Archived Posts from this Category
Archived Posts from this Category
It’s silt, really. Pieces of mountains, ground down by the Cook Inlet glacier during the last ice age, and by the smaller glaciers that surround it now — washed up and down Cook Inlet with every tide. Along the Kenai Peninsula, it flows down from the layered bluffs in grey-brown trickles, fanning out into wet shiny patches that Katmai calls “cold lava.” Rounding the corner at Point Possession, the silt takes over the world.
It took over our gear. I pulled a grape sized chunk of compacted silt out of my shoe, which had gained half again its weight in clay-like paste. Both shoes finally burst out the sides, as the silt squeezed out all the space for my feet. Each time I blew up the sleeping pads, I could feel the grit between my teeth. It formed a fine gray dust that rained out of everything we owned — pouring from every drybag, shaking from every piece of clothing. It mixed with the layers of sunblock to form a dark grey makeup that eventually took fifteen minutes of scrubbing to remove from my face. Even now, after several days in Anchorage, I find little pockets of Turnagain buried deep within our stuff.
In Chikaloon Bay there was no beach, just mud flats extending up into marsh. We landed here, on mud-coated ice.
At high tide in Chickaloon Bay, the silt was so close we could hit it with our paddles — far from any visible shore. At low tide in Chickaloon Bay we wove through an endless maze of dunes and mudflats, first on foot, then in the rafts, as the rising tide turned dips into streams, rapidly erasing square miles of land. The silt followed us into Turnagain, where we leapt on it like a trampoline to demonstrate the liquefaction. Then skirted the cliffs on a thin edge of slippery mud to avoid the worst of the liquefaction.
An initially firm beach acquired a water-bed like consistency when we spent some time jumping up and down on it.
Liquefaction is quicksand. It’s quickly deposited silt, filling up a channel in the course of a tide, so unstable that it will turn to leg-sucking goo with a footstep. Someone died in it once, decades ago. Others have been rescued. It’s more easily avoided than many people realize, by staying on the high and dry edges. It’s more easily escaped than many people realize also, by floating your legs out rather than working them deeper in. We carried packrafts — inflated — which makes getting out of liquefied silt into a task as simple as leaning on the boat.
But, like many aspects of the wilderness, liquifying silt takes thought to deal with safely. So do tidal currents. And the presence of both things is what turns Turnagain Arm into a strange sort of no-man’s land — a trivial distance from hundreds of thousands of Anchorage residents, but almost never visited. It’s surrounded by more widely-accepted risks: A busy and deadly highway, avalanche-prone ski terrain, boat-flipping whitewater, bear-dense trails… Surfers visit Turnagain when the big bores come. But in the whole time we were there, we saw only one boat other than our two packrafts (and our friend Erik’s, when he was visiting us). So we had the tides to ourselves, riding up and down Turnagain on a conveyor belt that could move us up to five miles an hour.
Not the most scenic route, but we stuck to our plan to continue our human-powered route through the city.
That conveyor belt brought us to the Turnagain Arm trail, which brought us to Anchorage. In Kenai we were urban as well, but the experience there was one of beach-based couchsurfing, where each day we’d walk and paddle a few miles of shoreline, then scramble up the bluffs to someone’s house. We knew the highway was out there, but we never saw it. In Anchorage, on the other hand, our path has taken us right through the center of town. Sometimes on bike paths, and sometimes on sidewalks right beside streets roaring with four lanes of traffic, several cars zipping past us every second of our walk. And I guess I’m more countrified than I thought, because I simply cannot imagine where so many many people have to be so very very quickly all the time.
We didn’t have to walk through Anchorage. That was simply our own arbitrary rule. Traveling is often full of rules: The speed limits and traffic signs on a highway. The tickets and lines and security restrictions at an airport. The schedules and fares on a boat…
On an expedition, we get to make our own rules. Sometimes we don’t. We’ve done trips that include hitching rides on trucks, four-wheelers and skiffs. When we walked from Seattle to the Aleutian Islands, we made ourselves a rule so strict that we could not enter any form of motorized transportation for an entire year. This time, we’re keeping our steps together — creating a continuous human-powered line around Cook Inlet. We allow ourselves to jump away from that line, as long as we return to it again leaving no gap. Often we’ve caught a ride to visit someone off the path, then rode back to where we left it.
Why have rules? This is not a race, and there is no one keeping record books. But the rules are the boundaries that shape the experience. Keeping a continuous line stops us from skipping over the things that seem hard (like the mudflats of Chickaloon Bay), and the things that seem worthlessly easy (like the strip malls of Anchorage). If I wanted to go backpacking for a few days, I’d never choose either of those places. But the trip is richer for seeing both of them. Jumping away from the line adds something too — the only way to visit people more than a mile or two out of the way, with a kid for whom a mile or two is still a big part of the day (he can walk up to 7.5 miles per day, if it’s easy terrain and he’s in the mood).
In the very short term, we’ll be in Anchorage until Tuesday, when you can catch us on Talk of Alaska.
Then we paddle across Knik Arm, where we turn a geographical corner that separates two very different halves of the trip. The mudflats will continue. The highways and cities will not. I hope the snow won’t either.
Finally, a few photos taken over the past month…
Travis has read Erin’s book. He was working on his transmission when we walked by, and recognized us – the packraft paraphernalia plus kids were the giveaway I think. He walked with us for a little while in south Anchorage.
2012 was a busy year for scientists working on issues related to Pebble Mine. I’m one of those scientists. I received my PhD studying tsunamis and learned a bit about earthquakes along the way. Given that PLP hopes to build giant dams that need to stand forever, earthquakes are a fairly important question. Between completing my own geologic fieldwork and critiquing the work of PLP and the EPA, there’s been plenty to keep me busy – so much so that I neglected to post anything on our blog about it all year, despite a number of interesting developments.
If developed, Pebble Mine would tap the largest gold deposit on the planet, and the copper in that deposit would likely be worth even more than all that gold. Its footprint would sit on the headwaters of some of the world’s greatest salmon rivers. It would leave behind towering tailings dams that would pose catastrophic risk for millennia, long after the boom of the mine has been forgotten.
The mine company’s perspective is simple and hasn’t changed since at least 2006: The threat of earthquakes is low because there are no active faults nearby.
This optimistic view of seismic hazard is based on ignorance. Existing scientific studies tell us almost nothing about faults in the area.
I wrote a letter of concern in early 2008 to Alaska’s Department of Natural Resources (DNR) about the uncertainty regarding seismic hazard near Pebble.
More importantly, I’ve tried to do something about that uncertainty – trying to locate and characterize earthquake faults in the area myself. In the years since, I have gone into the field to gather data as often as our meager funding would allow, frequently with my colleague Andrew Mattox. As 2012 dawned, we had a few promising leads.
In February 2012, PLP released a whopping 30,800-page “Environmental Baseline Document” (EBD) that included data and analyses from $120 million in scientific studies in the mine area. This document was meant to describe current conditions in the region around the mine – conditions that would both affect and be affected by mine development.
The seismic hazard analysis was only 7 pages long.
I had had high expectations for this document. In earlier statements, PLP hinted at carefully collected geophysical data that might reveal the location of the Lake Clark Fault, a fault that is of particular interest since it’s large and goes somewhere in the vicinity of the mine. It turned out that not one bit of new data was presented in the chapter’s four pages of text plus three figures.
The analysis also used scientific reasoning that was often bizarre or ridiculous. The rocks near the mine site are too strong for faults to break them? Faults follow glaciers? Both of these assertions can be easily disproven by example.
“The seismic hazard assessment presented in Pebble Limited Partnership’s Environmental Baseline Document is flawed. It draws strong, optimistic conclusions from weak evidence, and relies on geologic arguments inconsistent with observed evidence. It misrepresents existing research and fails to use key data sets that PLP has in-hand to inform the analysis. A major fault, the Lake Clark Fault, passes near the Pebble prospect. No published studies establish this fault’s location or seismic activity near the prospect, and the hazard assessment presents no effort to positively determine its location. The hazard assessment fails to consider minor faults or induced seismicity. Without further study, the hazard posed by earthquakes is impossible to determine. “
Hig presenting his critique of the EBD at a scientific conference.
It was satisfying to holler, “Your Science is WEAK!” but it left me wondering why it was so weak.
PLP must either be strategically holding back information, or else it lacks the expertise to do a real seismic hazard assessment. Put crudely: Either PLP is lying, or it’s incompetent.
In February 2011, Northern Dynasty, half-owner of PLP, released a report announcing, “The location of [the Lake Clark] fault has been identified as part of a geophysical survey of the region.”
Between this report (which lacked both data and analysis) and an email conversation I had with Ken Taylor, PLP’s former “VP for the Environment,” it appears that this identification was based on studies that PLP had conducted. Yet, the EBD omits this work, which can hardly be an accident. Why rely on old assumptions about the location of the Lake Clark Fault when your own scientists have located it using geophysical data?
Maybe PLP didn’t like the results of its earlier work, so instead it published a false analysis that told a rosier story.
Perhaps the poor quality of PLP’s seismic hazard assessment is unintentional. The bizarre assertions, lack of new scientific studies, and misinterpretation of existing literature are mistakes. Graham Greenaway, the main author of the seismic hazard assessment, isn’t even a geologist, so it’s understandable that he might not see the weaknesses. It’s frustrating to me that PLP has stood by its analysis despite my work to clearly lay out the problems (I’ve shared this with PLP on a number of occasions), but what more can you do?
Isolated chunks of sediment floated in a soup of sand, silt, and water presumably liquefied by shaking.
I suppose one thing I could do is try to figure out what’s going on myself. Andrew and I flew out to Lake Iliamna last June in search of evidence of earthquakes. We aimed to check out a couple of leads: A possible telltale sag in ancient shorelines above the lake suggesting a buried fault, and swirled sediment resulting from liquefaction, a common effect of strong shaking from earthquakes.
We hit a geologist’s jackpot: We found where an ancient peat bog suddenly burst open, a great fountain of liquefied sand pouring out to cover the ground. This sort of dramatic liquefaction is rare, and nearly always occurs during strong earthquakes. Examples of this phenomenon can be seen in eyewitness videos during earthquakes in Japan and Christchurch, NZ.
In combination with evidence that we found of tectonic deformation in the old shorelines, this liquefaction is decent evidence for past earthquakes. For more details, you can read our preliminary report.
Having publicized our work, I’d like to think that our job here is done. I have contacted scientists working for PLP and regulatory agencies, and ideally they will follow up on our findings, possibly confirming that the Lake Clark Fault is indeed active. Such a conclusion might warrant expensive changes to tailings dam engineering or abandonment of mine plans and prompt these organizations to inform local communities about risks such as strong shaking and lake tsunamis.
Honestly I don’t really understand how scientific results inform regulatory decisions, but what I’ve seen so far does not make me confident. It’s very easy to fail to find evidence. The mine company has financial incentives to overlook evidence of earthquake risk, just as I have financial motivation beyond merely curiosity to find that evidence – my funding comes from groups opposed to mine development. And regulators, ideally the impartial party here, have tight budgets and a broad mandate, thus little time to focus deeply on a difficult scientific problem like this. Tackling this problem would put government scientists into a political minefield that they may not wish to enter.
This year we’ve seen “the system” attempting to face the scientific challenges presented by the massive scale of Pebble Mine. The EPA, on the invitation of villages in the region, conducted a detailed “Watershed Assessment,” which is still under peer review. PLP criticized the EPA’s effort as premature and misguided, and pushed its own process, the PLP-funded Keystone Center dialogue. This in turn has been criticized for its biased exclusion of non-PLP science, among other things. Though I submitted my own work on seismic hazards, it was not considered even during the panel specifically on this topic. These efforts represent attempts to assemble expert assessments and critique PLP‘s science, but we’re a long way off from seeing concrete results from either. Though I’ve repeatedly pointed out unequivocal flaws in PLP‘s seismic hazard assessment, there was no acknowledgment of these issues as of the Keystone meeting in early October. If you want to see my testimony, you can go here, and skip to 17 minutes, 40 seconds.
So I’m going to stick to it. I have more data analysis, and a paper to write and submit for peer review. And hopefully I’ll have funding to get back into the field this summer.
Often it seems like marketers and politicians control the big issues. But I do believe that objective truth has a small edge in the game. It may not guarantee success, but it’s a nice ally to have. I think science is our best tool to uncover this objective truth.
This is the first of a series of posts from our adventure within 1/4 mile of home.
This is the first of a series of posts from our adventure within 1/4 mile of home.
The transformation was nearly instant. From whining over the exact proper amount of jam and milk in his oatmeal, to slipping bare feet into rubber boots (one bumblebee striped, one black, both on the wrong feet), racing out the door at dad’s promise to measure something with the measuring tape. Hig followed, while I pulled a squawking and barefoot Lituya from where she balanced on the doorframe, stuffing her in the duct-taped yellow rain suit that had borne all the abuse of Malaspina Glacier and a pair of black neoprene booties that had suffered the same. I was still in my nightgown. Soon we were all outside, and Katmai squeaking in high-pitched excitement each time he found a currant bush, Hig noting down leaf sizes on a clipboard, Lituya struggling to catch up as they flitted from bush to bush. It was just what we envisioned. For about 15 minutes.
The currants are one of the first plants to leaf out in the spring, and of course the largest leaves are right where we know the snow always melts out first. But before we could notice anything more profound, the kids were onto another idea.
How to stay near home but not AT home? Learn something new about a place we see all the time, rather than falling into regular patterns of work and chores? And do it at a level that can interest people from age 1 to 35? Backyard adventures allow us to slide into a relaxation impossible to achieve with the logistics, gear weight, and distances of an expedition. But juggling the desires of four, and hanging onto visions of learning and adventure while surrounded by all of your toys (adults and kids) requires a complicated balance.
Hig dumps a bucket of muddy water from a quickly-filling hole in the marsh, as he digs down to learn more about its geologic history.
A stone’s throw away and ten thousand years ago, a small patch of sloping ground stood clean and barren in the wake of retreating glaciers. Water streamed over the relatively impermeable surface of silty mud ground fine by the ice of the Kachemak Glacier. A few straggling plants popped up, adding their meager nutrients to the barren ground. When these plants died, they lay on ground so wet that no oxygen could seep in to speed their decay. More plants grew, and died, and grew and died again, layering the barren ground in first inches, then foot after foot of rich chocolate-colored peat. Once in a millenia, an ominous boom from the volcanoes across the bay turned the sky to black, smothering the plants in a layer of abrasive ash so thick it laid a bold stripe in the layers of mud and peat, still visible thousands of years later. All the smaller ashfalls have been spread out into nothingness, mere smears in the dirt.
Sweaty, with mud in his hair, shoulder deep in a giant hole, Hig told us this story, talking animatedly about all he was discovering in the layers of ash and mud, while Katmai perched curiously on the pile of overturned peat. I stood with my visiting parents, our rubber boots squelching on the surface of this cranberry-lined meadow, watching birds and chatting as Hig’s shovel uncovered the history (the hole was carefully filled in afterwards, and plants replaced). He’d been itching to do this for years – to dig down into the geologic history of this unusual meadow. Hig has loved digging holes since childhood, and is about as close as you can get to a PhD ditch digger.
He’s a sedimentary geologist. While we are both science geeks at a level I cannot deny, Hig is far more of a scientist than I ever was, yearning for graphs and measurements and careful data analysis while I am mostly content to learn more loosely, embracing numberless observations and telling stories. Sometimes, his science folds perfectly into our adventures, with Katmai peering into the hole in great excitement, as if every rock Hig unearthed was made of chocolate. Other times, it tumbles into conflict between careful measurement, detailed thought, and the chaos of children scribbling on notebooks and running off with crucial pieces of data. Toddlers and preschoolers make fickle field assistants.
This small dead pine was carefully sliced and measured, to figure out its rate of growth, and how much carbon it stored in its brief life.
Six or so years ago, a young pine seedling was planted in the clearcut below our house. Two winters ago, the upper five feet of its trunk was busted off by heavy snow. (It’s been sitting in our yard ever since). In the four years of growth recorded by this broken top, the tree stretched over a foot higher each year – nearly fifteen and a half inches on its best year. As it added rings of wood, it sucked carbon dioxide from the air, turning the intangible gas into lengthening branches and long fingery needles. Hig laid out the tree on a stretch of white cloth in a careful dissection, each segment cut and measured, each section of trunk polished to count the few wide rings. I shooed the kids (and their muddy boots) away from the edge, as he marked down columns of numbers. Each year the trunk captured more CO2 than the last… just a third of an ounce in 2007, then nearly an ounce, then three ounces, then nearly eight ounces.
Hig measures rings cut from a tiny pine tree, estimating its rate of growth and carbon sequestration
Climate change is shifting all the ecosystems around us. But what are the ecosystems doing to climate change? We watch the clearcut all the time, watching the non-native larch and pine seedlings shoot up beyond the native spruce, the alder cover old road beds, the berries and brambles spilling in profusion over the remain of old stumps, wondering what it will become. Hig’s measurements began to ask the less visible questions. How much carbon is going into the clearcut? Is it more, or less, than what went into the older forests around? How do the non-native pines compare to native spruce and alder for carbon uptake? If the forests were managed for carbon storage (rather than habitat or timber) what would the optimal management strategy be? When we burn firewood, what impact do we have on the carbon cycle? How many trees does it take to capture the carbon burned in our weekly van trips to town for lunch?
Inspired, Hig began a similar dissection of an alder, as Katmai borrowed the nippers to “help”, and Lituya began to investigate all the interesting little pieces of wood. Real science may have to come later.
After a storm, the signs of rapid coastal erosion are especially obvious. Here, spruce roots trail uselessly down to the beach, where the dirt has been washed away beneath them. Coastal Erosion Slideshow
Near the edge of the ice, a curtain of spruce roots trailed down a steep sand bluff. Their ends tangled with the greenish-brown piles of kelp at the top of the beach – forest abruptly meeting ocean. Fishing buoys and a dead skate, tossed up by the tide, littered the mossy forest floor at the ocean’s edge. Freshly broken trees, bright green and smelling strongly of spruce pitch, had toppled down onto the gravel beach below. I walked the edge of Malaspina Glacier on the Gulf of Alaska coast, watching global warming and the resulting erosion remake the world in front of my eyes.
It was the second time in a week I’d stood on this shore, and in that short time a storm had reshaped it completely. Stream mouths were re-routed. Great piles of logs had washed away, accumulating on new stretches of shore. We hunted for antique glass balls exhumed by storm waves and strewn in drift lines with green twigs and uprooted tube-worms. In a few places, the ocean had scraped away the sand altogether, revealing soft mud that offered little resistance to the crashing waves.
The base of this dead tree is washed by waves, on a shrinking beach on Alaska’s Lost Coast, near the rapidly-melting edge of Malaspina Glacier. Here, global warming is leading to rapid coastal erosion.
A huge part of the globe’s population and infrastructure is found on coastlines. Global warming is quickly becoming a driving factor in the reshaping of these shores – through a combination of sea level rise and beach dynamics. In the fall of 2011, I spent two months on Alaska’s wild Lost Coast, experiencing the impacts of global warming at the edge one of North America’s largest glaciers, and exploring the implications for the rest of the world.
During the storm, sea foam pelted our tent as we rolled boulders into place, anchoring the thin nylon walls. The intensity of the gale kicked up our adrenaline, and whipped the surf up into what seemed like monstrous curls. But with winds of perhaps 50 miles per hour, it wasn’t a 100-year storm, or a 10-year storm. It might not even be a 1-year storm. This happens all the time. Every year, or every few years, the waves come crashing into the trees. Here, on the melting edge of Malaspina Glacier, the beaches are washing away.
Once this was the Sitkagi Bluffs, but now the ice is melting and lakes and lagoons replace the towering ice.
In the middle of the wilderness, erosion harms little beyond the spruce trees. But around the world, shorelines are home to great metropolises and ports that move all the world’s goods. All are subject to the complicated dynamics that drive the formation and destruction of beaches, and vulnerable to changes in those forces. In most cases, global warming leads to increased erosion and endangers coastal communities.
We journeyed to Malaspina Glacier to explore the impacts of global warming first hand, bit the link between warming and coastal erosion turned out to be far more dramatic and interesting than I anticipated. So often, global warming-caused sea level rise is portrayed something like the filling of a bathtub. But coasts are far more dynamic, and vulnerable, than that image suggests. So how does it actually work? Read the rest of my essay here, see the coastal erosion slideshow, or see an example of melting and erosion at Malaspina as seen in photos and maps from the 1890s to today.
(Journal date 10-30-11)
It was a small and gentle stream, flowing out between mossy green boulders on a sunny afternoon, almost shallow enough to wade. Then it was a place of driving rain that stung our faces, driving sea foam that plastered the tents, gusts that lifted boulders from the tent stakes, thunder, lightning, and the deafening clatter of hail.
After the storm, high tide sent surges of water over our hastily abandoned camp. And the mouth of the lagoon had transformed–from a small and gentle stream to a roiling swatch of roiling white several hundred yards wide. Water poured out of the lagoon between giant breaks of surf that sent ocean waves crashing back in. A raft of logs was caught in the tug of war, battered and broken on the rocks until they were finally tossed all the way into the sea, streaming east down the coast with the waves. Salt spray filled the air, and waves splashed the rocks all the way to the top of the beach, where we stood to watch in the forest above. Evening brought a low tide, a flash of sun, and a retreat of the angry ocean. We walked between freshly-broken logs and clear blue icebergs, by the mouth of a small-again stream.
Malaspina is North America’s largest tidewater glacier. Four years ago, when we were first here, it squeaked by on a technicality. A few pieces of kelp, a stripe of sea foam at high tide, coming in through a narrow channel. Now it is unquestionable. The lagoon rises and falls with every tide, and tastes brackish even at the far end. Barnacles grow at the saltier depths. And the surf crashes in and out, sending icy blue chunks of Malaspina scattered along the coast. Sitkagi Lagoon is a place that doesn’t even exist on the USGS maps. A place that is still out of date on most recent satellite photos, and far longer then when we were here 4 years ago. Forest topped ice bluffs calve into the lagoon, and the mouse bite out of the massive Malaspina glacier grows larger and larger.
The children have slowed our pace and redefined our traveling style. Enough that people can communicate with us, airplanes can meet us, and instead of driving forward at a 15-20 miles per day pace, we’re the ones slowing folks down.
For the past week, we’ve been a party of 7. The four of us, plus Carl, a photographer and guide from Anchorage (who’s been with us for a couple weeks), Michael, a weather forecaster from Anchorage, and Sam, our programmer from Wisconsin. Sometimes, more people add more complications, driving us to camp in a terribly exposed spot none of us would have chosen on our own. But they lend helping hands holding a tent up in the storm, and adult conversation around our stove in the evening. They’re all headed out today after high tide, bringing this blog post with them. We were alone for nearly a month before Carl arrived. It will be odd to be alone again.
P.S. Thanks for all the questions. We’re happy to keep answering them. Sorry if any get lost in Sat Phone quirkiness.
I got my PhD studying tsunamis and working with other scientists who study tsunamis. One thing that almost every scientist studying tsunamis has in common is that they’ve never actually seen one.
For several of my former colleagues, this changed when the tsunami from Chile spread throughout the Pacific. Andy recorded 7 distinct waves using a ruler he’d just purchased at Home Depot in Santa Cruz harbor. Jody (my former advisor) and Tanya watched ice shift in tsunami waves in the frozen harbor of Petropavlovsk, Kamchatka (Russia). Jody has been studying tsunamis since the 80s. In an email she told us all, “I am SURE I eyewitnessed a tsunami, for the first time in my life!”
Tsunami scientist Tanya Pinegina watches gentle tsunami waves in the ice in Avacha Bay, Petropavlovsk, Russia.
Photo by Jody Bourgeois
All I can say is that I may have seen a tsunami, albeit a really small one. On a beach here in Seldovia I watched the dropping tide. Did it drop a little faster during the last 5 minutes? Has it slowed now? The tide gauge in town definitely saw something… a wave several inches tall with a period of 10 minutes or so (link here, many gauges on this page, including a more easily seen example of a tsunami recorded by a tide gauge in King Cove a few hundred miles southwest of Seldovia).
I also set up my camera. I took a timelapse video, accelerating reality by 300x. I’ve watched this video many times now, and I think I can see slight variations in how fast the tide drops down the beach near the center of the image. Then again, maybe not… you can judge for yourself. (The boat in the distance probably isn’t being moved by the tsunami, as the period of its motion is only 1-2 minutes, as opposed to about 10 minutes.)
The earthquake in Chile was a really big one. It’s amongst the largest ever measured, with the energy of a billion tons of TNT, enough to change the rotation of the earth. Decades pass without a single earthquake this large anywhere on the planet.
Does it seem like there are a lot of big earthquakes lately? Two recent deadly events, one in Haiti and one in Chile, have gotten a number people wondering if that is more than a coincidence.
In the case of Haiti and Chile, it almost certainly is just a coincidence. The earthquake in Haiti was a giant in terms of human tragedy, but as far as seismic energy, it was quite small in comparison to many earthquakes that have happened around the world lately. The USGS catalog records 16 earthquakes as large, or larger than the one in Haiti in the last year. The Haiti earthquake was large enough to increase the danger of other earthquakes on the same fault, but not large enough to influence tectonics a quarter of the way around the world in Chile.
However, the largest earthquakes – those over magnitude 8 – do seem to cluster in time. The three largest earthquakes in the 20th century, all magnitude 9 or more, occurred in 1952, 1960, and 1964. (Some catalogs list the 1957 Andreanof Islands earthquake as a 9.1, making four over 9 in that time range, but the USGS rates this one an 8.6.) After 1965, there were only two magnitude 8.3 earthquakes, and none higher until after the turn of the millennium. The statisticians have taken a look (Bufe and Perkins, 2005), and they don’t think that’s random. I plotted the data below, and you can judge for yourself.
We’ve been measuring earthquakes since 1900, and the recurrence of the largest ones doesn’t seem random. There’s a clump of large earthquakes in the ’50s and ’60s, and then a lull through the turn of the Millenia. Things have been more active again in the past decade.
Click the graphic for a larger version, as well as data and vector graphic file.
And the past decade has been a big one for earthquakes. There have been five earthquakes above 8.3, including the 2004 magnitude 9.1 earthquake in the northeastern Indian Ocean. Each increase of 0.2 in magnitude corresponds to a doubling in energy released, so the 2004 magnitude 9.1 released as much energy as 16 magnitude 8.3 earthquakes.
What does this mean? We only have a short instrumental record (since 1900) and there’s a lot of variability, so it’s impossible to know whether we have another magnitude 9 just around the corner. But it seems likely that the period of tectonic quiescence starting in 1965 and ending with the gradual increase in seismicity in the late 90s is gone. It’s no time to dally on the science, both old-fashioned paleoseismic studies, and maybe some new methods that can help warn of impending earthquakes. And it’s no time to skimp on education and good infrastructure that can save lives during an earthquake. Likely the biggest difference that led to far fewer people killed in Chile than in Haiti was better building standards.
At this point we don’t really know.
For an earthquake on a fault to happen, there have to be two things in place: The fault has to be under stress so it can provide energy for an earthquake, and some point has to fail, triggering the fault to move and that energy to be released. Stress increases over time and eventual failure is inevitable, but exactly when it happens is dependent on that trigger, which can be very subtle. The point where failure begins is the hypocenter (directly beneath the epicenter on the surface of the earth) and the entire portion of the fault that moves is the rupture area.
One way to think of it is to imagine the fault as a large building. Perhaps it is an apartment building in Istanbul, and as new floors are illegally added the stress on the structure increases. This unstable structure has a lot of energy in it, all in the form of cement and other materials suspended high in the air by weak architecture. But when it finally collapses, that collapse starts somewhere. Perhaps a pillar designed for two stories and holding five collapses because someone uses it to tie up their dog. Now the nearby pillars and walls must suddenly bear more of the weight, and they collapse as well. The failure spreads from the original “epicenter” pillar, and consumes the entire building, analogous to the earthquake’s rupture area.
So was it the dog that caused the building to collapse, or the extra stories? I’d say the cause was the additional stress, while the trigger was the dog. Earthquakes are the same way… caused by gradually building stress, but triggered when some point gives way.
Bufe and Perkins, 2005, discuss how an earthquake in one area of the world might lead to another far away and years later. Their first possible explanation focuses on triggering, while the others suggest that stress might increase on distantly separated faults at the same time: