Supervolcanoes on Mars!

The process that created the crater-rich region of Mars known as Arabia Terra has been determined – and they are not even craters at all!   They are calderas formed from collapsed volcanoes, containing large deposits of volcanic rock and ash debris.  The volcanic field, located in the equatorial region of the planet, consist of dozens of crater-like features, whose largest measures about 35 miles long and 55 miles wide (that’s bigger than Rhode Island).

Scientists associated with NASA and the Planetary Science Institute have used a variety of techniques to analyze the surficial geology from multiple Martian spacecraft. The Mars Express satellite used lasers to produce topographic maps and thermal images while high-resolution photographs were taken by the Mars Reconnaissance Orbiter and Mars Global Surveyor.  The science team determined that only ancient supervolcanoes could produce the vast quantities of volcanic rocks and ash debris found in the area.  The so-called ‘plain-style caldera complexes,’ similar to the Yellowstone caldera and Snake River Plain on Earth, are characterized by collapsed, low craters and plain-like lava flows.  The calderas themselves feature rings of fault scarps caused by the collapse of the structure as it sinks into the now-empty magma chamber; the structures are identical to structures found in collapsed calderas on earth, such as in Yellowstone and Long Valley, CA. During some eruptions, the empty magma chamber left behind acts like a giant sinkhole, collapsing under its own weight; it’s similar to trying to stand on an empty cardboard box versus a full one. These supervolcanoes represent a new form of Martian volcanism not previously identified anywhere else on the planet.

False color map of Martian topography. Cool colors indicate low elevations, while warm colors indicate high elevations. Arabia Terra, indicated by the box near the middle of the image, is home to Mars' newly identified supervolcanoes. Image modified from NASA.

Mars is no stranger to volcanism.  It is most known for its shield volcanoes like Olympus Mons, the largest volcano in the solar system, located in the Tharsis province.  These large volcanoes are similar in morphology to the volcanoes found in Hawaii, with gentle slopes that spread over hundreds of miles. Also like Hawaii, they would have erupted effusively, not producing the ash columns like those at Mt. St. Helens.  These eruptions were caused by magma chambers deep beneath the planet’s surface and occurred over long periods of time. 

In contrast, the newly identified Martian supervolcanoes would have had magma chambers closer to the surface and erupted explosively from several vents.  Supervolcanoes erupt massive amounts of material;  on Earth, a volcano must eject at least 1000 km³ of volcanic material (the equivalent to 400 Olympic swimming pools) to be considered a supervolcano.  There are dozens of known explosive supereruptions on Earth during the course of geologic time, the largest being the La Garita Caldera eruption in Colorado, which erupted 5,000 km³ of material.  Calculations based on satellite data indicate that the craters at Arabia Terra erupted almost twice as much material as the La Garita Caldera and thousands times more material than other Martian volcanoes.

The question remains: Why would supervolcanoes erupt at Arabia Terra and not anywhere else on the planet?  The Arabia Terra caldera is one of the oldest known features on the planet.  To the north of the region are fields of younger shield volcanoes; to the south are fields of crater impacts from meteorites that have decimated the landscape.  As such, the Arabia Terra region is one of the few regions of Mars where such features would be preserved and not destroyed or covered by other rocks. The early Martian surface may have been covered by these large supervolcanoes in the past, with only those at Arabia Terra still apparent.  Additionally, volatiles often need to be added to the magma to produce large supereruptions – volatiles like water! These supervolcanoes could be an indicator of higher water content on Mars billions of years ago. 

The discovery of supervolcanoes on Mars is an exciting discovery for not only planetary geologists but for terrestrial volcanologists as well.  Further study of these large eruption deposits could give some insight to the conditions surrounding the supereruptions on Earth, like those from Yellowstone.

Check out the original paper at: Michalski, J.R., and Bleacher, J.E. (2013).  “Supervolcanoes within an achient volcanic province in Arabia Terra, Mars,” Nature 502 pg 47-52

Lasers Finding Faults in Central Idaho

Idaho, with a box around the Sawtooth Mountains where the fault was recently found. Future movement on the fault will be felt in Boise, the largest city in Idaho. Figure made using TopoCreator.com.

ISU geology professor and department chair Glenn Thackray led a team that recently discovered a previously unknown earthquake-producing fault in the Sawtooth Mountain Range in central Idaho, USA. The fault is about 40 miles long and thought to be comprised of two segments.  Capable of producing a magnitude 7.0 earthquake (similar to the 1989 San Francisco Earthquake), it was last active 4000 and 7000 years ago. If the fault ruptured again, it could cause major damage to the Sawtooth National Recreation Area and Sun Valley Ski Resort. A major earthquake could produce moderate shaking in the Wood River Valley (pop. 22,000), located 25 miles south, and the Boise metropolitan area (pop. 617,000), located 65 miles southwest.

The Sawtooth Mountain Fault. Aerial photo one left shows vegetation that prevented previous identification of the fault. The fault is highlighted in hot pink in the shaded relief map on the right. Note: images not at exact same scale. Modified from Thackray et al. (2013).

The geoscientists from Idaho State University mapped the fault using Light Detection and Ranging (LiDAR) technology.  LiDAR, a light-based remote sensing method, is similar to radar or sonar; it measures the time it takes for a light shined at a surface to return to its source, calculating the distance from the surface to the receiver using the speed of light.  Thousands of data points are combined to create a detailed map of the earth’s surface.  LiDAR is ideal for studying faults that are difficult to detect using traditional mapping techniques because it allows for remote access to inaccessible terrain. In this study, data was collected by an airplane equipped with a LiDAR scanner that allowed safe and rapid data collection in a relatively remote part of Idaho.

One of the challenges that comes with using LiDAR is that it records trees, bushes, and other vegetation as well as the earth’s surface below.   While vegetation mapping is perfect for some applications, including mapping fuel loads for forest fires, it masks the rock surfaces that are indicative of faults.   This study shows that the current software for removing vegetation from the LiDAR images is precise enough to reveal faults in the surface of the earth if the resolution of data is high enough – in this case, point spacing of less than a yard was sufficient to find the previously unknown fault through the dense forest growing over it.

Mapping via LiDAR through vegetation has major implications for studying faults and other landforms.  There are many places where rocks are not exposed or are only exposed in small places; geologists can now map these zones with more detail thanks to LiDAR, including finding more unknown faults like the one in the Sawtooth Mountains.  

Original article: Thackray, Glenn D., David W. Rodgers, and David Streutker. "Holocene scarp on the Sawtooth fault, central Idaho, USA, documented through lidar topographic analysis." Geology 41.6 (2013): 639-642.

Mystery of the Whorl Tooth Shark of Idaho Revealed

Whorl teeth fossil: all that we have left of Helicoprion. CREDIT: Tapanila et al. (2013)

The spiral-shaped whorl of the ancient shark Helicoprion has left paleontologists questioning its functionality for over a century.  First described in 1899, Helicoprion, which is more closely related to the now extinct ratfish, inhabited the oceans from the Pennsylvanian period (310 million years ago) through the Early Triassic period (250 million years ago). Because only the whorl is preserved, scientists and artists have gotten very creative in trying to figure out what this mysterious critter actually looked like; some the ideas, shown below, include placement of the whorl on the tail, fins, or face.

Reconstructions of Helicoprion with different whorl morphology with (l) being the most recent reconstruction. CREDIT: RAY TROLL

Using CT scans, a team of scientists led by Dr. Leif Tapanila of Idaho State University’s Department of Geosciences have discovered the function of the buzz tooth whorl.  The CT scan of a Helicoprion whorl known as IMHN 37899 or ‘Idaho 4’ revealed the cartilage structure of its head, including the upper jaw, lower jaw, and a piece of cartilage that extends from the lower jaw and braces against the base of the outermost whorl. The whorl itself is a singular fused structure of the lower jaw that takes up the entire mandibular arch. 

Previous reconstructions suggested that the whorl extended beyond lower jaw and curled underneath the chin, whereas this reconstruction suggests that the whorl grew inside of the lower jaw. The whorl grows continually throughout the shark’s life with each new tooth pushing the rest of the teeth forward in a curved direction, creating the iconic spiral.  Helicoprion’s teeth were pushed backwards when the lower jaw closed, creating a slicing mechanism that cut food and forced it into the back of the mouth. 

Interested in learning more about Helicoprion? The Idaho Museum of Natural History in Pocatello, ID is running a special exhibition until the end of 2013, featuring the artwork of Ray Troll.  Tickets are $5 for adults and $1 for children K-12.

Original article: Tapanila, L., Pruitt, J., Pradel, A., Wilga, C., Ramsay, J., Schlander, R., and Didier, D., "Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion." Biology letters 9, no. 2 (2013).