Another unusual test comes from Peter Clift. In another paper delivered at the Fall 2004 meeting of the American Geophysical Union, Clift explained that he is trying to test the plume theory by examining fossils in seabed sediments laid down on top of those undersea plateaus called LIPs.
If large igneous provinces really are created by plume heads, the eruptions that formed them should not only have flooded the seabed with lava, but also have uplifted it. All eruptions create uplift, but plume heads should produce unusually large amounts.
When an eruption ends, the seabed slowly subsides. Again, this is normal, but if the uplift was unusually large, the rate of subsidence should be unusually rapid.
Clift realized that he could test this using a class of fossils called foraminifera. These single-celled creatures have hard shells, which accumulate in marine deposits. Different types live at different depths, which means that cataloging the foraminifera in a sediment tells you the depth of the water in which it was formed. Doing this for each sediment layer gives you the LIP's initial depth and its rate of subsidence.
Unfortunately, the results are mixed. Some LIPs are subsiding quickly, as expected. Others are subsiding more quickly than the average ocean crust, but not quickly enough for the plume model. And still others are subsiding more slowly than the surrounding crust.
One explanation is that LIPs (or at least, some of them) don't represent plume heads. Another is that when a plume head hits the underside of the crust, part of it may stick there, crystallizing into buoyant rock (such as granite) that keeps the LIP from subsiding as expected.
Support for the latter interpretation comes from Yi-Gang Xu of the Chinese Academy of Sciences, who studied his country's Emeishan region, conventionally believed to have been created by a plume head.
Like Clift, Xu was looking for signs of ancient uplift, but since he was working on land, he couldn't rely on foraminifera. Instead, he hypothesized that the rising plume should have elevated the landscape in a dome-shaped formation before the lava broke through. Since plumes move slowly, this pre-eruption uplift should have persisted long enough to have been subject to erosion—and the higher the dome's center was, the more it should have eroded.
Luckily for Xu, the lava emerged through a layer of limestone that was probably uniformly thick. By measuring how much of the limestone remains in various places, it's therefore possible to map the areas of highest erosion, creating a crude contour map of the uplift. (Erosion would have continued after the eruption, but at that point, it would have been the lava, not the limestone, that was eroding.)
What Xu found precisely matched his hypothesis: the limestone is thinner at the center of the volcanic region than at the edges in a nice bull's-eye pattern that strongly indicates a central uplift. In addition, trace element analysis of the basalt itself indicated that the center was hotter than the edges—also consistent with a plume. Finally, seismic tomography indicates that the crust is 55 to 64 km thick in the volcanic zone's center, but only 35 km thick at its edges. This, Xu believes, reveals the remnants of the plume head sticking to the bottom of the crust—exactly what Clift needed to explain his anomalous LIPs.
* * * *
Propagating Cracks
All of this research indicates that the plume theory is likely to withstand its challengers. It's hard to imagine that Hawaii isn't the result of something at least very much akin to a hotspot. The same would seem to apply to Olympus Mons.[14] At the same time, it is likely that when the dust settles, the theory will have had its wings clipped—possibly severely—and that many regions once viewed as hotspots (perhaps including Iceland) will prove to be something else.
Foulger's main complaint is that when everyone jumped on the plume bandwagon in the ‘70s and ‘80s, nobody really looked into alternative theories. Instead, the “great love affair with plumes” encouraged geologists to try to fit everything and anything into the theory, without asking whether there might be simpler explanations.
Foulger and her colleagues offer several alternatives that deserve to be studied in greater detail. One is that hotspot volcanism originates from exotic accidents of plate tectonics in which large chunks of seabed break off mid-plate and are drawn deep into the mantle. She also suggests that you could get flood basalts such as the Siberian Traps from “lithospheric delamination,” which would occur if the bottom layer of the crust somehow broke free and allowed hot mantle rocks to fill the void.
Another theory is that the features we see as plume tracks might be created by “propagating cracks” that began at one point in the seafloor (or continent) and gradually unzipped over the course of millions of years.
James H. Natland of the University of Miami points out that the Pacific Ocean has 10,000 seamounts, most of which nobody has attempted to link to hotspots. Many of these can't possibly be the work of plumes because they lie in long ridges that erupted more or less simultaneously along their entire length.
Natland's belief is that when the Pacific Plate was younger (and smaller) it was subject to stresses that produced fissures that cracked over long distances, all at once. Later, different stresses began producing sequential eruptions that look like hotspots but aren't.
To spur further research, Foulger has helped create a website on mantle plumes: www.mantlepumes.org. Some of the material is technical, but much is accessible to the average reader.
From a science-fictional perspective, the hotspot controversy is a fascinating example of the scientific process at work. It could also make the subject for a truly ghastly movie. Imagine what would happen if a previously undetected plume head rose beneath Washington, D.C., or if terrorists found a way to create a new hotspot. As the plume rose, the entire East Coast would bulge upward. Port cities would become plateaus. Rocks would crack and lava would inundate everything.
It would be the greatest disaster movie of all time! Of course, in reality, you'd get thousands of years of warning (that “new” plume in the Coral Sea isn't going to erupt anytime soon), but in the realm of bad science fiction movies, when was the last time anyone worried much about minor technicalities like a few thousand years?
Meanwhile, actual scientists continue to wonder whether plumes are messengers from the Earth's core. If they are, real science fiction can raise the question of what they're trying to tell us.
So far we have no idea, but the one thing I'm sure of is that if I were investigating a planet like Mars, I'd love to have samples from Olympus Mons. And what an adventure it would be to climb it to collect them!
Copyright 2006 Richard A. Lovett
* * * *
[1 Ptolemy was the ancient astronomer who developed a complex Solar System model with the planets revolving around the Earth. Ether was the invisible medium through which light waves supposedly propagated, like sound waves in air.]
[2 Okay, so I'm being cute. Some folks would say that the biosphere is a thin layer, distinct from the crust. But crustal geology and biology are strongly enough linked (think about the processes that form coal, oil, and limestone, for example) that this is an artificial distinction.]
[3 As we'll discuss later, our primary way of “looking” at the mantle is by the way it conducts seismic waves from earthquakes. To the extent that seismic waves reflect off the boundary rather than passing through it, all you see is the boundary.]
[4 There are old science fiction stories that feature deep subway-like tunnels through the mantle. From a physics point of view, these stories are fun because, if the tunnel carries a hard enough vacuum and the train has low enough friction, it's a quick, low-energy way to go thousands of miles: you simply let the train roll down the hole, gathering speed as it goes, until it reaches the bottom and is carried back uphill by its momentum. From a geophysics point of view, though, the concept is nonsense. Not only does it require a monstrous air-conditioner to keep from melting the train, but the tunnel walls need to resist pressures that make those in the deepest ocean trenches seem trivial. If you accomplish all of that,
you still have to deal with those pesky mantle currents, which are going to throw the tunnel out of alignment. Of course, those old stories were written back before anyone had dreamed of mantle currents, so the authors can be forgiven for overlooking them.]
[5 Anderson's list, with latitudes and longitudes, is at www.mantleplumes.org/CompleateHotspot.html.]
[6 At least one recent model indicates that the mushroom shape may not always occur, but that doesn't mean it isn't common.]
[7 Basalt is a common volcanic rock. It's black, dense, and can flow for great distances.]
[8 In volcanology, a “trap” is a type of lava.]
[9 She appears to have done a good job with the calculation because I've never heard anyone argue with the result.]
[10 The similarity comes from the fact that both words use the Greek root “petra,"]
[11 “Finite-frequency tomography reveals a variety of plumes in the mantle,” Science, 303, 338-343, January 16, 2004.]
[12 Even non-experts weren't too thrilled. Several of my friends are science writers for major newspapers, and the talk in the pressroom was that you could see anything you wanted in the Science data. It's one thing to write about such things for a sophisticated Analog audience; it's another to try to condense it to 600 words for a general audience. There's a reason you never read about this over your morning cup of java!]
[13 Or, as mentioned earlier, maybe the imaging simply cannot trace them through]
[14 Many scientists also think there are hotspots on Venus, but if that's the case, the process works very differently than on Mars. Rather than forming recognizable volcanoes, the Venusian features are flat, circular plains that look suspiciously like impact craters. The only real problem with instantly classifying them as impact craters is that they're big—which means that they must date from the dawn of the Solar System. They're also very sharp and pristine, which means that if they really are that old, the surface of Venus must be nearly as erosion-free as the Moon's: a conclusion that many planetary scientists reject. For more on this topic, go to www.mantleplumes.org and click the link labeled “Planetary.” This site also presents alternatives to the plume hypothesis for the formation of Olympus Mons.]
[Back to Table of Contents]
* * *
TOTAL LOSS
by JAMES HOSEK
Are you sure it can't come to this?
Pain was just beginning to seep through the medication. It was enough to bring Gary Carter back to consciousness. His eyes squinted against the bright lights and the realization that he was in a hospital emergency room brought back his memory. There had been an accident.
He remembered the yellow Ford Escape turning left right in front of him. He remembered seeing a look of panic on the woman's face, cell phone glued to the side of her head, as she saw Gary's ‘89 Geo Metro approaching. For some insane reason she stepped on her brakes! If she had just completed the turn she would have cleared the intersection and Gary would have missed her. As it was he had no choice but to slam on his own brakes. Wheels locked, he skidded across the drizzle-covered pavement into the passenger side of the SUV. He remembered the woman's scream over the crunching of metal.
Then he must have blacked out because the next thing he remembered was the paramedics and some firemen working to extract him from his car. Speckles of his own blood dotted the steering wheel and dashboard; the front end of his subcompact was crushed like a beer can on a cowboy's forehead at the end of happy hour.
He vaguely remembered the paramedics telling him his legs were going to hurt before he blacked out again. Now as he looked down at his legs it was obvious he had broken them both.
“You're awake, Mr. Carter,” said a cheerful voice. Gary turned to see a young, dark-haired, unshaven face looking at his. A laminated ID card hanging around his neck over his green scrubs read “Dr. Morgan.” He was looking at a flat screen monitor near the bed, on which some broken white sticks were visible on a black background. It took Gary a moment to realize they were his legs.
“That's me?” he asked.
“Afraid so. Still, I've seen worse. The surgeons should be able to fix you up. We've got you in some splints now to keep the bones from moving around, but once we get you to an OR they'll put on a few plates, some screws. Bad news is you'll never be able to clear airport security again.” Morgan laughed but stopped short as he realized Gary wasn't appreciating the joke. “I'll, uh, check what's keeping the surgery consult,” said Morgan. He smiled briefly before disappearing behind a curtain.
Gary leaned back and tried to take a deep breath. Soreness was beginning to creep into places he hadn't realized he'd hurt until just now. Kate was going to be pissed. Not only about the accident, but his wife had wanted him to trade in his old Metro for years. She was always worried that if he were in an accident he would get killed. He was in for a well deserved “I told you so."
“Mr. Carter?” asked a nervous voice. Gary was expecting another green scrubbed ER person but instead a small man was peering around the hanging curtain. The man's eyes darted around the hospital bed taking in the IVs, patient monitor, splints, and the radiographs still displayed on the video monitor. His manner reminded Gary of a scared ferret, unsure if it was safe to cross the room lest a cat intercept him from behind a potted plant.
“I'm him,” answered Gary, “At least what's left of him."
“Oh my, this is quite out of the ordinary, I'm afraid,” prefaced the ferret.
“And you are?” led Gary trying to figure out what this was all about.
“Ah, yes.” He reached inside his jacket pocket and pulled out a card. He went to hand it to Gary. Unfortunately Gary's right hand was strapped to a board to keep his IV from pulling out and his left was covered with a large padded bandage with a pulse oximeter probe clipped over his middle finger. The ferret, undaunted, slipped the card between two fingers of Gary's right hand. “Bernard Crawford,” he said, “Chicago Casualty. Your insurance company."
“Wow,” realized Gary. “This is out of the ordinary. I haven't even called our insurance agent yet. You guys certainly give prompt service."
“Actually, the hospital called. I was in the building for another client and, uh, thought I'd take care of this right away, but I see you're, uh, still, uh, awake."
“Well, I didn't hit my head that hard and despite the pain medication, my legs are throbbing just enough to remind me what happened."
“Well, Mr. Carter,” Crawford fidgeted, keeping his eyes off Gary, “I regret to inform you that based on the situation and damage incurred, we are determining your case to be a total loss. I'm very sorry."
“Well,” realized Gary, “I pretty much figured that after seeing the damage myself. But even the police office agreed it was the other woman's fault."
“Well, I don't deal with fault, Mr. Carter—just the numbers, you see."
“Of course,” said Gary. “I don't think I'll be driving for quite some time, so it might be better to settle up after I've had some time to recover. I know it was an older car, but it must be worth something."
“Car?” repeated Crawford, confusion creasing his forehead, which was starting to bead with sweat.
“Yes, my Geo. You said it was a total loss. I assume I might still get a thousand or so out of it. It was in pretty good shape despite the mileage."
“Oh, no, Mr. Carter. You have this all wrong. I'm from Chicago Casualty. I represent your major medical carrier. I'm the adjustor that has been assigned to assess your injuries and make recommendations regarding your care."
“I'm confused,” said Gary. He tried to adjust his position in the bed and get a better look at the business card stuck between his fingers. The movement intensified the pain in his legs. He waited for the wave to pass and noticed Mr. Crawford becoming more uncomfortable, his fingers ringing the handle of his briefcase. “You did say that my case was a total loss?"
“Yes, I'm afraid so. I've been over the estimates three times. I'm afraid I can't justify the needed
surgery and rehabilitation based on your life expectancy and the current value of your body parts."
Gary widened his eyes and stared at the insurance man.
Crawford continued. “We will cover five days of minimal hospitalization with adequate pain medication to keep you comfortable, but after that time, I'm afraid we must insist that you, well, stop receiving medical care and we be allowed to salvage the body for any useful parts to recoup our expenditures to this point."
“Expenditures?” asked Gary, “All they did was put in an IV and wrap my legs with these splints. This must be a joke. Is there a hidden camera around here?"
“No. No camera. But the expenses so far have been considerable, Mr. Carter,” began Crawford. He set his briefcase on the side of the bed and opened the clasp. He pulled out a small tablet PC and tapped on the screen a few times. “Here it is,” he announced with a smile on his face. He seemed much more comfortable now that he had some numbers to look at, rather than Gary's confused face.
Gary blinked a few times. This must all be a hallucination from the pain medication. This couldn't be happening. Insurance companies didn't treat people like cars and salvage them for parts. They had to pay for his care. That was why he and Kate had paid premiums every month. They had to fix him up. They were insured through Kate's work since Gary had his one-man computer programming business. Her company had changed insurance providers just a few months ago because of increasing costs, but that was nothing unusual. It had happened every few years. Sometimes it meant they had to change doctors, but this situation was insane.
They had gotten a packet of materials when the new insurance went into effect, but Gary had just filed it, never bothering to read the pages and pages of coverages and exclusions and fine print. He just assumed like every other health insurance policy, it would allow them to get whatever coverage they needed. He had heard of people being denied coverage for experimental treatments, but this was a couple of broken legs and some cuts.
Analog SFF, July-August 2006 Page 8
