Volume 3 Issue 7, July 2010

The mechanics of slip on faults in the Earth's crust are still unclear. Field observations from New Zealand show that movement can occur where — according to conventional assumptions of fault strength — it should not be possible.

Pine Island Glacier on West Antarctica's Amundsen Sea coast has experienced accelerating retreat over the past few decades. Oceanographic observations under the associated ice shelf show how changes in water flow and ice-cavity geometry have contributed to ice melting.

The northern plains of Mars are thought to have harboured an ocean more than 3.6 billion years ago. Delta deposits and river-valley termini ring the proposed seabed and define an equipotential palaeoshoreline.

The timing and nature of changes in the chemistry of the early oceans are intensely debated. Geochemical analyses show that a prominent transition to sulphidic marine conditions 1.8 billion years ago may have been restricted to near-shore environments.

Most of the oceanic crust has a simple layered structure. The discovery that slow-spreading ridges exhibit a comparatively complex crustal structure and some of the largest extensional faults on Earth is leading to the recognition of a new mode of seafloor spreading.

Direct evidence for the role of volatiles in magmatic ore formation has been elusive. Magma degassing at Merapi volcano in Indonesia is found to be directly linked to the selective leaching of metals from sulphide melts that ultimately form ore deposits.

The climate of early Mars could have supported a complex hydrological system. Analysis of ancient deltaic deposits and valley networks reveals the presence of a planet-wide equipotential surface in the northern lowlands, indicative of the existence of a vast ocean on Mars 3.5 billion years ago.

Sequestration of carbon dioxide has been proposed for the mitigation of ongoing global warming. Projections with an Earth system model over 100,000 years suggest that leakage from carbon-storage reservoirs of no more than 1% per thousand years, or continuous resequestration, would be required to maintain conditions similar to a low-emissions scenario.

Thinning ice in West Antarctica is currently contributing about 10% of the observed rise in global sea level. Observations obtained from an autonomous underwater vehicle operating beneath Pine Island Glacier, West Antarctica, reveal that the glacier was recently grounded on a transverse ridge in the sea floor, but now warm sea water flows through the widening gap above the ridge.

Methylmercury is a neurotoxin that accumulates in food webs and poses a significant risk to human health. Laboratory experiments suggest that complexation of methylmercury with sulphur-containing ligands can stimulate its degradation.

River canyons are thought to be cut slowly over millions of years. However, at Lake Canyon Gorge, Texas, a seven-metre-deep canyon was cut in just three days in 2002, providing insight into the erosion processes operating during megaflood events.

Some faults slip at high angles to the greatest principal compressive stress. The discovery of shear veins formed at angles of about 80 degrees relative to the greatest principal compressive stress in the Chrystalls Beach complex, New Zealand, suggests that slip can be facilitated by a pre-existing rock fabric under high fluid pressure.

The deposition of iron formations ceased about 1.84 billion years ago. Reconstructions of ocean chemistry suggest that the advent of euxinic conditions along ocean margins preferentially removed dissolved iron from the water column in the form of the mineral pyrite, inhibiting widespread iron-oxide mineral deposition.

Extension at mid-ocean ridges can be accommodated by detachment faults, forming oceanic core complexes that develop under low rates of magma intrusion. Modelling reveals that oceanic core complexes can also form under high rates of magma intrusion, if the magma is injected into the lower ductile layer of the crust.

A large earthquake has been a national hazard concern for decades in the Tokai region of Japan. The 2009 Suruga Bay earthquake increased seismic stress in strongly locked patches of the Tokai fault plane, potentially increasing the likelihood of a major earthquake in the region.

The metal content of ore deposits formed during subduction-zone volcanism was thought to be established when the ore fluid separates from the parent magma. Analyses of metal concentrations in erupted melts and the volcanic gases emitted after an eruption in Indonesia reveal that metals can be added to the ore fluid later, during mixing with separated melts.

In an attempt to assess the factors controlling the rates of glacial melt in West Antarctica, Adrian Jenkins and colleagues found themselves waiting anxiously for their submersible, Autosub3, to return from under an ice shelf.