Fractured rocks play central role in a wide variety of environmental fields including hydrogeology, geothermal energy, hydrocarbon extraction, and long-term storage of toxic waste. In these and other applications, the presence of fractures has dramatic consequences because they form highly permeable structures that can both help to extract the resource and lead to a faster and further migration of subsurface pollutants.
Mine wastes are of tremendous environmental concern because of their high concentrations in radioactive and toxic elements and persistence in groundwater. Despite attempted surface remediation of contaminated sites, extensive contamination remains in sediments and groundwater in France and the U.S. Little is known about the chemical stability of uranium and other toxic metals in these contaminated materials. Moreover, remediation strategies are lacking.
Unlike the surface currents that have been extensively studied thanks to satellite observations, the oceanic deep circulation is poorly known. In the tropics, observational cruises have revealed the presence of energetic currents, which are able to transport and mix water masses and their biogeochemical properties, such as the oxygen content.
One of the most important tasks of earthquake seismology is to predict the intensity of shaking in large earthquakes. With that, engineers have the information needed to design earthquake-resistant structures, and policymakers have the information needed to develop effective mitigation and response strategies. To predict ground shaking from earthquakes accurately, we describe the full behavior of seismic wave propagation through the Earth using the Green’s function.
The Earth was extensively molten in the first 100 million years after its formation. In that span of time, it acquired much of its present-day structure: the metallic core segregated and sank towards the center, while the mantle and crust separated at the surface. The primordial evolution of the mantle and core can be thought of as the most ancient and most global magmatic differentiation event in Earth’s history; it involves the solidification of the molten planet, also known as the “Magma Ocean”.
Geoscientists and engineers use mineral and glass dissolution rates to quantify waterrock interactions and make predictions about groundwater chemistry, energy systems and environmentally contaminated sites. However, such rates are typically laboratory-derived and differ dramatically from observed rates in natural settings.
Since the Industrial Revolution, nearly 90% of the excess heat trapped by greenhouse gasses and around half of the carbon released by humans have entered the ocean. Knowing where and for how long this heat and carbon is stored in the ocean is critical for predicting climate variability, and is strongly shaped by the ocean’s abyssal circulation. A key branch of this circulation upwells water from the deep equatorial Pacific and is driven by turbulent mixing. However, the source of this turbulence is not well understood.
Oxygen first appeared in the Earth’s atmosphere approximately two billion years ago, during the “Great Oxygenation Event”, setting the stage for the evolution of increasingly complex life. Shortly afterward, O2 concentrations declined to very low, but non-zero values, referred to as the “Oxygen Overshoot”. However, it is unclear whether the decline occurred rapidly or over tens of millions of years, and how much O2 levels decreased. To better understand the evolution of O2 during this critical interval, I will collaborate with Dr.
How do abyssal waters get back to the surface? This question has puzzled oceanographers for years. At Stanford, we developed a theory according to which equatorially trapped waves1 propagate down into the ocean abyss, essentially break upon reflection off the sea floor, and thus mix water from the deep up towards the surface. The encounter between this old water from the deep and the sea surface can result in large exchanges of CO2 and heat between the ocean and atmosphere, with implications for climate.