Shock waves from ancient lunar impacts may be responsible for creating the Earth’s single most famous face – the “Man in the Moon”.

People have long interpreted a series of dark patches on the Moon’s surface as a human face but no one knew how they formed. Now, scientists at Ohio State University, US, appear to have solved the mystery by creating a topographical model of the Moon and mapping gravity signatures of rocks all the way to the core.

Their findings suggest that the impacts of ancient collisions on the far side of the Moon were so great they caused a corresponding bulge on the near side, and the Earth’s gravitational pull further tugged at this bulge.

Those colossal movements opened cracks in the crust and let magma from the lunar mantle flood onto the surface, at a time when the Moon was still geologically active. This solidified to form what we now see from Earth as the eyes, nose and mouth of the Man in the Moon.

Rocked to the core

“Where you have impact craters, you get an anomalous distribution of mass, and that’s what shows up on the gravity field model,” explains Ralph von Frese, a geologist at Ohio State, and one of the team.

“The impacts were huge enough to disrupt the Moon to its core and at the same time Earth’s gravity field moved mass preferentially to the nearside. Because this happened when the Moon was solidifying, the movements of mass produced a gravity anomaly that we can measure four billion years later.”

The researchers used gravity fluctuations measured by NASA’s Clementine and Lunar Prospector satellites to map the moon’s interior.

Journal reference: Physics of the Earth and Planetary Interiors (DOI: 10.1016/j.pepi.2005.06.013)

Other areas in danger include havens of biodiversity such as the Red Sea and the pristine coral islands of the western Indian Ocean.

The map is the first of its kind. Its creators hope governments will use it to prioritise resources and reduce the damage caused to the environment from future spills. Between 1993 and 2002, 580,000 tonnes of oil spilt into the sea in 470 separate accidents.

Their seriousness depended on the amount and type of oil involved, the weather and sea conditions, the depth of the water and nature of the seabed, and the effectiveness with which the relevant authorities responded.

Transport routes

To create the map, Helen Thomas at the International Tanker Owners Pollution Federation (ITOPF) plotted the routes used to transport oil in 2001, locations of spills from 1974 to the present day, and the causes of past spills.

Technical advisers at ITOPF then rated each region on a scale of 1 to 3, with 1 representing a low risk and 3 a high one, says project manager Tosh Moller. The highest-risk regions at this stage included the waters around the UK, the Mediterranean, and the north-west Pacific.

The next stage was to assess whether countries in each region are ready to tackle an oil spill, by checking which nations have ratified international agreements such as the Oil Pollution Preparedness, Response and Cooperation Convention. The ITOPF analysis showed, for instance, that long stretches of Africa’s coastline have no adequate disaster recovery plans.

Degraded environment

Combining the two sets of data yielded a composite map that showed where the risk was high compared with low preparedness. Turkey has been warning of the risk facing the Black Sea since 1998, following 150 oil-related accidents in the region in a decade.

In one of the most serious, in 1994, an oil tanker collided with another vessel, resulting in the death of 28 seamen and a 15,000-tonne spillage that caught fire. The Black Sea is already considered to be the most degraded marine environment in Europe.

“These results are preliminary, and there’s a lot more in-depth work to do, but in time we hope to publish the work to help organisations such as the International Maritime Organization and UN Environment Programme’s Regional Seas programme to prioritise their resources,” says Thomas.

Even the devastating floods that left cities from Prague to Dresden awash with water in 2002 do not suggest an upward trend, Manfred Mudelsee at the University of Leipzig and his colleagues found.

Many reports at the time suggested that the floods were the kind of extreme weather event expected to become more frequent as a result of global warming. But “if they can’t find trends, then there is no reason to attribute the flooding to climate change” says Mike Blackburn, a climate scientist at the University of Reading, UK.

However, while the frequency of major floods may not be increasing, the economic damage and the number of people at risk of flooding may well be going up. This is due to, for example changes in land-use and in the possessions damaged by flooding.

The damage caused by the 2002 floods cost the insurance industry $4.1 billion, says Jens Mehlhorn, head of the flood group at Swiss Re in Zurich. The average loss over the previous 15 years was $1 billion a year, and there is an “upward trend in losses”.

“People now live in more risky areas and the vulnerability of the insured objects has increased – for example if a PC or television gets wet, you have to throw it away,” he told żěè¶ĚĘÓƵ.

Elbe and Oder

The University of Leipzig study focused on two rivers – the Elbe and the Oder. It was the Elbe, which flows from the Czech Republic, through Germany and into the North Sea, which was responsible for the flooding in the summer of 2002. The Oder also emerges in the Czech republic and runs northwards. Together they drain rainfall from 150,000 square kilometres of central Europe.

Mudelsee found evidence for 328 major floods on the Elbe, with the earliest in 1021, and 218 floods on the Oder, beginning in 1269. “We then applied a statistical test to see if we could find a significant trend over the last few decades” he told żěè¶ĚĘÓƵ.

There was no trend at all in summer floods, while those in winter have become less frequent. Global warming could explain this, says Mudelsee. Warmer winters would mean that fewer rivers become blocked with ice and burst their banks.

“Dumb places”

A separate study mapping the flood threat to home-owners in the UK found a rising trend, but blamed people, not climate change.

The team, led by Edmund Penning-Rowsell, at Middlesex University’s Flood Hazard Research Centre, mapped how factors such as climate change, the density of buildings and the quality of flood defences would affect flooding over the next century.

The researchers predict that 3.5 million people in the UK will be at high risk of floods by 2080, compared to 2.6 million now. Particularly dramatic was a map of the Thames Gateway, where the government plans to build 120,000 houses – the zone lies entirely on fluvial land and a tidal flood plain.

Ilan Kelman, from the Centre for Risk in the Built Environment at Cambridge University says: “If we build poor houses in dumb places, the flood risk increases, even if the hazard becomes less extreme.”

Journal reference: Nature (vol 425, p 166)