Stories tagged Earth Structure and Processes


A river scientist takes two measures of the rate at which sediment moves along the bed of a river (the sediment transport rate). The measurements are taken a few minutes apart but yield wildly different results. What went wrong? Why measure sediment transport in the first place?

Early in fall of 2008, Arvind Singh, a Ph.D. student with the National Center for Earth-surface Dynamics (NCED), used a flume (think water moving through a channel) experiment at the U of MN's Saint Anthony Falls Laboratory (SAFL) to demonstrate a phenomenon that had long plagued river scientists: field measurements of sediment transport rates are typically highly variable, depending on the location or amount of time over which the sample is collected. Arvind and his collaborators wanted to find a way to make the measurement reliable.

Not being a river scientist, it was a little unclear to me why accurate measurements of sediment transport are so important, but it turns out that understanding sediment transport is essential for almost any river management endeavor. Algal growth, fish habitat, and river flooding may all be influenced by small- or large-scale fluctuations of sediment transport. Arvind and colleagues wanted to determine the time that an individual would need to sample to obtain a representative average sediment flux, or, for that matter, whether it was even sensible to try to characterize such a measurement for a real river.

From his 2008 work at SAFL, Arvind was able to demonstrate that measurements of bed topography and turbulence can be used to obtain reliable measurements of sediment transport: both topography and turbulence will indicate the sampling time interval that is adequate to get a measurement of the average sediment transport rate for a given river.

From his 2008 work, Arvind also gained insight into the importance of variability in characterizing sediment transport. Since most sediment transport models employed in the field incorporated measures of mean sediment transport but not of variability in sediment transport processes, Arvind set out to characterize the randomness of sediment transport.

Arvind’s current experimental work involves measuring sediment transport under laminar flow conditions to remove the effects of turbulence and reveal the effect that particle-particle interactions have. He plans to run his flume experiments, with help from SAFL intern Kristin Sweeney, through April and analyze the data this spring to reveal more about the randomness involved in sediment transport.


A dam is removed from a mountain waterway. What happens to the 750,000m3 of sediment that has accumulated behind that dam? Chuck Podolak, a Ph.D. student with the National Center for Earth-surface Dynamics (NCED), is using a flume experiment at the U of M's Saint Anthony Falls Laboratory (SAFL) to help him understand just that question.

In 2007, the Marmot Dam was removed from the Sandy River in Oregon, releasing 750,000m3 of sand and gravel that had accumulated behind the dam. At the time, the breach represented the greatest release of sediment from any U.S. dam removal. Chuck's goal is to understand how all that sediment will affect the river’s bottom.

Chuck’s work will help predict how bed topography in mountain rivers like the Sandy will respond to dam removal, or how large-scale gravel additions that are occasionally employed downstream of dams will affect bed forms that are beneficial for fish spawning and habitat.

One arm of Chuck’s Ph.D. research endeavor is his recent flume experiment at SAFL. Peter Wilcock, Chuck’s adviser, described the work to me as a Sisyphean task, and he did so with good reason. With help from SAFL staff and researchers, Chuck spent several weeks removing sediment from the bottom of an indoor 9 ft x 250 ft x 6 ft flume (SAFL’s “main channel” facility), shoveling tons (literally) of it back into the flume, collecting it at the flume’s mouth, and adding it to the channel again.

Chuck is using a customized instrument set-up to take laser scans and make centimeter-scale maps of the flume bottom. The measurements will give him an extremely detailed look at the flume bed, tracking down where the added sediment ended up: in pools, on top of bars, or in new bars. After the experiment’s conclusion, Podolak will combine its revelations with data gathered from field studies to run computer experiments that will shed new light on bed topography dynamics in gravel-bedded rivers.

Here is a movie I made about Chuck's experiment:

Chuck also created time series renderings of the topography in the main channel flume at SAFL during his Feb-Mar 2010 sediment addition experiment. Orange background indicates times of sediment additions:


Strike-slip fault
Strike-slip faultCourtesy USGS
Last weekend’s massive magnitude 8.8 earthquake off the coast of Chile released 500 times the energy generated by the magnitude 7 earthquake that hit in Haiti the month before. Damage is extensive in both countries but so far Haiti seems to have taken a worse hit than Chile, despite suffering a less-powerful quake. In fact, there's news today that the death toll in Chile has been lowered, which is unusual with earthquake tolls. They're usual revised upward. So why the discrepancy between the two quakes? There are several reasons but a big one is the types of earthquakes involved.

The Haiti tremblor occurred along a strike-slip fault where stress is created as two tectonic plates (in Haiti’s case, the Caribbean plate and North American plate) scrape and grind past each other in opposite directions, like two cars trying to squeeze past each other on a single lane bridge. Tension builds as the plates catch and grind and energy is released in fits and starts in the form of tremors. California’s San Andreas fault is a classic strike-slip boundary. There the Pacific plate is moving in a northwesterly direction beside the North American plate.

Subduction zone: Megathrust earthquakes occur near subductions zones.
Subduction zone: Megathrust earthquakes occur near subductions zones.Courtesy USGS
With a subduction zone megathrust quake – like that which occurred in Chile - it’s more like a head-on collision, where a lighter oceanic crust slams into a heavier continental crust and pushes (or is pulled) beneath it. This creates tremendous tension which eventually gets released, and when it is does, megathrust earthquakes can sometimes occur. They don’t occur all the time, in fact, megathrust earthquakes are rare – only fourteen have been recorded in history – but they only happen in subduction zones, like the one along the coast of Chile where the oceanic Nazca plate is subducting beneath the continental South American plate. Chile’s Andes mountain range rose up as a result of this subduction.

To give an idea of the incredibly huge amount of energy involved with the Chilean quake, it’s been estimated the jolt shifted Earth’s axis 3 inches, caused the planet’s entire mass to contract, become denser, and it’s rotation to speed up, thereby shortening the length of a day by 1.26 milliseconds! (see story)

The nearness and depth of an earthquake’s epicenter is another factor in the amount of perceived intensity and actual damage (measured using the modified Mercalli Intensity Scale), and this figures in the Haiti-Chile comparison. Haiti’s tremblor occurred six miles below the surface, and within ten miles of the severely over-populated capital of Port-au-Prince. That’s a fairly shallow earthquake, so the intensity level was high. Chile’s earthquake was centered 22 miles underground and five miles offshore, more than 70 miles from the nearest large population center (Concepcion).

Haiti’s capital is also built on loose soil that’s been eroded and carried down from the hillsides, and since earthquakes are rare in the region, the poor island nation is ill-prepared and under-equipped to deal with them. Building construction is flimsy, and collapsed easily when shaken, even by many less intense after-shocks. Chile, however, is on solid bedrock, both geologically and in regards to their central government. The country has a long history of dealing with the many quakes that occur there (the normal-sized ones anyway), and has had building codes in place since the 1920s.

More earthquake information
USGS earthquake page


The Enriquillo fault: Only the western half of the Enriquillo fault ruptured during Haiti's January earthquake.
The Enriquillo fault: Only the western half of the Enriquillo fault ruptured during Haiti's January earthquake.Courtesy Mikenorton
Haiti’s January 12th earthquake occurred on a strike-slip fault that runs in an east/west direction through the country. The fault, known as the Enriquillo fault, is where the North American and Caribbean tectonic plates meet. The jostling of these plates caused a quake that measured 7.0 on the Richter scale, killed approximately 217,000 people, destroyed 280,000 residences and commercial buildings, and left over one million people homeless. It has been deemed the most destructive natural disaster that a single nation has endured. Unfortunately, geologists believe that another, equally destructive quake could occur in Haiti within the next 20-30 years. Using high-resolution radar images of the Enriquillo fault after the quake, geologists from the University of Miami found that only half (the western half) of the fault had surged. They speculate that the remaining energy still locked up in the earth is what will cause the next quake on the eastern portion of the fault.

The radar images also showed that the earthquake produced a lot of vertical motion, not typical in strike-slip faults. This vertical motion, say geologists, explains how such a small fault movement could cause such a large earthquake. From their analysis, geologists are recommending that Haiti move all of its essential infrastructure (schools, hospitals, etc.) north, out of the fault zone.

This is a great example of science being used to help avoid future devastation, or at least lessen future destruction. Knowing that there is still potential danger along the Enriqillo fault allows people to plan accordingly (i.e. building or rebuilding in a safer location). However, this is also a case where I hope science is wrong.


A satellite image of the East Siberian Sea from USGS
A satellite image of the East Siberian Sea from USGSCourtesy United States Geological Survey
When I read this story the other day, I thought to myself: why didn't I think of that? Or maybe I did think of it, but as usual no one was listening when I pitched the idea for an action-packed spy movie about climate change. Or were they?

The Central Intelligence Agency does have a bunch of high-powered satellites and other "classified" instruments, so it's possible they've been using them to eavesdrop on my conversations with friends about possible sci-fi movie plots.

What's more likely: they figured out on their own that intelligence-gathering instruments could be really helpful to scientists, who can read detailed pictures of melting sea ice, growing desserts and other phenomena to better understand how climate is changing the planet.

The C.I.A. recently confirmed that it had revived this controversial data-sharing program known as Madea, which stands for Measurements of Earth Data for Environmental Analysis. If you decode that C.I.A. code name, it means that government spies are working with climate scientists to gather images and data about environmental change, as well as its impact on human populations.

Not everyone is convinced that climate change is a real threat to national security, and so some complainers are complaining that this collaboration between scientists and the C.I.A. is a misuse of resources, but what do they know?

Really? What do they know? So much of what happens over at C.I.A. headquarters is top-secret.

Maybe the whole thing doesn't sound that action packed, but I'm telling you, if you had the right actors playing the scientists, it could be a blockbuster. And if you have the right scientists analyzing the data, it might provide really valuable insights into global environmental change.


GOCE Satellite: The Gravity field and steady-state Ocean Circulation Explorer
GOCE Satellite: The Gravity field and steady-state Ocean Circulation ExplorerCourtesy ESA
Can it be true? Yes, for a mere $5,544 dollars round-trip airfare to Greenland! In March 2009, the European Space Agency launched the Gravity field and steady-state Ocean Circulation Explorer (GOCE) into orbit around our planet, which is now transmitting detailed data about the Earth’s gravity. The GOCE satellite uses a gradiometer to map tiny variations in the Earth’s gravity caused by the planet’s rotation, mountains, ocean trenches, and interior density. New maps illustrating gravity gradients on the Earth are being produced from the information beamed back from GOCE. Preliminary data suggests that there is a negative shift in gravity in the northeastern region of Greenland where the Earth’s tug is a little less, which means you might weigh a fraction of a pound lighter there (a very small fraction, so it may not be worth the plane fare)!

In America, NASA and Stanford University are also working on the gravity issue. Gravity Probe B (GP-B) is a satellite orbiting 642 km (400 miles) above the Earth and uses four gyroscopes and a telescope to measure two physical effects of Einstein’s Theory of General Relativity on the Earth: the Geodetic Effect, which is the amount the earth warps its spacetime, and the Frame-Dragging Effect, the amount of spacetime the earth drags with it as it rotates. (Spacetime is the combination of the three dimensions of space with the one dimension of time into a mathematical model.)

Quick overview time. The Theory of General Relativity is simply defined as: matter telling spacetime how to curve, and curved spacetime telling matter how to move. Imagine that the Earth (matter) is a bowling ball and spacetime is a trampoline. If you place the bowling ball in the center of the trampoline it stretches the trampoline down. Matter (the bowling ball) curves or distorts the spacetime (trampoline). Now toss a smaller ball, like a marble, onto the trampoline. Naturally, it will roll towards the bowling ball, but the bowling ball isn’t ‘attracting’ the marble, the path or movement of the marble towards the center is affected by the deformed shape of the trampoline. The spacetime (trampoline) is telling the matter (marble) how to move. This is different than Newton’s theory of gravity, which implies that the earth is attracting or pulling objects towards it in a straight line. Of course, this is just a simplified explanation; the real physics can be more complicated because of other factors like acceleration.

Albert Einstein
Albert EinsteinCourtesy none
So what is the point of all this high-tech gravity testing? First of all, our current understanding of the structure of the universe and the motion of matter is based on Albert Einstein’s Theory of General Relativity; elaborate concepts and mathematical equations conceived by a genius long before we had the technology to directly test them for accuracy. The Theory of General Relativity is the cornerstone of modern physics, used to describe the universe and everything in it, and yet it is the least tested of Einstein’s amazing theories. Testing the Frame-Dragging Effect is particularly exciting for physicists because they can use the data about the Earth’s influence on spacetime to measure the properties of black holes and quasars.

Second, the data from the GOCE satellite will help accurately measure the real acceleration due to gravity on the earth, which can vary from 9.78 to 9.83 meters per second squared around the planet. This will help scientists analyze ocean circulation and sea level changes, which are influenced by our climate and climate change. The information that the GOCE beams back will also assist researchers studying geological processes such as earthquakes and volcanoes.

So, as I gobble down another mouthful of leftover turkey and mashed potatoes, I can feel confident that my holiday weight gain and the structure of the universe are of grave importance to the physicists of the world!


Floating Free on the Dead Sea
Floating Free on the Dead SeaCourtesy Courtesy of Ranveig at Wikimedia Commons
In anticipation for the Dead Sea Scrolls exhibit coming to the Science Museum of Minnesota, I found myself wondering, why do we call it the Dead Sea? The Dead Sea is the lowest place on earth and one of the saltiest bodies of water in the world, 6 to 10 times saltier than the Atlantic Ocean. Because the salt creates such a harsh living environment, the only organisms that will survive in the Dead Sea are bacteria and algae. Any fish that accidentally swims into the Dead Sea from one of the freshwater streams that feed it, like the Jordan River, would die instantly!

The sea is so salty because of evaporation. The high temperatures and low humidity in the region cause the water in the sea to evaporate very quickly, leaving behind all the dissolved mineral salts. Some salts sink to the bottom and some wash ashore leaving a salty crusty beach.
Dead Sea Salt Beach
Dead Sea Salt BeachCourtesy Courtesy of Isewell at WikiMedia Commons

Because of the high concentration of mineral salts in the Dead Sea, the water is more dense than both freshwater and the human body. This means that our bodies become buoyant, like a cork, and we can easily float on it. When you take a dip in the Dead Sea you can actually kick back and read a book like floating on a raft. In fact, it is hard to actually “swim” in the sea.
Dead Sea Salt
Dead Sea SaltCourtesy Courtesy of Xtall at WikiMedia Commons

The Dead Sea has been a tourist attraction since the time of Herod the Great in the 1st Century BCE. The Dead Sea isn’t just a novelty for “fun while floating” but the mineral salts have been used in Egyptian mummification, in agricultural fertilizers and even in modern day cosmetics. Check out these links to learn more about Dead Sea geography, how it was formed, how it is used by humans, and some of the issues it faces today.


Trailhead sign
Trailhead signCourtesy Mark Ryan
In the latter days of summer my wife and I took a drive up the Gunflint Trail and visited the Magnetic Rock Trail, a spur trail jutting off the Gunflint near Gunflint Lake. Our original plans of lounging about the North Shore of Lake Superior had been scuttled by a mix-up in our cabin reservations, so I saw it as an opportunity to check out first-hand some of the local geology. I had visited the MRT briefly once before and my reasons for wanting to make the 50-mile drive from Grand Marais to revisit the trail were three-fold: stromatolites, meteorite impact ejecta, and, of course, magnetic rocks

Well, as it turns out, I wasn’t very successful,

Signs of recent fire: Evidence of forest fire can still be seen along the Magnetic Rock Trail.
Signs of recent fire: Evidence of forest fire can still be seen along the Magnetic Rock Trail.Courtesy Mark Ryan
Readers may recall the Ham Lake forest fires raged along the Gunflint Trail in the early summer of 2007, destroying several hundred acres of the surrounding forest along with resorts and private property. The fire, it was later determined, was started by a legal campfire in the vicinity of Ham Lake that had gotten out of hand and spread quickly through the region. It was the second forest fire to rage through the Magnetic Rock Trail (MRT) in the past two decades (there was also a controlled burn in 2002). The latest fire removed much of the pine canopy that covered the area, opening it to more sky and sunlight, and new vistas of the surrounding terrain.

Idyllic scene at a pond along the Magnetic Rock Trail
Idyllic scene at a pond along the Magnetic Rock TrailCourtesy Mark Ryan
A new jack pine rises from the ashes
A new jack pine rises from the ashesCourtesy Mark Ryan
But as destructive as forest fires can be, they do have their upside. Forests are quick to revitalize after fires. New trees soon rise up from the ashes, and evidence of that in the MRT was apparent in the many jack pines (Pinus banksiana) we saw sprouting up everywhere. But trees aren’t the only affected flora. A lot of the groundcover gets incinerated as well, sometimes exposing patches of bedrock. In the case of the Magnetic Rock Trail, it meant new outcrops of the Gunflint Iron Formation were uncovered, revealing fresh unexplored exposures.

The Gunflint Iron Formation is a mass of iron ore taconite that spans from the Arrowhead region of Minnesota eastward into Ontario, Canada with the majority of the formation located on the Canadian side of the border. Most iron formations on Earth were formed around the same time, about 2 billion years ago during the Middle Pre-Cambrian (Early Proterozoic) times. A shallow sea (the Animikie) covered much of northern Minnesota and eastern Ontario at the time. The sea teemed with cyanobacteria in the form of stromatolites; thick microbial mats that helped oxygenate the Earth’s atmosphere and metabolize iron out of solution through photosynthesis. The iron-oxide sediments later became the iron ranges that span across northern Minnesota and Canada. Much of the rock along the Magnetic Rock Trail is composed of magnetite (Fe3 O4) inter-bedded with layers of chert or shale. Magnetite is the most magnetic of all the naturally occurring minerals, hence its name. The Gunflint Iron Formation is particularly resistant to erosion on the Minnesota side probably due to its nearness to the Duluth Complex intrusives. These influxes of magma moved into the area around 1.1 billion years ago, adding tremendous heat to the existing strata. The portion of the Gunflint Iron Formations (that located in Minnesota) closest to the heat source shows the most resistance to erosion.

Stromatolites and not?: Stromatolites by geologist Jim Miller, MN Geological Survey (top); maybe not stromatolites by author (bottom)
Stromatolites and not?: Stromatolites by geologist Jim Miller, MN Geological Survey (top); maybe not stromatolites by author (bottom)Courtesy Jim Miller, MN Geological Survey (top) Mark Ryan (bottom)
Preserved within some of the newly exposed outcrops along the MRT are fossil records of these stromatolites, representing some of the oldest fossils found in Minnesota. Gunflint stromatolites contain large numbers of fossils that can be seen under a scanning electron microscope. I had been told that you can walk off the main path and find some of these ancient fossils, so I searched off-trail for a while and found what I thought were stromatolites, and took photos of them.

But later when I consulted with geologist Mark Jirsa, he wasn’t so sure.

“You're looking at thin bedding in the iron formation that dips shallowly in comparison to the dip of the outcrop surface,” he wrote me. “The result is a swirly look, that looks deceptively like stromatolite mounds.”

Jirsa was in the field when I contacted him, and his Internet capability was limited, so when he tried to send me some photos of what the stromatolites actually looked like, they didn’t come through. However, his colleague, geologist Jim Miller (who also supplied welcomed assistance with this post) sent me a stromatolite photo he had taken at MRT.

Personally, I can’t tell the difference, but then I’m no geologist. so I have to bow to the professionals.

My second quest – to locate and photograph ejecta from the Sudbury Impact – wasn’t successful either. The aforementioned Mark Jirsa discovered this record of a 1.85 billion-year-old meteor impact in 2007. I wrote a previous post about it that same year so I won’t go into those details (you can read it here) but I will bring you up to speed on how he’s since interpreted the find.

Briefly, the Sudbury Impact Crater is located in Ontario, Canada, and was made by a meteorite about 10-miles in diameter that slammed into the Earth 1.85 million years ago. The 150-mile wide crater is the second largest known on the planet. The collision sent a tremendous firestorm of superheated material into the atmosphere, and some of it coalesced like hailstones and landed 480 miles away in northeastern Minnesota. This is what Jirsa discovered two years ago: a layer of ejecta mixed with torn up pieces (breccia ) of the Gunflint Formation, and all of it overlain by a younger layer of slate known as the Rove Formation. He published an article about it in Astronomy magazine, and there’s also a PDF file downloadable from Minnesota Geological Survey website (the link is located in the upper left of the MGS homepage).

Debris from Sudbury Impact found in Minnesota: Photo by Mark Jirsa, Minnesota Geological Survey
Debris from Sudbury Impact found in Minnesota: Photo by Mark Jirsa, Minnesota Geological Survey
What Jirsa found was quite remarkable: a layer of churned-up rocks laid down above the Gunflint Iron Formation. The odd jumble of rock included berry-shaped rocks known as accretionary lapilli, intermixed with the Gunflint Iron Formation rock. According to his interpretation, what is seen in the layer essentially shows the events of a single day in the geological record. And a nasty day it must have been.

Three minutes after the initial fireball impact at Sudbury, seismic waves from earthquakes measuring more than magnitude-10 on the Richter Scale reached the Animikie basin, ripping loose the iron formation off the seafloor crust, and redistributed it along a submarine slope. Within 10 minutes, a firestorm of molten material hailed down from the sky covering the region with from 3 to 10 feet of ejecta in the form of accretionary lapilli. Ultra-hurricane-force winds measuring up to 1400 mph(!) blasted over the shallow sea soon after, followed by the coup de grace – titanic tsunamis the likes of which have never been seen since which tossed everything into a stew of breccia (jumbled rock) and berry-shaped ejecta.

This day of horror took place sometime in the 48 million year interim that separates the Gunflint Iron Formation and the time the sediments of the Rove Formation were laid down above it. The entire concoction was later baked and metamorphosed by the intrusive magmas of the Duluth Complex.

How hard could it be to find evidence of a mess like this? Well, considering the MRT covers a large area, and since I had no information pinpointing any locations, it was like looking for a needle in a haystack – a very large haystack. In the end, I soon gave up because I really didn’t know what I was looking for and I realized how futile it probably would be. However, I’ve sure learned a whole lot about it now.

Magnetic Rock Trail's rocks are magnetic: as my handy magnet proves.
Magnetic Rock Trail's rocks are magnetic: as my handy magnet proves.Courtesy Mark Ryan
Initially, I thought at least my third quest – finding magnetic rock – would be a complete success because just about every rock exposed along the MRT is highly magnetic (I had a magnet with me and I can attest to that fact – see photo). It made sense that the whole reason the trail is called the Magnetic Rock Trail is because of all the magnetic rocks found there. But I’ve since learned I was once again totally wrong. The trail is name after a single large magnetic rock that’s about 1.5 miles up the trail. This 30-foot monolith stands upright and obvious in the middle of the forest and its notoriety dates back to early native American times. It is a chunk of the Gunflint Iron Formation – and highly magnetic like the rest of the rock in the area – but is deemed an erratic moved into place from a short distance away by glaciers during the last Ice Age. Had I read any of the brochures I had collected on our trip sometime other than when I got home, I would have known this before I even got there. But as it was, we didn’t walk that far into the trail so we missed it completely. Oh, well.

Blueberry picking: Mrs. R collects blueberries near the Magnetic Rock Trail.
Blueberry picking: Mrs. R collects blueberries near the Magnetic Rock Trail.Courtesy Mark Ryan
But even though my three main objectives for visiting the MRT were pretty much complete washouts, there was one unexpected surprise that will probably draw us back to the region next year: blueberries.

Blueberries and metamorphism: The real attraction at the Magnetic Rock Trail?
Blueberries and metamorphism: The real attraction at the Magnetic Rock Trail?Courtesy Mark Ryan
Wild blueberries (Vaccinium angustifolium) were all over the place. The low-bush berries thrive in sandy, acid soils of forest clearings, and in rocky areas around pines forests – just the type of environments you find around the MRT. So, once I finished with my failed geological studies, I assisted my wife in picking as many wild blueberries as we needed. We kept them in our cooler for the ride home, and as Mrs. R is prone to do, she jumbled all the berries together into a viscous concoction, all within a flakey crust that was heated over time at a very high-temperature.

The result looked something like the Sudbury Impact ejecta layer found near the Magnetic Rock Trail, but it was much more delicious, and a great way to end the summer.

Forest regrowth on Buzz
More about stromatolites
Top Ten Most Impressive Impact Craters
More about Minnesota geology