzen, Japan, generated large amounts of pyroclastic material, resulting in 57 debris‐flow events during 1991–2018. To investigate changes in the relationships between rainfall characteristics and debris‐flow occurrence, we conducted the following: geometric analysis of two gullies (i.e., debris‐flow initiation zones) using LiDAR (light detection and ranging)‐generated 1 m DEMs (digital elevation models); rainfall analysis, based on the relationship between rainfall duration and mean intensity (i.e., considering the intensity–duration, orID, threshold); and debris‐flow monitoring during 2016–2018. Since 1991, rainfall runoff has caused erosion of the supplied pyroclastic material, generating a channel network consisting of incised gullies. With sufficient rainfall, debris flows formed, accompanied by further gully erosion; this resulted in both vertical and lateral adjustments of the cross‐sectional geometry. In the two decades since the eruptions ceased, readily mobilized pyroclastic material has become scarce as the gullies have adjusted to local hydrographic conditions. At the same time, the infiltration capacity of the volcanic flank has increased, reducing the capacity for overland flow. As a result, since 2000, rainfall events with intensities above theIDthreshold have occurred; however, the lack of sediment supplied by the gullies appears to have hindered the occurrence and development of debris flows. This suggests that debris flows in volcanically perturbed landscapes may occur at lower rainfall thresholds as long as the corresponding upland channels are evolving as a result of intense overland flow. However, as such channels evolve towards equilibrium geometries, the frequency of debris flows decreases in response to the reduction in sediment availability.