Volume 6 Issue 5, May 2013

The fault zone that hosted the devastating Wenchuan earthquake in 2008 had been assigned a moderate-to-low seismic hazard rating, because it slips slowly. In hindsight, it seems that this type of fault is not necessarily innocuous.

The catastrophic Wenchuan earthquake induced an unprecedented number of geohazards. The risk of heightened landslide frequency after a quake, with potential secondary effects such as river damming and subsequent floods, needs more focused attention.

The 2008 Wenchuan earthquake highlights some of the successes of government-led schemes to mitigate the impact of natural disasters. A stronger focus on individuals and local communities could reduce losses even further in the future.

Snow and ice influence the climate and chemistry of the polar atmosphere. Field experiments in Alaska point to the significance of surface snow for polar ozone depletion events.

Volcanic rocks erupted at mid-ocean ridges can record the temperature of the underlying mantle. Ancient crust in the Atlantic Ocean formed from anomalously hot mantle, possibly warmed by continental insulation before the opening of the ocean basin.

Antarctic climate has undergone substantial shifts in past decades, but whether these changes are unusual in the long term is unclear. Ice-core records suggest that some aspects of this variability are unique to the past two millennia.

Sinking slabs of oceanic lithosphere often stagnate in Earth's mantle. Experiments show that common slab minerals transform to their high-pressure, high-density counterparts at very slow rates, thus keeping the slabs buoyant and impeding subduction.

Rainfall disparities are expected to intensify in response to anthropogenic climate change. Model simulations suggest that wet regions and seasons will get wetter, and that a warmer equator will get wetter too.

Temperature change over the past 2,000 years has shown pronounced regional variability. An assessment of all available continental temperature reconstructions shows a clear twentieth century warming trend, but no evidence of a coherent Little Ice Age or Medieval Warm Period.

Saturn is brighter than expected for a gas giant of its age. Calculations of Saturn’s thermal evolution show that the presence of layered convection in Saturn’s interior—much like that observed in the Earth’s oceans—would have slowed the planet’s cooling and may explain Saturn’s anomalous luminosity.

Following the spring-time polar sunrise, ozone concentrations in the lower troposphere episodically decline to near-zero levels. Measurements on Alaskan snow and sea ice suggest that photochemical reactions in surface snow serve as a major source of reactive bromine to the overlying atmosphere, contributing to episodic ozone depletion.

The response of tropical precipitation to global warming varies spatially and the factors controlling the spatial patterns of precipitation changes are unclear. An analysis of climate model simulations shows that warm regions are projected to become wetter in annual mean, whereas seasonally high rainfall anomalies are expected in regions that are currently wet.

Multi-decadal variability in coral growth rates has been documented throughout the Caribbean over the past 150–200 years. Analyses of observational and model data suggest that anthropogenic aerosols were a key driver of variations in coral growth in the western Caribbean in the second half of the twentieth century.

In the Antarctic interior, assessments of surface mass balance may overestimate accumulation because high winds remove some of the annual snowfall. Geophysical observations reveal localized zones of persistent wind scour (where little or no snow accumulates) that are predicted to occur across approximately 5% of the Antarctic surface.

Whether changes in atmospheric circulation over West Antarctica during the past few decades are part of a longer-term trend is unclear. Ice cores reveal a significant increase in the oxygen isotopes from precipitation over the past 50 years, but the anomaly cannot be distinguished from natural climate variability.

In sharp contrast to events in the Arctic region, sea ice surrounding Antarctica has expanded slightly in the past few years. A combination of observations and climate model simulations suggests that cooling of the surface ocean by meltwater from the Antarctic ice shelves has contributed significantly to this sea ice expansion.

The growth of ice on Antarctica about 34 million years ago affected sea level. A combination of modelling and marine sediment analyses shows that sea level near the developing ice sheet first fell and then rose as a result of crustal deformation imposed by the ice growth.

Lavas erupted from individual volcanic centres often have one of two distinct compositions. High pressure and temperature experiments on lava samples collected from St Vincent Volcano in the Caribbean, combined with thermal modelling, show that this compositional bimodality is generated by volcanic systems with low heat and water content.

The continents are thought to insulate and heat the underlying mantle. Geochemical analyses of lava samples formed at a mid-ocean ridge in the Atlantic Ocean immediately after continental breakup show that the mantle was up to 150 °C hotter than today and took about 70 million years to cool.

In the northwestern United States, two neighbouring volcanic chains—the Snake River Plain and High Lava Plains—decrease in age in opposing directions. Laboratory experiments show that diverging volcanic chains can form where vigorous mantle circulation beneath a subduction zone causes an upwelling mantle plume to split into two.

Subducting slabs of oceanic lithosphere often stagnate before reaching the lower mantle. Laboratory experiments under high pressures and temperatures show that pyroxene, a common mineral in such slabs, is transformed to its dense, high-pressure counterpart, majorite garnet, at a very slow rate, temporarily keeping the slabs buoyant compared to the surrounding mantle.

The Antarctic Peninsula is one of the most rapidly warming regions on Earth. A reconstruction of ice melt from an ice core taken near the northeastern tip of the peninsula over the past 2,000 years shows that surface melt has accelerated during the twentieth century.

The Wenchuan earthquake that occurred in southwest China on 12 May 2008 killed more than 80,000 people and displaced millions. Five years on, many of the affected communities have made a good recovery – at least until the most recent quake in April 2013 wreaked further havoc in the region. The devastating 2008 event has helped invigorate research into earthquake hazards. A collection of opinion pieces, published in Nature Geoscienceto mark the fifth anniversary of the 2008 event, discusses the mechanisms for the Wenchuan quake itself and the implications for our understanding of the eastern margin of the Tibetan Plateau, the ongoing risk from quake-induced landslides, and the societal impacts of the earthquake.