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 Haiyan's 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.

On 17 February 2006, a rockslide-debris avalanche cascaded down the steep slope of Mt. Can-abag, burying the entire village of Guinsaugon in St. Bernard, Southern Leyte, Philippines.Casualties include 139 dead with 980 still missing and presumed dead, making it perhaps the most catastrophic landslide in Philippine history. The landslide started at the ridge top along a fault plane associated with the active Philippine Fault Zone. It started as a block slide that transformed into an avalanche. The entire event lasted for only a few minutes. Estimated maximum landslide velocity is 120-130 m/s. The landslide left behind a deep, wedge-shaped scarp. The central part of the deposit exhibits a hummocky topography typical of avalanches, in contrast to the flatter surface of the debris-flow-type marginal deposit. High amounts of soil in the matrix were derived from the scouring of ancient landslide deposits and rice fields in the valley. The landslide has a total area of 3.2 km 2 and a runout distance of 4.1 km. Estimated volume of debris is approximately 20 Mm 3 . At least four streams were dammed by the landslide debris. Intense precipitation and earthquakes preceding the landslide are the potential triggers. Preliminary back analyses assuming a planar and wedge slip surface yielded very low factors of safety even under dry conditions. A more rigorous analysis of the failure mechanism of the landslide is needed.

We investigated submarine groundwater discharge (SGD) in a volcanic coastal area that hosts the world's most biodiverse reefs. Measurements of 222Rn activity in coastal seawater, a tracer for groundwater, indicated prevalent SGD. In areas where seawater 222Rn activity was generally higher, we discovered hydrothermal springs emitting acidic waters (pH ~5.4–6.0) and venting magmatic CO2 that brought local pCO2 levels up to 95,000 ppm. The collection of vents raised CO2 and lowered pH over 1–2 km of coastline. The hydrogen and oxygen isotope compositions of water and chloride concentration revealed that the springs discharge recirculated seawater mixed variably with terrestrial groundwater. Shallower springs and pore water have a higher proportion of terrestrial groundwater than deeper springs, which emit mostly recirculated seawater. This suggests that different SGD mechanisms are present. The SGD could be contributing to the evolution and function of the biodiverse ecosystem, but it also represents myriad pathways for contamination.

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[1] Thermal springs are ubiquitous features whose underground kinematic structure is mostly unknown but are typically thought to originate from deep sources. We documented a type of thermal springs at the banks of a volcanic lake that are discharge zones of hydrothermal convection cells circulating groundwater within the near shore environment. The convection captures lake water through the lakebed, mixes it with deeper groundwater at velocities of 100s of m d À1, then returns the water to the lake via the spring. The convection cell is flushed in a few hours and turns over the lake's volume in a few days. Most volcanic lakes and other relatively cool surface water bodies in areas of elevated geothermal heat fluxes meet the conditions for the occurrence of local hydrothermal circulation of groundwater. The type of spring we studied, the terrestrial version of black smokers, is likely present but perhaps unrecognized at many areas. Citation: