Barringer Crater
Perhaps one of the most visible signs of the immense force created by a meteor impact is the Barringer Crater in Arizona. The huge hole in the land was made by a relatively small piece of rock travelling at colossal speed.
Dr Matthew Genge
The lesson of Tunguska helps explain why, in Chelyabinsk, there is so much damage yet very little meteor to be found.
Dr Matthew Genge “Really it’s a balance between the size of the object, its speed into the atmosphere and critically, the altitude at which it explodes. Too high, the shock wave has little effect on the ground. If the object is large or low to the ground the shock wave is devastating.”
Dr Marek Kukula “Actually seeing it in real life, brings home to you the energy that these things carry and even though it exploded tens of kilometres up in the air. The force of the explosion, the shock wave was able to damage buildings across a huge area and injure people. And that was quite a shocking thing to see.”
Professor Iain Stewart “The destructive power of an air blast is immense, but in a way the people of Chelyabinsk are lucky because out there in the cosmos is a different kind of asteroid one that poses an even greater threat. I’ve seen the evidence of what one of those can do, the damage that it leaves behind and what you realise is that Earth’s own destructive forces: great earthquakes and volcanic eruptions, seem trivial in comparison.”
This is Barringer Crater, Arizona. The 50,000-year-old remnant of a massive meteor impact.
Dr Marek Kukula
This place really gives you a sense of the destructive power of incoming meteorites. The blast here would have vaporised a city larger than London, but the lump of rock that did it measured at barely 50 metres across. Down on the ground, the scale of the impact is even more breathtaking. The creator is more than a kilometres across and nearly 200 metres deep.
The forces here were enormous. The impact turned this solid rock into this pulverised mush, it just bursts out in your hand. They started out as the same kind of rock. The meteor that struck here, and created the Barringer Crater, was about the same size as the one that flattened Tunguska, but there is a critical difference.
At the Barringer Crater the meteor didn’t explode in the atmosphere it struck the ground. So, this is just a fragment of the true devastation unleashed here.
Fortunately, to understand why ground strikes are so destructive we don’t have to wait for another Barringer to happen. Because today we can simulate this kind of impact. And that’s thanks to the research of Professor Pete Schultz and one very special piece of equipment.
Professor Peter Schultz
Pete Schultz “So, this was serial number 1. It was built during the Apollo time and they thought there would be several more made. But, this is the first one and the last. And, it’s the only one like it in the world.”
This is NASA’s vertical gun range it was built to study how impacts affected the moon, as astronauts prepared to make the first lunar landing. Today Prof. Peter Schultz uses it to model precisely the dynamics of an asteroid impact.
Pete Schultz “We know that these asteroid impacts are bad but we want to understand, really, how bad .”
Pete uses the NASA gun to fire projectiles at very high speed to simulate an asteroid hitting the Earth.
Pete Schultz “So for this experiment we’re going to fire this tiny quarter inch aluminium sphere at around 5 km/s and we will see what kind of crater it produces.”
The target it will hit is made of sand.
Pete Schultz “We use sand because it records the shock affects very clearly.”
Outside of the impact chamber are super-high-speed cameras that film at up to 1 million frames per second capturing every detail of the impact.
Peter Schultz “Perfect, now we’re seeing the fireball come in. It’s brighter than the sun and then Kapow it hits the surface. This whole region, down range would have been incinerated. It would have been incinerated just by this plasma, this exploding vapour plume engulfing everything. There would have been winds that would have been going so fast that they could pick up houses and spread them hundreds of kilometres away. This would have been Armageddon. Experiments like this reveal several important things . one is that it’s not just the impact, it’s all that vapour plume that runs down range. You can see areas here where there was so much wind that it carved out pieces of this landscape. So, what these experiments help us do is allow us to witness the event, see it in real time and try to understand the processes that are going on. It is really complex but we have to see it to understand it.”
So asteroid impacts release a trail of destruction far greater than suggested by the footprint of the Barringer crater alone. Comparing the effects of an air-burst with a ground strike seems that Chelyabinsk got away lightly.
It’s estimated that the largest piece to hit the ground weighed 500 kg, a fraction of the asteroid’s original mass of 7,000 tonnes.
Dr Natalie Starkey “Now, if a piece of rock that big had hit that area of Russia. It would have produced a huge impact crater.”
Dr Hugh Lewis
Dr Hugh Lewis “Then that kinetic energy was then delivered into the ground and we see things like seismic shock, so people would feel earthquakes on the ground, so the fact that it was an air burst limited the consequences for the people on the ground. So, yes still quite dramatic. Still, obviously, causing injuries but, it could have been a lot worse had it survived down to the ground.”
Ground strikes are amongst the most destructive natural hazards we know. When viewed from space Earth’s encounters with giant asteroids, in its deep history, are revealed. And there is evidence from our planet’s past of a really devastating meteor strike that decisively altered the course of life on Earth.
Today, millions of years after the impact, the evidence of that crator is well hidden. This is a gateway to the cenotes. The unique cave system of Mexico’s Yucatán Peninsula.
This cave may be stunning but it provides the evidence for one of the worlds greatest catastrophes in the Earth’s history. There is actually much more to this amazing cavern than first meets the eye. But, to understand the scale of what happened here, you have to go deeper still - underwater.
The Cenotes
Descending into the depths of the cenote is like entering into a new world. Fewer people have visited some of these drowned caverns than the surface of the moon. As divers have explored further we have discovered that the cenotes are actually part of the huge complex of tunnels and caves. In fact, when you look from above, you can see there are cenotes scattered across hundreds of kilometres.
And when they are mapped, it becomes apparent they follow a distinctly circular course through the jungle. They mark out the rim of a giant crater. Scientific instruments show the structure of the underlying rock has been deformed, revealing the boundaries of a colossal meteorite impact crater.
65 million years ago this was the site of one of the most catastrophic impacts in Earth’s history. What became known as the Chicxulub meteorite landed here, and that triggered the extinction of the dinosaurs.
The meteorite was 15 km across. Enough to cause utter devastation across the whole planet. It exploded with the force of 100 million, million tonnes of TNT. The blast sent a vast plume of vaporised rock out into space. A crater was punched 30 km into the Earth’s crust. It was above this rim of weakened rock that the cenotes formed, millions of years later. The blast would have been ferocious.
But, it was what happened next that made the impact a global catastrophe. The blast plume that shot into space fell back to Earth. Billions of molten particles superheated the air to the temperature of hundreds of degrees. Fires swept the planet, choking the atmosphere with suit and dust. The dinosaurs and most other creatures were doomed.
That discovery back in the 1980s about what happened at Chicxulub changed everything. Up until then we thought that the Earth changed only through grindingly slow processes. But, now we knew that it was also sudden violent catastrophes that made the Earth the way it was. Of course, what that meant was that something like this could happen again, at any moment!
External Links
Barringer Crater, formerly Canyon Diablo Crater - Wikipedia Page
Further Reading
[amazon asin=0600200167&template=add to cart] Meteor - Edmund H. North and Franklin Coen
[amazon asin=0387765735&template=add to cart] The Tunguska Mystery - Vladimir Rubtsov
