Fire, storms, and erosional events in the Idaho batholith
Fire, storms, and erosional events in the Idaho batholith
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DOI：
10.1002/hyp.389
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发表时间：
2001-10
影响因子：
3.2
通讯作者：
G. Meyer;J. Pierce;S. Wood;A. Jull
中科院分区：
文献类型：
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作者：
G. Meyer;J. Pierce;S. Wood;A. Jull
1996年12月下旬，爱达荷州中西部的南福克帕耶特河流域经历了一场长时间的风暴，并于1997年1月1日达到高潮，积雪融化带来的暴雨引发了滑坡，产生了泥石流和泥沙泛滥。失败发生在饱和的、无黏结的、长满草的崩积层中，这些崩积层来自风化的爱达荷岩基花岗质岩石。南福克帕耶特河沿岸的许多失败都源于1989年洛曼林场大火中烧毁的黄松林。一个例子是0.49平方公里的“Jughead”溪盆地，在那里，一次大的崩塌破坏产生了盆地侵蚀总量的近40%，并产生了大规模和快速的泥石流。失败也发生在陡峭的、未燃烧的和未森林的流域，如霍普金斯河。在这个向南0.58 km2的盆地中，有15个崩塌空洞破坏，但没有一个破坏产生超过总侵蚀体积的10%。霍普金斯河的泥沙运输是由长时间的含沙薄片洪水引起的。尽管植被不同，地貌相似的Hopkins Creek （~ 42000 Mg km−2）和Jughead Creek （~ 44000 Mg km−2）盆地的产沙量非常相似。这些1997年的侵蚀事件相当于几千年的低产沙率（2.7 - 30 Mg km2年−1），通过短期沉积物捕获和测量在爱达荷州基底流域测量得到。如果类似的大事件是沉积物输出的唯一原因，那么几百年的复发间隔（RIs）将解释爱达荷州基底流域平均超过104年的较高沉积物产出量。Jughead Creek全新世早期支流交汇处扇的小型火淹事件测年表明，在7400 ~ 6600 cal year BP之间发生了频繁的小型沉积事件（RI≈33 ~ 80年），平均产量不超过16 Mg km−2 year−1。与全新世平均值相比，这800年期间的侵蚀速率异常低，这表明沉积物产量在一段时间内并不是恒定的，气候变化和相关的火灾制度变化可能对主要侵蚀事件的概率产生强烈影响。版权所有©2001约翰威利父子有限公司
In late December 1996, the South Fork Payette River basin in west‐central Idaho experienced a prolonged storm that culminated on January 1, 1997, with intense rain on melting snow that triggered slide failures, producing debris flows and sediment‐charged floods. Failures occurred in saturated, cohesionless, grussy colluvium derived from weathered Idaho batholith granitic rocks. Many failures along the South Fork Payette River originated in ponderosa pine forests burned in the 1989 stand‐replacing Lowman fire. An example is the 0·49 km2 ‘Jughead’ Creek basin, where a single large colluvial failure produced almost 40% of the total volume eroded from the basin and generated a massive and rapid debris flow. Failures also occurred in steep, unburned, and unforested drainages such as Hopkins Creek. In this south‐facing 0·58 km2 basin, 15 colluvial hollows failed, but no single failure produced more than 10% of the total eroded volume. Sediment transport in Hopkins Creek occurred by prolonged sediment‐charged sheetflooding. Despite vegetation differences, sediment yields from the geomorphically similar Hopkins Creek (∼42 000 Mg km−2) and Jughead Creek (∼44 000 Mg km−2) basins were quite similar. These 1997 erosion events are equivalent to several thousand years of sediment yield at low rates (2·7–30 Mg km2 year−1) measured by short‐term sediment trapping and gauging in Idaho batholith watersheds. If similar large events were solely responsible for sediment export, recurrence intervals (RIs) of several hundred years would account for higher sediment yields averaged over ∼104 year from Idaho batholith watersheds. Dating of small fire‐induced sheetflooding events in an early Holocene tributary junction fan of Jughead Creek indicates that frequent small sedimentation events (RI≈33–80 year) occurred between 7400 and 6600 cal year BP, with an average yield not greatly exceeding 16 Mg km−2 year−1. Compared with the Holocene average, erosion rates during that 800 year period were unusually low, suggesting that sediment yields have not been constant over time, and that climatic variations and related fire regime changes may exert a strong influence on the probability of major erosional events. Copyright © 2001 John Wiley & Sons, Ltd.