Mt
and the third
10 6 Mt
. “I examined three scenarios which straddle the likely energy range. I’m calling them Baby Bear, Mummy Bear and Daddy Bear. As you see Baby Bear is ten thousand megatons, Mummy Bear a hundred thousand and Big Daddy is a million.
“First I had a look at Baby Bear, deep ocean impact. I had the idea that maybe the aggressors—the Russians?—might want to take out the UK or Japan while they were about it. Anyway, the Atlantic and the Pacific are big, easy targets. Okay. So half a minute into impact we have a ring of water three or four hundred metres high. Wave amplitude falls as it moves out but you’re still looking at a fifteen-metre wave a thousand kilometres from the impact site.”
“In the open sea?” Shafer asked.
“In the open sea. Tsunamis are long-range, because the ocean is a surface and specific energy drops linearly with distance rather than inverse square. An earthquake in Chile in 1960 created ocean waves which travelled over ten thousand miles and killed a lot of people in Japan.”
“What was its wave height?” McNally asked, coming back from the window.
“In the open sea, twenty centimetres. The wavelength is hundreds of kilometres.”
“An eight-inch wave killed people?” McNally asked, bewildered.
Sacheverell winced. “No. When the wave runs into shallow water the same amount of energy is being carried by less and less water. So when it approaches a shoreline it rears up. The twenty-centimetre wave became a metre or two high. Killed a couple of hundred people, if you count the ones that just went missing.”
“So what’s the run-up factor on your fifteen-metre wave, Herb?” Shafer asked.
“Ten to forty, depending on the shoreline. If we say twenty, the wave is three hundred metres high when it hits land, assuming the impact was a thousand kilometres offshore.”
“The height of the Eiffel Tower,” Leclerc said. “How far inland would a wave like that travel?”
“Again it depends. Topography, roughness of surface. Flat agricultural land would flood for ten or twenty kilometres inland. When I say flood, I mean the wave is still two hundred metres high maybe five kilometres inshore.”
Webb said: “An Atlantic splash of that order would take out nearly all the major cities in Britain.” Although he was actually trying to visualize a half-mile tsunami roaring up Glen Etive.
“I don’t believe these figures,” Shafer said, without bothering to explain why.
“Europe is protected by a steep continental shelf,” Sacheverell informed Webb. “It reflects about three quarters of the energy back into the ocean.”
“Great,” Webb said. “Really great. Now I know that when I turn into Piccadilly the wave coming at me is only a hundred metres high.”
Noordhof went to the percolator and came back with a refill. “And if Baby Bear hits land?”
“Blast, heat and earthquake. The blast is a pressure pulse followed by a hot wind. The nuclear weapons people use an overpressure of four psi to define total devastation although there’s huge loss of life even at two, mainly from blizzards of flying glass in urban areas. Hit L. A. and you’ll blow theroofs off houses in San Diego. A Baby Bear on Philadelphia would rip people up from Baltimore in the south to New York in the north.”
“You could take out England from London to Newcastle,” Webb interrupted, still doing his patriotic bit.
“Who would want to zap your feeble little island?” Sacheverell asked. “I’ve taken the threshold for fire ignition to be about a kilowatt applied to a square inch for a second. It turns out you ignite everything in sight—tyres, grass, everything flammable. A hundred miles away, it’s like standing four inches from an electric fire for ninety seconds.”
“That must depend on whether the asteroid hits the ground or breaks up in the air,” said McNally.
“No. The heat comes from the hot wake trailing the fireball. Lastly, earthquake. I’ve taken
and the third
10 6 Mt
. “I examined three scenarios which straddle the likely energy range. I’m calling them Baby Bear, Mummy Bear and Daddy Bear. As you see Baby Bear is ten thousand megatons, Mummy Bear a hundred thousand and Big Daddy is a million.
“First I had a look at Baby Bear, deep ocean impact. I had the idea that maybe the aggressors—the Russians?—might want to take out the UK or Japan while they were about it. Anyway, the Atlantic and the Pacific are big, easy targets. Okay. So half a minute into impact we have a ring of water three or four hundred metres high. Wave amplitude falls as it moves out but you’re still looking at a fifteen-metre wave a thousand kilometres from the impact site.”
“In the open sea?” Shafer asked.
“In the open sea. Tsunamis are long-range, because the ocean is a surface and specific energy drops linearly with distance rather than inverse square. An earthquake in Chile in 1960 created ocean waves which travelled over ten thousand miles and killed a lot of people in Japan.”
“What was its wave height?” McNally asked, coming back from the window.
“In the open sea, twenty centimetres. The wavelength is hundreds of kilometres.”
“An eight-inch wave killed people?” McNally asked, bewildered.
Sacheverell winced. “No. When the wave runs into shallow water the same amount of energy is being carried by less and less water. So when it approaches a shoreline it rears up. The twenty-centimetre wave became a metre or two high. Killed a couple of hundred people, if you count the ones that just went missing.”
“So what’s the run-up factor on your fifteen-metre wave, Herb?” Shafer asked.
“Ten to forty, depending on the shoreline. If we say twenty, the wave is three hundred metres high when it hits land, assuming the impact was a thousand kilometres offshore.”
“The height of the Eiffel Tower,” Leclerc said. “How far inland would a wave like that travel?”
“Again it depends. Topography, roughness of surface. Flat agricultural land would flood for ten or twenty kilometres inland. When I say flood, I mean the wave is still two hundred metres high maybe five kilometres inshore.”
Webb said: “An Atlantic splash of that order would take out nearly all the major cities in Britain.” Although he was actually trying to visualize a half-mile tsunami roaring up Glen Etive.
“I don’t believe these figures,” Shafer said, without bothering to explain why.
“Europe is protected by a steep continental shelf,” Sacheverell informed Webb. “It reflects about three quarters of the energy back into the ocean.”
“Great,” Webb said. “Really great. Now I know that when I turn into Piccadilly the wave coming at me is only a hundred metres high.”
Noordhof went to the percolator and came back with a refill. “And if Baby Bear hits land?”
“Blast, heat and earthquake. The blast is a pressure pulse followed by a hot wind. The nuclear weapons people use an overpressure of four psi to define total devastation although there’s huge loss of life even at two, mainly from blizzards of flying glass in urban areas. Hit L. A. and you’ll blow theroofs off houses in San Diego. A Baby Bear on Philadelphia would rip people up from Baltimore in the south to New York in the north.”
“You could take out England from London to Newcastle,” Webb interrupted, still doing his patriotic bit.
“Who would want to zap your feeble little island?” Sacheverell asked. “I’ve taken the threshold for fire ignition to be about a kilowatt applied to a square inch for a second. It turns out you ignite everything in sight—tyres, grass, everything flammable. A hundred miles away, it’s like standing four inches from an electric fire for ninety seconds.”
“That must depend on whether the asteroid hits the ground or breaks up in the air,” said McNally.
“No. The heat comes from the hot wake trailing the fireball. Lastly, earthquake. I’ve taken
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