Kevin M. Befus

Devastation of aquifers from tsunami‐like storm surge by Supertyphoon Haiyan

The northwest Pacific Ocean is a hot spot for sea level rise and increasing frequency of stronger storms. It is where Supertyphoon Haiyan formed, the strongest storm to hit land, which provided a window into the hydrologic impacts of an extreme storm. Through detailed documentation of flood levels, groundwater table elevations and salinity, electrical resistivity, and modeling, we found that Haiyans storm surge reached 7 m above sea level along Samar Island, Philippines, which led to contamination of crucial aquifers by infiltrating seawater. A contaminated surficial aquifer will take years to recover. Groundwater in an underlying deeper aquifer saw widespread contamination immediately after the storm, but here salinity has decreased significantly after 8 months. However, this deeper aquifer remains vulnerable to seawater slowly percolating through the surficial aquifer. As warmer seas generate more powerful storms, the vulnerability of aquifers to persistent contamination from intense storm surges is a growing concern for coastal communities.

Classification and delineation of groundwater–lake interactions in the Nebraska Sand Hills (USA) using electrical resistivity patterns

Lake–groundwater interactions exhibit a complex three-dimensional (3D) structure that is seldom studied. The utility of waterborne electrical resistivity (ER) surveys is explored for characterization of 3D groundwater flow and solute transport patterns for three lakes in the Nebraska Sand Hills, USA. Waterborne ER surveys, using contrasts between lake and groundwater solutes as natural tracers, are useful for inferring 3D patterns of groundwater flow and solute transport as well as classifying groundwater–lake interactions. Three unique groundwater flow systems are interpreted under each lake from dense networks of two-dimensional (2D) waterborne ER surveys. A lateral transition from high to low ER values beneath the saline Wilson Lake expresses its flow-through regime, where groundwater salinity indicates changes from groundwater inflow to outflow. Alkali Lake ER profiles reveal a prevalent ER increase with depth over the lakebed area that is characteristic of groundwater discharge lakes. ER profiles beneath Gimlet Lake are the most resistive and indicate pockets of high ER related to fresh groundwater discharge into the lake, supporting a flow-through regime with a short flushing time. These ER patterns correctly classify groundwater–lake interactions and provide high spatial resolution of mixing patterns for systems with varying water salinity.RésuméLes interactions eau de nappe–lac présentent une structure tridimensionnelle (3D) complexe qui est rarement étudiée. L’utilité de levers de résistivité électrique (RE) hydro portés est explorée pour caractériser un flux de nappe 3D et pour établir les caractéristiques d’écoulement de trois lacs dans les Sand Hills du Nebraska, USA. Les relevés RE hydro portés, utilisant les contrastes entre solutés du lac et solutés de l’eau souterraine en tant que traceurs naturels, sont utiles pour inférer les caractéristiques 3D du flux de nappe et transport de soluté comme pour comprendre et classer les interactions eau de nappe-lac. Trois systèmes singuliers de flux souterrains sont caractérisés sous chaque lac à partir d’un réseau dense de relevés RE 2D hydro portés. Une transition latérale de haute à basse valeur de RE sous le lac salé Wilson exprime un régime d’écoulement partagé, où la salinité de l’eau de nappe indique les changements de flux entrants et sortants. Les profils RE sur Akali Lake révèlent qu’une augmentation de RE prévaut avec la profondeur, ce qui est caractéristique des lacs de décharge de nappe. Les profils RE sous Gimlet Lake sont les plus résistants et indiquent des poches de RE élevée en relation avec une décharge d’eau douce dans le lac, siège d’un régime d’écoulement partagé avec un flux rapide. Ces caractéristiques de RE classent correctement les interactions eau de nappe– lac et fournissent en haute résolution spatiale les caractéristiques de systèmes imbriqués à eaux de salinité variable.ResumenLas interacciones entre agua subterránea–lago exhibe una estructura compleja tridimensional (3D) que raramente es estudiada. Se exploró la utilidad de los sondeos de resistividad eléctrica (ER) basados en el agua para la caracterización de los esquemas de flujo de agua subterránea 3D y de transporte de soluto para tres lagos en Nebraska Sand Hills, EEUU. Los sondeos ER basados en el agua, usando contrastes entre los solutos del agua del lago y el subterránea como trazadores naturales, son útiles para inferir esquemas 3D del flujo de agua subterránea y del transporte de solutos así como para clasificar las interacciones agua subterránea–lago. A partir de redes densas de sondeos ER basados en el agua se interpretaron tres sistemas únicos de flujo de agua subterránea bajo de cada lago. Una transición lateral desde altos a bajos valores debajo del lago salino Wilson expresa su régimen de flujo continuo a través del medio, donde la salinidad del agua subterránea indica cambios desde la entrada de agua subterránea hasta su salida. Los perfiles ER del lago Alkali revelan un predominio de incremento de ER con la profundidad sobre el área del lecho del lago que es característico de lagos de descarga de agua subterránea. Los perfiles ER debajo del lago Gimlet son los más resistivos e indican bolsas de alta ER relacionados a la descarga de agua subterránea dulce en el lago, manteniendo un régimen continuo de flujo con un tiempo corto de lavado. Estos esquemas de ER clasifican correctamente las interacciones lago–agua subterránea y proporcionan una alta resolución espacial de los esquemas de mezcla para sistemas con salinidades del agua variables.摘要湖水地下水相互作用显示为一种复杂的、很少被研究过的三维结构。本文在美国内布拉斯加州沙丘开展了水上电阻率(ER)调查以刻画三个湖泊的三维地下水流和溶质运移特征。水上ER调查是利用湖水和地下水溶质的差异作为天然示踪剂,在推断地下水流和溶质运移的三维形态以及划分地下水湖水相互作用方面非常有用。通过高密度2维水上ER调查,在每个湖泊下面解译出了3种独立的地下水流系统。在Wilson咸湖下面ER值从高到低的侧向过渡,显示了它的水流动态,在这里用地下水盐度指示地下水流入到流出的变化。Alkali湖ER剖面显示出在湖床上ER随深度增加而升高的趋势,为地下水向湖排泄的特征。Gimlet湖的ER剖面电阻率最高,高ER区与地下淡水向湖的排泄有关,支持短时间内水流通过的推断。ER的分布特征恰当准确的划分了地下水湖水相互作用,且提供了高空间分辨率的不同盐度的地下水混合形态特征。ResumoAs interações lago–água subterrânea exibem uma complexa estrutura tri-dimensional (3D) que é frequentemente estudada. A utilidade de campanhas de resistividade elétrica (RE) em meio aquoso é explorada para caraterizar o fluxo subterrâneo 3D e os padrões de transporte de solutos em três lagos nas Montanhas de Nebraska Sand, EUA. As campanhas de RE em meio aquoso, usando os contrastes entre a concentração de solutos do lago e da água subterrânea como traçadores naturais, são úteis para inferir os padrões 3D do fluxo subterrâneo e transporte de solutos, bem como para classificar as interações água subterrânea-lago. A partir de densas redes de campanhas de RE 2D em meio aquoso, foram interpretados três sistemas únicos de fluxo subterrâneo subjacentes a cada lago. A transição lateral de elevados valores para baixos valores de RE debaixo do lago salino de Wilson reflete o seu regime de passagem de água, onde a salinidade da água subterrânea indica mudanças entre entradas e saídas de água subterrânea. Os perfis de RE do Lago Alkali revelam a prevalência de um aumento da RE com a profundidade ao longo da área do leito do lago, o que é caraterístico de lagos com descarga de água subterrânea. Os perfis de RE debaixo do Lago Gimlet são os mais resistivos e indicam a existência de zonas com elevada RE, relacionadas com a descarga de água doce subterrânea no lago, o que reflete um regime de passagem de água com um curto período de renovação. Estes padrões de RE permitem classificar corretamente as interações água subterrânea–lago e fornecem uma elevada resolução espacial dos padrões de mistura em sistemas com águas de diferentes salinidades.

Spherulites as in-situ recorders of thermal history in lava flows

Spherulites in rhyolitic obsidian provide a record of the thermal history of their host lava during the interval of spherulite growth. We use trace element concentration profiles across spherulites and into the obsidian host from Yellowstone National Park (USA) to reconstruct the conditions that existed during spherulite formation. The measured transects reveal three behaviors: expulsion of the most diffusively mobile elements from spherulites with no concentration gradients in the surrounding glass (type 1); enrichment of slower-diffusing elements around spherulites, with concentration gradients extending outward into the glass (type 2); and complete entrapment of the slowest-diffusing elements by the spherulite (type 3). We compare the concentration profiles, measured by laser ablation–inductively coupled plasma–mass spectrometry and Fourier transform infrared spectroscopy, to the output of a spherulite growth model that incorporates known diffusion parameters, the temperature interval of spherulite growth, the cooling rate of the lava, and data on the temporal evolution of spherulite radius. Our results constrain spherulite nucleation to the temperature interval 700–550 °C and spherulite growth to 700–400 °C in a portion of lava that cooled at 10 –5.2 ± 0.3 °C s –1 , which matches an independent experimental estimate of 10 –5.3 °C s –1 measured using differential scanning calorimetry. Maximum spherulite growth rates at nucleation are on the order of 1 μm hr –1 and are inferred to decrease exponentially with time. Hence, spherulites may serve as valuable in-situ recorders of the thermal history of lava flows.

The rapid yet uneven turnover of Earth's groundwater†

The turnover of groundwater through recharge drives many processes throughout Earths surface and subsurface. Yet groundwater turnover rates and their relationship to regional climate and geology remain largely unknown. We estimated that over 200 million km3 of groundwater has recharged since the Last Glacial Maximum (LGM), which is ten times the volume of global groundwater storage. However, flushing is very unevenly distributed throughout Earths one million watersheds, with some aquifers turned over thousands of times to others with <1% turnover. The median global groundwater turnover of 5 ± 3 times since the LGM highlights groundwaters active role in earth system processes. Incomplete groundwater turnover since the LGM beneath a third of land areas reveals the imprint of relict climate conditions on modern-day groundwater resources. The bulk groundwater turnover calculated here enable better quantification of groundwaters impact in dynamic global water budgets and the transport of nutrients, contaminants, and geologic weathering products.

The Magnitude and Origin of Groundwater Discharge to Eastern U.S. and Gulf of Mexico Coastal Waters

Fresh groundwater discharge to coastal environments contribute to the physical and chemical conditions of coastal waters, but the roles of coastal groundwater at regional to continental scales remains poorly defined due to diverse hydrologic conditions and the difficulty of tracking coastal groundwater flow paths through heterogeneous subsurface materials. We use three-dimensional groundwater flow models for the first time to calculate the magnitude and source areas of groundwater discharge from unconfined aquifers to coastal waterbodies along the entire eastern U.S. We find 27.1 km3/yr (22.8-30.5 km3/yr) of groundwater directly enters eastern U.S. and Gulf of Mexico coastal waters. The contributing recharge areas comprised ~175,000 km2 of U.S. land area, extending several kilometers inland. This result provides new information on the land area that can supply natural and anthropogenic constituents to coastal waters via groundwater discharge, thereby defining the subterranean domain potentially affecting coastal chemical budgets and ecosystem processes.