Is the Grand Canyon showing its age?

It might be one of the best studied geologic features in the country, and it's certainly one of the most striking, but a scientific debate continues to rage over the Grand Canyon. Specifically over what's typically considered an impolite question: how old is it?

Many geologists estimate that the Colorado River began to carve the canyon we see today between five and six million years ago. But in December, a paper published in Science presented evidence that the western portion of the canyon might have been carved close to the present depth by 70 million years ago.

The week, Science hosts two comments challenging the ancient canyon proposal and a defense of the controversial paper from its authors. This is science in action—researchers debating a 65 million year conflict between evidence from traditional geological methods and new dating technology.

Read 8 remaining paragraphs | Comments

NOVA series tours Earth history, Aussie style

Host Richard Smith with the modern stromatolites of Shark Bay.

Chris Taylor

It’s the geologist’s refrain: rocks tell stories. Geologists don’t (usually) get excited about a chunk of sandstone just because it’s sandy. It’s the secrets it holds—secrets about a world in the past that we can never visit, even as we stand on its consequences.

“Australia’s First 4 Billion Years," a four-part series that begins April 10th on NOVA, recounts the tale of Earth’s history the right way—by letting the rocks tell it. And it does so without even leaving the land down under (save a short stop in New Zealand).

That’s not a limitation, it’s a strength. It allows the program to hone in on details that many won't have heard before, rather than providing a montage of interesting events around the world—an approach that usually yields only the most familiar ones. The program builds an appreciation for the landscape, too, by allowing you to more fully explore the rich history of a region. Besides, Australia’s geology lays bare an impressive amount of geologic time. You could do much worse as far as locations go.

Read 8 remaining paragraphs | Comments

Earth’s orbital cycles may trigger peaks of volcanic eruptions

Icelandic volcano Eyjafjallajökull erupting in 2010

fridgeirsson

Over the past couple million years, a rhythmic pattern of climate changes have been driven by cycles in Earth’s orbit. These cycles affect the sunlight reaching the Earth, altering seasonal patterns and leading to growing or shrinking ice sheets. The changes echo throughout the Earth, from atmospheric and ocean circulation to ecological responses and even erosion and sediment transport. But could the cycles have affected volcanic eruptions?

A new study published in Geology argues that they did. Previously, researchers have noticed correlations over limited time periods and regional scales, but the new work extends this to a broader picture, and appears to show a pretty strong link.

To get long records of volcanic eruptions, the researchers used marine sediment cores from around the Pacific Ring of Fire. Unlike on land, where erosion can wash away ash layers, the records in the seafloor sediment preserve the ash from eruptions that occurred upwind of their location. Errors in the dates assigned to those ashes, which are based on correlating those layers with well-dated ones on land and estimating the rate at which sediment piles up on the seafloor, are difficult to avoid, but the researchers did their best to account for that uncertainty.

Read 8 remaining paragraphs | Comments

GigaPan’s gigapixel images bring field trips to geology classrooms

Screengrab from a GigaPan taken at Dinosaur National Monument in Utah. Image by Ron Schott.

As I can attest firsthand, one of the biggest obstacles to getting students engaged in geology courses is being stuck in a classroom. It’s a science meant to be taken in by striding up hills and with a liberal application of hammers. And while it’s immensely beneficial to tackle the basic principles using simplified models and diagrams, it's hard to really appreciate them until you’ve seen them in the stony flesh, connecting with an unfamiliar Earth that's millions or even billions of years in the past.

In a world of tight class schedules and even tighter budgets, opportunities for excursions to the field are few, so the challenge is to bring as much of the outside world into the classroom as possible. Recently, a new tool has made it a little easier for educators to do just that.

That tool is the beautiful, explorable imagery created by GigaPan. The technology uses motorized mounts that guide a camera through snapping hundreds of high-resolution pictures that cover a predefined area. The images are subsequently stitched together to build a gigapixel (or more) scene that makes a standard panorama look like it came with a kids’ fast food meal.

Read 13 remaining paragraphs | Comments

Want to study craters? Geologists grab explosives and make some

Enlarge / View from the edge of Kilbourne Hole in New Mexico—an example of a maar crater.

Scott K. Johnson

While craters cover many other bodies in the solar system, plate tectonics and weathering continually renew the Earth’s surface, preserving its youthful beauty. Still, that process doesn't happen overnight, and there are many craters to be found on our planet. Some record violent impacts with meteorites, and others formed during a variety of volcanic eruptions.

Maar craters, like the one pictured above, are created when fingers of magma beneath the surface of the Earth interact with groundwater, causing a violent explosion. Measuring the size of a meteorite impact crater can provide a lot of information about the size and impact angle of the meteorite. But when it comes to maar craters, geologists have been unsure just how much information about the eruption can be gleaned from the remnant crater.

Part of the problem results from the explosion being able to occur at a range of depths. An explosion of the same size could create a very different crater at the surface depending on how deep it occurs. To complicate matters further, there can sometimes be multiple eruptions beneath the same crater.

Read 12 remaining paragraphs | Comments

“Sombrero” mountain growth in the Andes rides on rising magma

Uturuncu, a volcano at the center of the uplifting area.

Wikimedia Commons

Most of us are familiar with igneous rocks that form in volcanic settings, as lava crystallizes into rock while cooling quickly. It’s easy enough to envision this process since it occurs right before our eyes or at least some cameras (and besides, thousands of science fairs across the country probably display a baking-soda-and-vinegar analog each year).

But what about the igneous rocks that form deep below the surface—like the beautiful granites that are so popular for kitchen countertops? It’s not so easy to imagine how these massive bodies of magma—called “intrusions”—rise through the Earth’s crust before stopping and slowly solidifying, sometimes feeding a volcano at the surface during the process.

Geologists have argued about how this material rises for a long time. Several models have been proposed that would allow this magma to reach its destination; some researchers have proposed a process called “stoping,” where slabs of rock continually fall off the roof of the magma chamber. In this way, the magma could gradually chew its way upwards.

Read 7 remaining paragraphs | Comments

Can humans cause an earthquake?

St. James Church in Lorca, Spain after an earthquake on May 11, 2011.

Wikimedia Commons

One of the things people often wonder about earthquakes is whether human activity can play a role in their occurrence. Sometimes that comes from a desire to assign blame, but often it’s related to a bigger question: could we actively trigger small earthquakes to prevent the big, damaging ones from occurring? While that lofty piece of geoengineering may not be feasible (or even possible), it is true that humans can sometimes trigger earthquakes.

Earthquakes are fundamentally controlled by two factors. The first is the movement of rock, such as tectonic plates. This constant, gradual movement is the source of conflict in an active fault zone—one region of rock is being forced past another. If the two blocks simply slid smoothly by each other along the fault surface, this would be a pretty peaceful process. But this is where the second factor comes along—the friction between the blocks. The stress builds up until it’s great enough to overcome that friction, at which point seismic energy is released violently as the blocks catch up on decades' (or centuries') worth of motion in just a few seconds.

For the most part, the accumulating stress that creates this situation is much too large for human activities to make a difference. We can, however, affect the friction that locks up the fault. Hydraulic fracturing, where fluids are pumped into the ground at extremely high pressures to crack rocks that release natural gas and oil, has been shown to do just that in certain situations. Increasing the fluid pressure inside the fault partially de-stabilizes the friction-lock, lowering the stress threshold necessary to trigger an earthquake just enough for one to occur.

Read 11 remaining paragraphs | Comments

Bermuda’s golf courses sit on land that’s (partly) an African import

Enlarge / Bermuda's red soils sit atop limestone bedrock.

Photo by Diana Johnson, University of Illinois

The characteristics of a region’s soils are largely controlled by two factors: climate and geology. Soils are mostly composed of broken-down minerals from the bedrock (along with, critically, organic matter), and the weathering process is driven by climatic conditions. Soils can also form within the sediments deposited in an area, however, as is the case in the flood plains of river valleys. And there are other things that can transport sediment to a new home—like wind.

This is what makes the soil of the island of Bermuda so interesting. It seems like they don’t belong. The island’s shallow bedrock is composed of gray limestone, mainly in the form of broken-up bits of skeletons from marine organisms—the same stuff that makes up the beach sand. The soil, however, is rusty-red and clay-rich.

The reason for this sharp contrast has long been debated, with two hypotheses gaining the most support. One possibility is that the limestone contains a fair amount of clay, which is left behind as the limestone dissolves. (Limestone weathers quickly in rainwater, as evidenced by hard-to-read gravestones.) In this view, it’s not that the clay soil “doesn’t belong”, it’s just that it’s concentrated by the removal of the other minerals.

Read 7 remaining paragraphs | Comments

No absolutes: How shifting plates completely remake the Earth

NASA

Plate tectonics is one of the most successful theories in the history of science. Beyond its scientific successes, it's widely accepted by the public, since it explains a lot about the world that we see around us.

But like other successful theories, it has its share of awkward inconsistencies. A recent paper in the Journal of Geophysical Research attempted to tackle one of these inconsistencies—finding an absolute reference frame for the movement of the plates—but failed so badly that its authors advise other scientists not to even bother trying. But as part of their failure, they came up with a new measure of one of the more unexpected consequences of plate tectonics.

All of plate tectonics is driven by density differences in the material beneath our planet's solid surface. These drive the shifting plates, power hot-spot volcanoes, and recycle material to the planet's surface. They also make sure that the mass of the Earth is never evenly distributed. As that mass shifts internally, it actually causes the Earth's spin to wobble around a bit. As a result, even the Earth's axis of rotation doesn't provide an absolute reference frame. In the process of failing to find an absolute reference frame, though, the authors have provided a detailed map of how the Earth's true pole has wandered over millions of years.

Read 17 remaining paragraphs | Comments

Mid-plate earthquake a product of tension between India, Australia

A map of the areas that ruptured during the largest mid-plate earthquake yet witnessed.

Keith Koper

Back in April, we reported on a remarkable earthquake off the Indonesian island of Sumatra, near the location of the magnitude 9.1 quake that caused the devastatingly deadly tsunami in 2004. The more recent event caused little damage despite the fact that it was reported to be a magnitude 8.6 earthquake (with a magnitude 8.2 aftershock two hours later).

This was due to the nature of the fault. Rather than a thrust fault, where one block of rock slides up and over another (displacing water and creating a tsunami), this occurred on strike-slip faults, where one block simply slides laterally past another. No earthquake of this magnitude had ever been recorded on a strike-slip fault before. Additionally, the earthquake occurred not at the boundary where two plates meet (as the 2004 earthquake did), but within one of the plates. It was also the largest such “intraplate” quake ever recorded.

Several new papers in the journal Nature this week present detailed analyses of the event. For starters, one of the groups revises the magnitude of the earthquake, bumping it up 8.7—a not insignificant increase on a logarithmic scale, and one that would further secure records for quakes of this type.

Read 10 remaining paragraphs | Comments