Volume 6 Issue 8, August 2013

Geological and biological processes have eliminated all but the faintest traces of our earliest ancestors on Earth. To understand the origin of life, we must investigate other planets — but we can find what we seek only if we do not contaminate them with Earth life first.

Subduction zone earthquakes cause the overriding plate to stretch and subside. Excessive subsidence of volcanoes during the large quakes in Chile in 2010 and Japan in 2011 highlight an unexpected response of volcanic areas to the sudden tectonic pull.

The Indonesian government ruled that the Lusi mud eruption was triggered by drilling and held an oil company responsible. Instead, a curved rock layer capping the mud reservoir may have amplified passing seismic waves and the trigger may have been natural.

Interactions between the ocean and atmosphere are complex. An analysis of satellite data from the Southern Ocean reveals a tight coupling of ocean and atmosphere on horizontal scales of around 100 km that modifies both near-surface winds and ocean circulation.

The extinction of megafauna in Australia roughly coincided with shifts in vegetation and fire regimes. Sediment geochemistry shows that the vegetation shift followed the extinction, indicating that the loss of browsers promoted fire and altered plant composition.

A substantial amount of atmospheric carbon taken up on land is transported laterally from upland terrestrial ecosystems to the ocean. A synthesis of the available literature suggests that human activities have significantly increased soil carbon inputs to inland waters, but have only slightly affected carbon delivery to the open ocean.

Owing to the turbulent nature of the ocean, mesoscale eddies are omnipresent. An analysis of atmospheric conditions associated with several hundred thousand eddies in the Southern Ocean suggests that the transitory sea surface temperature fronts associated with these eddies alter near-surface winds, clouds and rainfall.

The Greenland and Antarctic ice sheets have been reported to be losing mass at accelerating rates. Comparison of mass loss trends over the past decade with reconstructions of past mass loss indicates that the existing satellite record is too short to separate long-term mass loss trends from natural variability.

Over the twentieth century, droughts in southwestern North America have been linked to sea surface temperature variability in the North Pacific Ocean. Speleothem data from southern California suggest that links between the North Pacific and drought were less pronounced during the past millennium.

During the last deglaciation, the North Pacific Ocean was characterized by a spike in primary productivity, which has been attributed to iron input. Marine sediment analyses suggest that, instead, the productivity may have been fuelled by deep convection and subsequent stratification.

The extinction of megafauna in Australia about 43,000 years ago has been linked to both human arrival and vegetation change. Marine sediment analyses from the east coast of Australia suggest that vegetation change was a result, rather than cause, of the extinction.

Large earthquakes in subduction zones can affect nearby volcanoes. Analysis of ground deformation following the 2010 earthquake in Maule, Chile, shows that some volcanoes subsided by up to 15 cm, probably because of quake-triggered release of hydrothermal fluids.

The 2011 Tohoku earthquake caused high levels of crustal deformation in Japan. Analysis of satellite radar and GPS data show that the earthquake caused nearby volcanic regions to subside instantaneously, creating elliptical depressions that are parallel to the direction of quake-induced crustal extension.

The Lusi mud eruption in Indonesia has been ongoing since 2006. Numerical simulations show that a parabolic-shaped layer in the rock surrounding the site of the Lusi eruption could have amplified and focussed incoming seismic energy from an earthquake, which then triggered the mud eruption.

Methane is abundant in marine sediments. Analysis of sediment cores and seismic images of marine sediments obtained off the coast of Pakistan show fracturing of gas hydrates and an increase in upward methane flux in the decades following a large earthquake in the Arabian Sea in 1945, suggesting that quakes can trigger hydrocarbon seepage.

Volcanic tremor can be caused by small earthquakes occurring within the volcano. Mechanical modelling of volcanic tremor generated at Redoubt Volcano, Alaska, suggests that high-frequency tremor is the result of stick–slip motion in faults within the volcano conduit.

The precise location of the mantle plume upwelling beneath Hawaii is debated. Seismic data reveal a thick layer of melt in the mantle beneath western Hawaii, implying that the upwelling plume may be deflected around an ancient, resistive root beneath the island.

As a moist atmosphere warms, it will reach a limit after which it is unable to radiate incoming solar radiation back to space, and a runaway greenhouse will occur. Calculations suggest that this limit is lower than previously thought and, for a water-saturated atmosphere, a runaway greenhouse can occur under present-day solar radiation.

Ocean Anoxic Event 2 was marked by rapid global warming and loss of O₂ from the ocean. Lithium isotope data suggest that the warming was accompanied by enhanced silicate weathering, which stimulated marine productivity and helped stabilize atmospheric CO₂ levels.

Earthquakes have long been known to trigger more earthquakes, as well as volcanic eruptions and landslides. In this web focus, we present opinion pieces and primary research articles that document and discuss a range of additional, less obvious links between earthquakes and other geological spectacles — such as volcaNo. sinking, seafloor gas-hydrate escape and a mud eruption — that have only now come into focus.