- An iron asteroid 20 metres (65.6ft) wide crashed into
the Arizona desert 49,000 years ago, creating a crater a mile wide and
174m (570ft) deep.
-
- The blast sent 175 million tons of rock flying into the
air and whipped up winds of 1,000km (621 miles) per hour.
-
- The effects on life in the region were devastating -
but what impact would a similar blast have on a modern city such as London?
-
- Scientists in the US have created a website to help us
assess the risks.
-
- According to researchers at the University of Arizona's
Lunar and Planetary Laboratory, a relatively modest sized asteroid of 45m
(148ft) in diameter hits the Earth approximately every 1,000 years.
-
- So what would happen if the next one were to land in
central London? How far would the devastation reach and how much time would
those living and working in the city have to grab their bags and run?
-
- To help assess the risks, University of Arizona researchers
have created a website to help predict the effects of different types of
asteroids and meteors would have if they hit different places on the planet.
-
- Gigantic fireball sets trees alight
-
- To use the site, you have to have an idea of what type
of object you are expecting to hit the Earth, where it will hit and at
what kind of speed and angle.
-
- Simply type in your distance from the predicted impact
point and the Earth Effects Impact Programme will tell you if you should
expect to be buried under a pile of debris, known as ejecta, while trees
are flattened for miles around or whether the effects will be limited to
loud noises and rocking cars.
-
- The site includes descriptions of the effects of different
types of impacts, including how much thermal radiation is needed to ignite
grass and how far away from the impact humans would suffer second or third-degree
burns.
-
- Planetary scientist Jay Melosh, who helped develop the
site, said: "The website is valuable for scientists because they don't
have to spend time digging up equations and data needed to calculate the
effects.
-
- "Similarly, it makes the information available to
reporters and other non-scientists who don't know how to make the calculations."
-
- The Arizona asteroid, thought to have been made of iron,
hit the Earth at a 90% angle at a speed of 20km (12.4 miles) per second.
-
- Inserting these figures into the online blast calculator
for a slightly bigger iron asteroid of 45m (148ft) wide reveals devastating
results should such an object hurtle into central London, landing say,
at Oxford Circus.
-
- An enormous crater 2.91km (1.81 miles) wide would spread
across what had been Oxford Street, Bond Street, Regent Street and Marble
Arch, wiping out much of Soho and Mayfair and sending hundreds of tons
of rock hurtling into the air.
-
- The immediate area would be vaporised instantly - the
shoppers and officer workers thronging the streets would not stand a chance.
-
- Rock thrown up by the blast would shower over an area
of several square miles around the crater like bombs, smashing through
the roofs of embassy buildings in Belgravia and skyscrapers in the City
of London.
-
- Just 0.04 seconds after the blast, a gigantic fireball,
0.8km (0.5 miles) across would appear, igniting trees, grass, paper and
clothing, with thermal radiation causing extensive third degree burns in
anyone unlucky enough to be caught within 1km of the blast .
-
- A fraction of a second later, shockwaves from the blast
would reach 5.4 on the Richter Scale, rocking cars up to 1km away, moving
furniture, cracking walls and making the ground unstable to walk on. Widespread
panic would likely ensue, with those who were able to running out of their
houses into the streets.
-
- Seismic shocks felt 60 miles away
-
- The shockwaves would gradually spread out from the impact
zone, reaching the London outskirts and the M25 about a second later.
-
- Finally, 3.3 seconds after the impact, winds reaching
4,007km (2489.7miles) per hour will rush through the city, at an ear-piercing
128 decibels, causing buildings and bridges to collapse, steel-framed office
blocks to buckle and blowing down 90% of the trees.
-
- Seismic shocks would reach the M25 after about four seconds,
rocking the ground, making it hard to stand up, church bells would ring
and furniture would be overturned.
-
- Even this far from the impact point, the fireball would
be visible, cars and lorries would be destroyed, glass would be shattered
and trees blown down and stripped of leaves by winds of 136km (84.6 miles)
per hour.
-
- The fireball following the impact would still be visible
by people almost 100km (60 miles) away in Sussex, Essex or Hertfordshire,
though the effects here would be milder.
-
- Although cars may still be rocked by seismic shaking
19 seconds after the blast, the winds will reach only 23km (14.4 miles)
per hour and will be no louder than heavy traffic noise.
-
- © BBC MMIV http://news.bbc.co.uk/2/hi/science/nature/3622183.stm
|
