Seepage Erosion in the Luquillo Mountains, Puerto Rico, Relict Landscapes
Seepage Erosion in the Luquillo Mountains, Puerto Rico, Relict Landscapes
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DOI：
10.1029/2019jf005341
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发表时间：
2020-06-01
影响因子：
3.9
通讯作者：
Willenbring, J. K.
中科院分区：
文献类型：
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作者：
Harrison, E. J.;Brocard, G. Y.;Willenbring, J. K.
对新兴地下水对地貌形成的初步研究表明，控制河道形状和下切率的关系与其他河流系统不同（霍华德，1995年;邓恩，1980年，1990年）。虽然最近的一些工作已经将这些模型与自然环境联系起来（Abrams等人，2009; Petroff等人，2011年），其他研究表明，渗透侵蚀可能被错误地调用在景观形成的洪水和漫流（兰姆等人，2006年，2007年）。我们调查的渗透侵蚀的热带山区流域，里奥布兰科的卢基略山脉的北方波多黎各的地貌的影响。我们关注的是一群圆形剧场形的河道，这些河道切入流域高地河段的风化腐岩剖面，在那里，河流与区域基准面降低断开（Brocard等人，2015年，2016年）。尽管这些集水区的排水面积很小，但我们测量了来自这些集水区的泉水的高基流率。我们构建了一个将基流流量与流域内集水面积联系起来的经验模型。我们量化了沉积物中10 Be的长期（103-104年）流域侵蚀，并测量了基流处推移质输运的短期体积通量。在这组渠道的运输和侵蚀率的比例线性的进料流域面积和基流流量。这一发现支持了地下水驱动渠道的河流切割模型（霍华德，1995年）。我们建议，加深腐岩和一致的壕沟的地下水路由系统开始渗透侵蚀，并积极扩大在里奥布兰科的源头。简单的语言摘要地貌和形成它们在地球上的过程之间的关系，可以用来确定在工作中的过程，只能远程研究的地方，如深海或其他行星的表面。在20世纪80年代初，研究人员认识到，河道有不同的形状，这取决于它们是由地表流动的水还是地下流动的水雕刻的。早期在沙盒模型中对地下水侵蚀的研究发现，侵蚀与地下水流入河道的速率之间存在着一种独特的关系，这种关系在其他情况下是不存在的。然而，这种关系还有待于在自然景观中得到验证。在这项研究中，我们测量了形状属性，地下水流，侵蚀率在短期（小时）和长期（数万年）的时间尺度在陡峭的，山区河流的源头渠道在波多黎各的热带雨林。我们确定了一个独特的人口流的几何特性和流流量侵蚀率的关系，匹配预测的通道，由地下水流动的短期和长期的时间尺度。这是第一项研究调查地下水驱动的侵蚀使用Be-10作为一个直接的地球化学示踪剂。关键点渠道的形态模拟理论预期的地下水驱动的侵蚀从泉水基流排放可以运输河流推移质长期侵蚀率比例线性基流排放率
Seminal research into geomorphic shaping of landscapes by emerging groundwater suggest that the relationships governing channel form and incision rate are distinct from other fluvial systems (Howard, 1995; Dunne, 1980, 1990). While some recent work has connected these models to natural settings (Abrams et al., 2009; Petroff et al., 2011), other studies have shown that seepage erosion may be erroneously invoked in landscapes shaped by flooding and overland flow (Lamb et al., 2006, 2007). We investigate the impact of seepage erosion on the geomorphology of a tropical mountain watershed, the Rio Blanco in the Luquillo Mountains of northern Puerto Rico. We focus on a population of amphitheater-shaped channels that incise into deeply weathered saprolite profiles in the upland reaches of the watershed, where the river is disconnected from regional base-level lowering (Brocard et al., 2015, 2016). We measured high rates of baseflow from springs feeding these catchments, despite their small drainage areas. We constructed an empirical model relating baseflow discharge to catchment area within the watershed. We quantified long-term (103-104 yrs) catchment erosion from 10Be in sediment and measured the short-term volumetric flux of bedload transport at baseflow. Rates of transport and erosion in this group of channels scale linearly with the feeding drainage area and baseflow discharge. This finding supports a stream incision model proposed for groundwater-driven channels (Howard, 1995). We propose that deepening saprolite and coincident entrenchment of the subsurface water-routing system initiated seepage erosion and are actively expanding the headwaters in the Rio Blanco.Plain Language Summary The relationship between landforms and the processes that shape them on Earth can be used to identify the processes at work in places that can only be studied remotely, like the deep ocean or the surface of other planets. In the early 1980s, researchers recognized that river channels have different shapes depending on whether they are carved by water moving over the land surface or flowing underground. Early studies of groundwater erosion in sandbox models found that there is a unique relationship between erosion and the rate of groundwater flow into a channel that does not exist under other circumstances. However, this relationship has yet to be verified in natural landscapes. In this study, we measured the shape-properties, groundwater flow, and erosion rates over short (hours) and long (tens of thousands of years) timescales in the headwater channels of steep, mountain rivers in a tropical rainforest in Puerto Rico. We identified a distinctive population of streams with geometric properties and stream flow-to-erosion rate relationship that match predictions for channels carved by water flowing underground on both short and long timescales. This is the first study investigating groundwater-driven erosion using Be-10 as a direct geochemical tracer.Key PointsMorphology of channels mimics theoretical expectations of groundwater-driven erosion Baseflow discharge from springs can transport the fluvial bedload Long-term erosion rates scale linearly with baseflow discharge rates