Smithsonian Science » geology

Mexico’s Popocatépetl volcano active again

John Barrat — Thu, 03 May 2012 19:24:02 +0000

According to the weekly report of the Smithsonian’s Global Volcanism Program, gas-and-ash plumes rose nearly one mile above the crater of Mexico’s Popocatépetl volcano from April 25 to 27. On April 28 incandescent fragments ejected from the crater and landed on the east flank of the volcano, traveling as far as one-half mile. On May Day, gas-and-steam plumes that occasionally contained low amounts of ash, again rose more than half-a-mile above Popocatépetl’s crater. The volcano’s Alert Level remained at Yellow Phase. This image shows Popocatépetl at night on May 3.

A restless volcano

John Barrat — Thu, 05 Apr 2012 16:55:33 +0000

Restless volcano. This Feb. 10 satellite radar image shows the summit of Alaska’s Cleveland Volcano and a new lava dome within the volcano’s summit crater (which is about 200 meters across). The weekly bulletin of the Smithsonian’s Global Volcanism Program reports elevated surface temperatures consistent with such a lava dome were detected in the crater with infrared satellite imagery on April 4. (Image courtesy AVO/USGS)

Learn about the ash that comes from volcanoes with Dr. Liz Cottrell, a geologist from the National Museum of Natural History

John Barrat — Thu, 08 Mar 2012 18:04:13 +0000

Olivine

John Barrat — Mon, 05 Mar 2012 16:37:01 +0000

Olivine is the most common mineral in Earth’s upper mantle. This olivine crystal from the mid-ocean ridge in the Pacific contains tiny bits of volcanic glass, a sample of the liquid rock the crystal grew from. Smithsonian scientists are interested in the composition of this glass, which includes dissolved water. From the exhibition at the Smithsonian’s National Museum of Natural History exhibition “More Than Meets The Eye.”

Photos reveal recent activity in moon’s crust

John Barrat — Tue, 28 Feb 2012 13:03:20 +0000

New images from NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft show the moon’s crust is being stretched, forming minute valleys in a few small areas on the lunar surface. Scientists propose this geologic activity occurred less than 50 million years ago, which is considered recent compared to the moon’s age of more than 4.5 billion years.

A team of researchers analyzing high-resolution images obtained by the Lunar Reconnaissance Orbiter Camera (LROC) show small, narrow trenches typically much longer than they are wide. This indicates the lunar crust is being pulled apart at these locations. These linear valleys, known as graben, form when the moon’s crust stretches, breaks and drops down along two bounding faults. A handful of these graben systems have been found across the lunar surface.

Thomas Watters of the Smithsonian’s National Air and Space Museum discusses the lunar graben and what they reveal about how the moon evolved. (Credit: NASA’s Goddard Space Flight Center, Dan Gallagher)

“We think the moon is in a general state of global contraction because of cooling of a still hot interior,” said Thomas Watters of the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington, and lead author of a paper on this research appearing in the March issue of the journal Nature Geoscience. “The graben tell us forces acting to shrink the moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the moon cannot be large, or the small graben might never form.”

The weak contraction suggests that the moon, unlike the terrestrial planets, did not completely melt in the very early stages of its evolution. Rather, observations support an alternative view that only the moon’s exterior initially melted forming an ocean of molten rock.

Right: This image shows the largest of the newly detected graben found in highlands of the lunar farside. The broadest graben is about 1,640 feet wide and topography derived from Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) stereo images indicates they are almost 20 meters (almost 66 feet) deep. (Credit: NASA/Goddard/Arizona State University/Smithsonian Institution)

In August 2010, the team used LROC images to identify physical signs of contraction on the lunar surface, in the form of lobe-shaped cliffs known as lobate scarps. The scarps are evidence the moon shrank globally in the geologically recent past and might still be shrinking today. The team saw these scarps widely distributed across the moon and concluded it was shrinking as the interior slowly cooled.

Based on the size of the scarps, it is estimated that the distance between the moon’s center and its surface shank by approximately 300 feet. The graben were an unexpected discovery and the images provide contradictory evidence that the regions of the lunar crust are also being pulled apart.

“This pulling apart tells us the moon is still active,” said Richard Vondrak, LRO Project Scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “LRO gives us a detailed look at that process.”

Left: This image shows the largest of the newly detected graben found in highlands of the lunar farside. The broadest graben is about 500 meters (1,640 feet) wide and topography derived from Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) stereo images indicates they are almost 20 meters (almost 66 feet) deep. (Credit: NASA/Goddard/Arizona State University/Smithsonian Institution)

As the LRO mission progresses and coverage increases, scientists will have a better picture of how common these young graben are and what other types of tectonic features are nearby. The graben systems the team finds may help scientists refine the state of stress in the lunar crust.

“It was a big surprise when I spotted graben in the far side highlands,” said co-author Mark Robinson of the School of Earth and Space Exploration at Arizona State University, principal investigator of LROC. “I immediately targeted the area for high-resolution stereo images so we could create a three-dimensional view of the graben. It’s exciting when you discover something totally unexpected and only about half the lunar surface has been imaged in high resolution. There is much more of the moon to be explored.”

The research was funded by the LRO mission, currently under NASA’s Science Mission Directorate at NASA Headquarters in Washington. LRO is managed by NASA’s Goddard Space Flight Center in Greenbelt, Md. –Source: NASA

Boom and bust cycle of marine biodiversity every 60 million years linked to uplifting of continents

John Barrat — Thu, 23 Feb 2012 18:53:49 +0000

A mysterious cycle of booms and busts in marine biodiversity over the past 500 million years could be tied to a periodic uplifting of the world’s continents, scientists report in the March issue of The Journal of Geology.

The researchers discovered periodic increases in the amount of the isotope strontium-87 found in marine fossils. The timing of these increases corresponds to previously discovered low points in marine biodiversity that occur in the fossil record roughly every 60 million years. Authors of the study are Adrian Melott, professor of physics and astronomy at the University of Kansas, paleobiologist Richard Bambach of the Smithsonian’s National Museum of Natural History, Kenni Petersen of Aarhus University, Denmark, and John McArthur of University College London.

Image right: Yosemite Valley and Half Dome from Glacier Point. (Photo by Jon Sullivan)

Melott, lead author, thinks the periodic extinctions and the increased amounts Sr-87 are linked. “Strontium-87 is produced by radioactive decay of another element, rubidium, which is common in igneous rocks in continental crust,” Melott says. “So, when a lot of this type of rock erodes, a lot more Sr-87 is dumped into the ocean, and its fraction rises compared with another strontium isotope, Sr-86.”

An uplifting of the continents, Melott explains, is the most likely explanation for this type of massive erosion event.

“Continental uplift increases erosion in several ways,” he said. “First, it pushes the continental basement rocks containing rubidium up to where they are exposed to erosive forces. Uplift also creates highlands and mountains where glaciers and freeze-thaw cycles erode rock. The steep slopes cause faster water flow in streams and sheet-wash from rains, which strips off the soil and exposes bedrock. Uplift also elevates the deeper-seated igneous rocks where the Sr-87 is sequestered, permitting it to be exposed, eroded, and put into the ocean.”

The massive continental uplift suggested by the strontium data would also reduce sea depth along the continental shelf where most sea animals live. That loss of habitat due to shallow water, Melott and collaborators say, could be the reason for the periodic mass extinctions and periodic decline in diversity found in the marine fossil record.–Source: University of Chicago Press Journals

A hot new island has just surfaced in the Red Sea. What’s going on? Smithsonian scientists explain.

John Barrat — Wed, 11 Jan 2012 16:45:25 +0000

On Dec. 13, 2011, fishermen from Yemen reported a volcanic eruption in the ocean “popping up red lava that reached 20 to 30 meters high,” in the northern part of the Zubair Island Group in the Red Sea. By Dec. 23, satellites were able to photograph for the first time a new volcanic island topped by a white plume of steam and smoke. What is happening here? To give SmithsonianScience.com readers some insight into just what is happening in the Red Sea, Rob Dennen and Rick Wunderman, volcanologists in the Smithsonian’s Global Volcanism Program, together answer questions about this event.

Image right: This NASA satellite image, acquired Jan. 7, 2012, shows the recent eruption in the Red Sea that has risen completely above water. Click image to enlarge.

Q: Geologically what is going on in these photographs?

A: The new island visible in the satellite photograph is the top of a giant shield volcano located on the rift axis in the Red Sea where the continental plates of Africa and Arabia are pulling apart. As these massive continental plates pull apart volcanic magma forcibly pushes its way up through the fissure and into the Red Sea. This new island emerged above water atop the shield volcano in a cluster of 10 islands called the Zubair Group. Each island represents a different vent area of the volcano and each one, during thousands of years, has been built up from the shield’s summit area, some 325 feet below sea level.

This video shows the new island erupting in the Red Sea.

The “new” volcano, of which you can see the very top, has probably been erupting episodically underwater for thousands of years. While its above-surface dimensions are roughly 1,739 feet east-to-west and 2,329 feet north-to-south we know the larger submerged shield it sits on is about 12.5 miles across—an edifice whose age is unknown, but the Red Sea may have begun spreading apart about 34 million years ago and the shield volcano could thus be tens of millions of years in the making.

Now that this recently active vent has emerged from the sea to make dry land, the eruption has excited media interest and people have begun to hear about it.

Image right: Satellite images showing the Red Sea region where the volcanic island recently appeared before (top) and after.

Q: What are the dangers of being near this newly forming island?

A: It is not implausible that the edifice could fail and cause a tsunami. The aviation community hasn’t reported big plumes of smoke and ash and the maritime community hasn’t reported a lot of floating pumice. The likelihood is that this eruption is kind of local, not too energetic and of little hazard to marine navigation. Lava is probably being spattered at 164 to 325 feet. Most of its activity has been hidden underwater. Now that it has switched from a submarine eruption to an above water eruption, its style of erupting may change….perhaps to some beautiful spray eruptions.

Keep in mind that this whole region has had many volcanic eruptions in the last five years. In 2007, for example, a sudden eruption on the nearby Island Jebel at Tair killed a number of soldiers stationed there. The process of plate tectonics seems to be going on a little faster, at a quickened rate in this area. Why? We don’t know. The general public needs to be reminded that volcanologists are often in the dark about these processes.

Q: What can we expect to see in the next few months from this volcanic island?

A: The supply of magma supplied by the rift axis seems to be a stop-and-go process and repose of these volcanoes is a lot longer than their eruptive phase. Often in the case of submarine volcanoes they wash away in about a year from ocean currents, wind and storms. Also volcanic islands often sink due to a process we don’t understand very well. A lot of volcanoes on the sea floor are flat topped—as they were sinking, it is as if the waves chopped off their tops–gave them a haircut. So this may happen as well.

Other islands in the group clearly have explosion craters of various sizes so it’s possible that before any sinking or washing away occurs, we could see more energetic explosions. Today’s activity may be as energetic as it will get or it may transition to more effusive behavior as the vent is further sheltered from the sea surface.

There’s a lot more up and down to these submarine volcanoes than meets the eye. They may have quite enigmatic lava flows of 70 to 100 miles but the flows are spread out and over time they built up like a stack of pancakes. They are not formed in a central mound like inland volcanoes are.

(Richard Wunderman is managing editor of the Bulletin of the Global Volcanism Network. To read a just-published report on this new volcanic eruption click this link to the Global Volcanism Program Volcanic Activity Reports and click PDF File.)

Satellite images originally published by NASA Earth Observatory.

Q&A: Smithsonian volcanologist Richard Wunderman answers questions about the Aug. 23, East Coast earthquake

John Barrat — Thu, 22 Sep 2011 00:54:51 +0000

Richard Wunderman is managing editor of the Bulletin of the Global Volcanism Network and a geologist in the Division of Mineral Sciences at the Smithsonian’s National Museum of Natural History. Following the earthquake that rumbled across the East Coast of the United States on Aug. 23, Smithsonianscience.org asked Wunderman a few questions about earthquakes and how scientists measure and assess them. He was assisted by interns Claire Hepper and Robert Dennen.

Q. The earthquake that struck the Washington, D.C. area on Tuesday, Aug. 23, was 5.8 magnitude. Why did the earthquake occur? How do scientists assess earthquake size and impact?

A. The Virginia earthquake released energy stored as accumulated stress in the crust along faults along the coastal side of the Appalachian mountains. The resulting shock waves were felt by people into Canada and Georgia. The main areas of damage were strongest near the epicenter, the point on the Earth’s surface above the earthquake, and minor damage in urban areas at distance, such as Washington D.C. located 85 mi. northeast of the epicenter.

Figure right: Generalized geologic map showing the location of the M 5.8 EQ of 23 August 2011. The areas in white are ancient rocks of the Appalachian region that transmit seismic energy efficiently. Some other smaller epicenters also shown. Map taken from blog by C.M. Bailey 2011 (Click image to enlarge).

The cause of the stress is plausibly attributed to factors such as ancient mountain building along the East side of the Appalachian mountains, more recent shifts and adjustments in this region, or from stress developed in more recent times. Virginia’s Division of Geology and Mineral Resources has excellent resources here.

Q. The energy released during the earthquake was stress that had been building up along a fault line in central Virginia for a very long time. Now that this stress has been released, can we relax and not expect another quake for many, many years?

A. Yes, we would assume that along the fault where the earthquake occurred, this might help alleviate another large earthquake there. Trouble is, some of this stress has probably shifted to another area on this or adjacent faults. A complex web of short faults has been mapped in the region.

That being said, the last large earthquake was around 114 years ago, also a magnitude 5.8 quake, so it is seems unlikely that there will be another in the near future. Small earthquakes, which cause little to no damage, have been an almost yearly occurrence in the Virginia seismic area and will likely continue at that recurrence interval.

Q. On Aug. 23, the shaking in Washington, D.C. seemed to last only 20 seconds. Is duration one of the characteristics of an earthquake that is used to measure its magnitude?

A. The size of the earthquake is a potentially confusing topic so I’ll start at a point that everyone can relate to. That is, a general sense of the shaking levels from an earthquake, an estimate called intensity. This measure does not rely on instruments and much in the way of numerical measurements, but addresses the important question of what the shaking actually did.

Yes, the damage could indeed relate to duration of the shaking. And, yes, prolonged duration could spell disaster. Other factors could include the earthquake’s focal depth, its peak accelerations, the kinds of waves generated and their frequencies. Relating to the site, factors include the thickness and kind of crustal material through which the shock waves passed, the local rock and soil types, the slope, and water saturation of the ground. Other critical factors include local rocks and structures such as buildings, bridges, and dams, and how they respond.

Earthquakes can range from not felt and no impact, all the way to leveling large areas, causing secondary effects like substantial tsunamis, landslides, and liquefaction (shaking wet sand, mud, or soils such that it flows, almost like water). The most common intensity scale is the Modified Mercalli scale.

Akin to the intensity scale, the U.S. Geological Survey also employs a system called the “felt magnitude.” This is estimated from personal accounts, and basically asks “how strong did the earthquake feel?” In this estimate, the way an earthquake is perceived by individuals is the measure of the earthquake magnitude, and one person may base their interpretation of the earthquake magnitude on the duration or any other characteristic. The USGS compiled “felt magnitude” for the Aug. 23 Virginia earthquake can be viewed here.

Magnitude, as in an M 5.8 earthquake, represents a scale based on the readings from seismometers and the wave traces we call seismograms. There are various kinds of these magnitude scales (eg. the Richter scale) and the magnitudes are often based on the size of the largest waves received (rather than the duration of the earthquake’s waves).

Figure left: A simplified illustration of earthquake-triggered waves and the resulting seismogram from a site at distance (at left; tracing time on the x-axis and amplitude on the y-axis). The seismogram contains labels indicating the first arrival of waves; the largest amplitude waves in the case shown are waves traveling along the ground surface called Rayleigh waves. The depiction omits the wave paths moving to the left (as well as some other waves). Taken from Stein and Wysession (2003; their online PowerPoint presentation for Chapter 1 of An Introduction to Earthquakes, Seismology, Earthquakes, and Earth Structure).

The distance from the earthquake and its depth are first calculated, and then the instrument readings at various distances from the epicenter are compensated for, and in fact, there are many corrections and assumptions. These values are often computed from multiple stations using computers. They are often refined somewhat, based on new information and various corrections. Comparisons between intensity and magnitude scales are inexact.

Q. Earthquakes by their very nature are relatively short-lived events, over in a few seconds . . . correct? Or do some earthquakes last a long time?

A. Generally the shaking of the Earth as a result of the fracturing along the fault lasts only a few seconds. That said, in a large earthquake, the propagating waves from the fault rupture can shake for minutes, since for one thing, they come from various parts of the fault and also because the waves reflect (bounce around), actually probing the reaches of the entire planet and providing key clues to the various inner parts of the planet (crust, mantle, and two-part core).

Thick sedimentary valleys and basins such as found in many Western USA settings can behave somewhat like jello, and shake much longer (and stronger, that is, with higher amplitude) than the initial passing waves, essentially amplifying the earthquakes intensity.

Weak vibrations triggered by strong earthquakes may cause the entire planet to ring like a bell at amplitudes and frequencies detected instrumentally but not felt by people. This ringing can go on for weeks in the case of a strong earthquake.

Aftershocks, which are the Earth settling and readjusting, can recur sporadically for weeks to more than a decade after an earthquake has occurred, generally diminishing with time in number and strength.

Q. Much of the structural damage to buildings caused by the Aug. 23 earthquake, it seems, occurred to areas that are high up–cracks at the top of the Washington Monument, the spires of the National Cathedral, and the towers and chimneys of the Smithsonian Castle. Why is that?

A. Hold a stiff fishing pole by the handle and oriented vertically. If you give the handle a shake, the rod’s tip will move as the waves arrive, and excursions there will be comparatively large. Structures made of, or faced with stone, offer special challenges, as the ‘building blocks’ they may not hang together during the deformation and shaking.

Image right and above: The Aug.23 earthquake caused damage to the chimneys and other high-up structures on the east end of the Smithsonian Castle. (Photos by Mark Avino and Eric Long)

Q. Is there a way to keep track of how much compression or tension is building up between rock plates on either side of a fault line?

A. There are multiple things than can be measured to keep track of offset along a fault over time. Strain meters measure the amount of strain (the movement or deformation caused by stress) present in the ground. Methods employing GPS or radar look at ground-surface deformation. One of my favorite methods is a simple line of survey monuments across arranged across a fault, repeatedly re-surveyed over time. After an earthquake, features such as roads, fences, and railroad tracks can record earthquake offset. You can see other famous examples here.

(Image left. A photo of an offset fence seen soon after the M 7.8 Great San Francisco earthquake of 1906. The San Andreas fault’s surface trace is drawn as a colored band. This area is now part of Point Reyes National Seashore. Image from Stein and Wysession 2003; online PowerPoint presentation).

Q. Where were you when the earthquake struck and what were your immediate thoughts?

A. I was at my desk in the Smithsonian’s Museum of Natural History on the Mall. Shaking grew to the point where it upset me as some of my geologic colleagues screamed and I heard glassware breaking. No one was hurt. In this commotion I had walked from my desk and braced myself in the office doorway, but the shaking stopped soon after that. As the event had escalated, my thoughts went to the building’s masonry construction and the well known, water-saturated fill in this part of the low-lying Washington, D.C. region. Neither of those thoughts were comforting, but the building withstood the stress without serious damage.

My wife and daughter were in the family car stopped at a traffic light when they felt weird unexplained vibrations. My wife immediately asked my daughter ‘What did daddy do to the car now?’ She attributed the vibration to engine or suspension trouble caused by you-know-who. The announcements of the earthquake saved me from near-certain allegations of car abuse.

500 carats of rough diamonds donated to Natural History Museum

John Barrat — Wed, 17 Aug 2011 16:58:43 +0000

More than 500 carats of rough diamonds were recently donated to the Department of Mineral Sciences of the Smithsonian’s Natural History Museum by Jewlers Mutual Insurance Co. of Neenah, Wis. Although rough diamonds have a limited market value, their value to the museum for research and display is considerable. This donation in particular is unusual in that each diamond in the group is labeled with the location of where it was mined.

Images right and below: Rough diamonds

“It’s very rare to know where some rough diamonds came from because typically, once they come out of the mine, they go to market and are sold,” says Jeffry Post, curator in the Department of Mineral Sciences. “In most cases, diamonds lose any documentary links to their source by the time they reach the market.” This donation will be a great asset to researchers, allowing them to study specimens and knowing where they originated in the Earth.

The larger diamonds in the Jewelers Mutual donation will be added to the diamond exhibition in the Natural History Museum’s Gem and Mineral Hall. The others will be made available for scientific study. Jewelers Mutual originally acquired the diamonds to display in the company’s onsite gallery of gems and minerals in Neenah.

Gale Crater to be landing site for NASA’s Mars Science Laboratory

John Barrat — Fri, 22 Jul 2011 16:29:12 +0000

During a press conference Friday, July 22 at the Smithsonian’s National Air and Space Museum, NASA announced that Gale Crater will be the landing site for the Mars Science Laboratory. Scheduled to launch in late 2011 and arrive at Mars in August 2012, the Mars Science Laboratory is a rover that will assess the planet’s “habitability”—if it ever was, or is today, an environment able to support microbial life.

“Having the right instruments and knowing where to go are equally important,” said John Grant, a Smithsonian geologist and co-chair of the landing site steering committee. “We looked for a site that has water associated with it, materials of interest that are concentrated and preserved and that is accessible so we can get to it. Gale Crater is a good place to explore because there is a mountain of layered materials rising from its floor. Much like chapters in a book, the sediments, minerals and layers in this stack record the story about what Mars was like in the past. The rover will investigate where sediments forming the layers came from and explore how the layers relate to the environments in which they formed.” Grant, who is a researcher in the Center for Earth and Planetary Studies, is also a member of the science team for Mars rovers Spirit and Opportunity.

Image right: Gale Crater is 96 miles in diameter and holds a layered mountain rising about 3 miles above the crater floor. The portion of the crater within the planned landing area north of the mountain has an alluvial fan likely formed by water-carried sediments. The lower layers of the nearby mountain–within driving distance for Curiosity–contain minerals indicating a wet history. (Image NASA/JPL-Caltech/ASU)

The car-sized Mars Science Laboratory, or Curiosity, is scheduled to launch late this year and land in August 2012. The target crater is 96 miles in diameter and holds a mountain rising higher from the crater floor than Mount Rainier rises above Seattle. Gale is about the combined area of Connecticut and Rhode Island. Layering in the mound suggests it is the surviving remnant of an extensive sequence of deposits.

Image left: This artist concept shows NASA’s Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars’ past or present ability to sustain microbial life. In this picture, the rover examines a rock on Mars with a set of tools at the end of the rover’s arm, which extends about 7 feet. (Image NASA/JPL-Caltech)

During a prime mission lasting one Martian year—nearly two Earth years—researchers will use the rover’s tools to study whether the landing region had favorable environmental conditions for supporting microbial life and for preserving clues about whether life ever existed.

In 2006, more than 100 scientists began to consider about 30 potential landing sites during worldwide workshops. Four candidates were selected in 2008. An abundance of targeted images enabled thorough analysis of the safety concerns and scientific attractions of each site. A team of senior NASA science officials then conducted a detailed review and unanimously agreed to move forward with the MSL Science Team’s recommendation. The team is comprised of a host of principal and co-investigators on the project.

NASA Video: Animation of the Mars Science Laboratory from entry, descent and landing phase to surface operation.

Curiosity is about twice as long and more than five times as heavy as any previous Mars rover. Its 10 science instruments include two for ingesting and analyzing samples of powdered rock that the rover’s robotic arm collects. A radioisotope power source will provide heat and electric power to the rover. A rocket-powered sky crane suspending Curiosity on tethers will lower the rover directly to the Martian surface.

The rover and other spacecraft components are being assembled and are undergoing final testing. The mission is targeted to launch from Cape Canaveral Air Force Station in Florida between Nov. 25 and Dec. 18. NASA’s Jet Propulsion Laboratory in Pasadena manages the mission for the agency’s Science Mission Directorate in Washington. JPL is a division of Caltech.