1.Secret chamber under Old Faithful drives eruptions 11:18 12 April 2013 by Nicola Jones

The Old Faithful geyser in Yellowstone national park is famed for its clockwork eruptions – every 90 minutes, on average. Now a secret chamber has been found in the rocks beneath the geyser, radically changing our understanding of how it erupts.

In the early 1990s, researchers lowered a camera into Old Faithful's throat and, 7 metres down, saw a "choke-point" less than 10 centimetres wide. Below that was a cavern about the size of a small car. But the camera couldn't go deeper than 14 metres because of the violent churn of boiling fluids.

Now Jean Vandemeulebrouck of the University of Savoie in Le Bourget du Lac, France, and colleagues have analysed seismic data collected in the 1990s. Using a modern

acoustic technique more commonly used to locate whales or submarines, they analysed the noise of the popping bubbles inside the geyser – captured in the seismic record – to reveal a 60-cubic-metre cavern 15 metres down, and off to the geyser's side.

This side cavity acts as a compressible reservoir, making the water in the smaller main vent bob up and down like a spring. The oscillations affect the water pressure and help the geyser to boil in the early stages of eruption.

The side cavern "totally changes our perspective of the physics of how geysers work", says Shaul Hurwitz, a hydrologist with the US Geological Survey in Menlo Park,

California, who hopes the innovative acoustic technique can be applied to visualising the insides of volcanoes as well as geysers.

2.New York at high risk of alien invasions

17:34 07 May 2013 by Fred Pearce Magazine issue 2916. Subscribe and save

Aliens don't strike everywhere in equal measure. The first comprehensive assessment of the risk posed by ballast water has identified 20 hotspots that are particularly vulnerable to being invaded by species stowed away inside the bowels of cargo ships.

San Francisco Bay, New York, Los Angeles, Hong Kong and Durban in South Africa are on the list, which could help focus counter-measures.

Empty ships routinely take on seawater as ballast before they set sail, to keep them

stable while at sea. They later dump it in the port where they take on cargo. At any one time, an estimated 7 billion tonnes of ballast water is crossing the oceans – almost all of it