The U.S. Geological Survey recently awarded nearly $1 million to four university programs across the country, through the National Competitive Grants Program.
Proposals from Purdue University, University of Iowa, University of Maryland, and the University of Nebraska won the grants this year.
Purdue University’s project will address the need to improve the nation’s water supply through the evaluation of what factors limit adoption of urban stormwater conservation practices. The project goal is to improve water quality planning and implementation management practices.
The University of Iowa will develop statistical models to describe the relationship between inland flooding and North Atlantic tropical storms. This knowledge is instrumental in identifying and characterizing areas at risk from flooding and for developing a model to determine economic impacts of such events.
University of Maryland’s objective is to characterize the number and concentration of gestagens in tributaries of the Chesapeake Bay and to document the exposure effects of gestagens on the reproductive health of the fathead minnow. Because fish are key indicators of the effects of steroid hormones and other emerging contaminants in water, they can reveal critical insights for understanding the quality of the Nation’s water supply.
University of Nebraska’s research will develop models to predict how soluble uranium is transported and how it can be remediated or reduced. Soluble uranium is a recognized contaminant in public ground water supplies in various regions throughout the United States. It can appear in drinking water in both urban and rural communities, which has led to human health concerns including kidney failure and cancer risk. How this occurs is poorly documented.
The goals of the National Competitive Grants program are to promote collaboration between USGS and university scientists in research on significant national and regional water resources issues; promote the dissemination and results of the research funded under this program; and assist in the training of scientists in water resources.
The federal funding for this program is required to be matched with non-federal dollars each year. Any investigator at an accredited institution of higher learning in the United States is eligible to apply for a grant through a Water Research Institute or Center established under the provisions of the Water Resources Research Act of 1984.
A new USGS report presents a comprehensive assessment of mercury contamination in streams across the United States. It highlights the importance of environmental processes, monitoring, and control strategies for understanding and reducing stream mercury levels.
Methylmercury concentrations in fish exceed the human health criterion in about one in four U.S. streams.
Mercury contamination of fish is the primary cause of fish consumption advisories, which currently exist in every state in the nation. Mercury can travel long distances in the atmosphere and be deposited in watersheds, thus contaminating fish even in areas with no obvious source of mercury pollution.
“Understanding the source of mercury, and how mercury is transported and transformed within stream ecosystems, can help water resource managers identify which watersheds are most vulnerable to mercury contamination. They can then prioritize monitoring and management actions,” said William Werkheiser, USGS Associate Director for Water.
Some of the highest fish mercury levels were found in southeastern U.S. streams draining forested watersheds containing abundant wetlands.
Wetlands provide ideal conditions for atmospherically deposited mercury to be converted to methlymercury — which enters the aquatic food web and ultimately bioaccumulates in fish, especially top predator game fish such as largemouth bass. Thus, wetland construction or restoration (for example, to improve habitat or to filter nutrients and sediment) should balance the potential for increased methylmercury production against the anticipated ecological and water-quality benefits of the wetlands.
Elevated mercury levels also were noted in areas of the western U.S. affected by historical gold and mercury mining.
Fish mercury levels were lowest in urban streams, despite an abundance of sources of inorganic mercury. This occurs because urban streams lack conditions, such as wetlands, that are conducive to production and bioaccumulation of methylmercury.
In contrast to other environmental contaminants, mercury emission reduction strategies need to consider global mercury sources in addition to domestic sources. Reductions in domestic mercury emissions are likely to result in lower mercury levels in fish in the eastern U.S., where domestic emissions contribute a large portion of atmospherically deposited mercury. In contrast, emission controls will provide smaller benefits in the western U.S., where reduced domestic emissions may be offset by increased emissions from Asia.
Atmospheric mercury emissions from municipal and medical waste incineration, metallurgical processes, and other sources have been reduced in the U.S. by more than 60 percent since 1990. Mercury concentrations in lake sediment, fish tissue, and precipitation have decreased in some areas of the U.S. during recent decades, coincident with mercury reduction legislation. The development of a national monitoring approach will be critical to track the effectiveness of future management actions.
PORTLAND, Ore. — Amphibians, including threatened and endangered species like the Oregon Spotted Frog, may benefit from a recent study that highlights the use of promising tools that can assess the risk of disease exposure. With global biodiversity decreasing, it has become important for scientists to find new and innovative tools to quickly assess how environmental hazards affect wildlife, especially those that are threatened or endangered.
“By sampling water for amphibian chytrid fungus, rather than sampling amphibians directly, we can detect the pathogen with as few as four samples,” says U.S. Geological Survey researcher Tara Chestnut.
This information is vital to researchers and resource managers, alike, by providing early detection of potential problems that may require immediate conservation efforts or further detailed investigation. Of all species, amphibians (e.g. frogs, toads, salamanders, and newts) appear especially vulnerable to environmental hazards, with up to 41 percent considered threatened worldwide. One potentially lethal threat is the chytrid fungus, Batrachochytrium dendrobatidis. The amphibian chytrid fungus causes the disease chytridiomycosis, which is linked to many of the observed amphibian population declines and extinctions globally.
For this study, scientists coupled sophisticated molecular tools with advanced statistics to evaluate whether the amphibian chytrid fungus occupied ponds and wetlands. First, they used DNA extracted from water samples to test for the presence and abundance of the amphibian chytrid fungus. Then they used an occupancy modeling method to estimate the chance of a false-negative result, or the likelihood of not detecting the pathogen when it was actually present. The study found chytrid fungus in approximately 61 percent of sampled ponds and wetlands. The fungus was present year round at the long-term monitoring site, but its density was highest in the spring. Beside seasonal variability, elevation also played a role in the presence of the fungus. Chytrid fungus was more common in amphibian breeding habitats at lower elevations than those habitats at higher elevations.
Among the benefits of these tools, scientists have been able to improve survey protocols, which increases the chances of detecting the amphibian chytrid fungus in the environment, while reducing the risk of a false-negative. More importantly, these tools are not limited to only studying the amphibian chytrid fungus. These same methods can be modified to quickly and applied to other aquatic diseases that pose risks to the health of wildlife and humans alike.
“When we study the ecology of pathogens by sampling the environment, conservation efforts can be more informed and focused to meet the management goals and objectives for threatened and endangered species, and common species,” says Chesnut.
Pharmaceuticals from Treated Municipal Wastewater Can Contaminate Shallow Groundwater Following Release to Streams
Pharmaceuticals and other contaminants from treated municipal wastewater can travel into shallow groundwater following their release to streams, according to a recent USGS study. The research was conducted at Fourmile Creek, a small, wastewater-dominated stream near Des Moines, Iowa.
“Water level measurements obtained during this study clearly show that stream levels drive daily trends in groundwater levels. Combined with the detection of pharmaceuticals in groundwater collected several meters away from the stream, these results demonstrate that addition of wastewater to this stream results in unintentional, directed transport of pharmaceuticals into shallow groundwater,” said Paul Bradley, the study’s lead author.
Samples for the study were taken from Fourmile Creek during the months of October and December of 2012. In October, the wastewater made up about 99 percent of the stream’s flow, whereas in December, the wastewater made up about 71 percent of the stream’s flow. During both months, Fourmile Creek experienced persistent dry conditions.
Pharmaceuticals and other wastewater contaminants are most likely to contaminate adjacent shallow groundwater systems during dry conditions when wastewater contributes the greatest proportion to streamflow.
The samples from the stream and groundwater were analyzed for 110 pharmaceutical compounds, as well as other chemicals like personal care products and hormones. These compounds are able to move into the groundwater systems because they remain dissolved in the water, rather than attaching themselves to the sediments that filter other chemicals out of the water as it moves from the stream into adjacent groundwater. There were no sources of these pharmaceuticals to groundwater in the study reach other than municipal wastewater in the stream.
This study found that 48 and 61 different pharmaceuticals were present in the stream downstream of the wastewater discharge point during the two periods of study, with concentrations as high as 7,810 parts-per-trillion (specifically the chemical metformin, an anti-diabetic pharmaceutical). Correspondingly, between 7 and 18 pharmaceuticals were present in groundwater at a distance of about 65 feet (20 meters) from the stream bank, with concentrations as high as 87 parts-per-trillion (specifically fexofenadine, an antihistamine pharmaceutical).
“This research has important implications for the application of bank filtration for indirect water reuse,” said Bradley. Bank filtration is the engineered movement of water between surface water bodies and wells located a short distance away on the streambank. Bank filtration is routinely used to pretreat surface-water for drinking water supply (raw surface water moves from the stream to a shallow groundwater extraction well), or as a final polishing step for the release of treated wastewater (treated wastewater moves from infiltration wells or lagoons through the bank to the stream).
This study is part of a long-term effort to determine the fate and effects of contaminants of emerging concern and to provide water-resource managers with objective information that assists in the development of effective water management practices.
The paper is entitled “Riverbank filtration potential of pharmaceuticals in a wastewater-impacted stream” and has been published in Environmental Pollution. More information on this study and other studies on contaminants of emerging concern can be found here. To learn more about USGS environmental health science, please visit the USGS Environmental Health website and sign up for our GeoHealth Newsletter or our Environmental Health Headlines.
The sixth of a series of handbooks on technologies for management of metal mining influenced water is now available online from the Society of Mining, Metallurgy & Exploration Inc.
“This volume was prepared through the Acid Drainage Technology Initiative–Metal Mining Sector (ADTI-MMS), which includes USGS mine drainage expertise, other federal and state agencies, industry, and academia, to develop a handbook with an approach for environmental sampling and characterization throughout the mine life cycle,” said Kathy Smith, U.S. Geological Survey research geologist and co-editor of the new publication.
This handbook supplements and enhances current environmental mine sampling and monitoring literature and provides an awareness of the specialized approach necessary for environmental sampling and monitoring at mining sites. It differs from most information sources by providing an approach to address mining influenced water and other sampling media throughout the mine life cycle.
Sampling and Monitoring for the Mine Life Cycle is organized into a main text and six appendices, including an appendix containing technical summaries written by subject-matter experts that describes various analytical, measurement and collection procedures. Sidebars and illustrations are included to provide additional detail about important concepts, to present examples and brief case studies and to suggest resources for further information. Extensive references are included.
For more information about USGS minerals research, please visit the website.
Thomas Wright ( Phone: 301-365-2287 );
Professional Paper 1806: Two Hundred Years of Magma Transport and Storage at Kīlauea Volcano, Hawaiʻi, 1790–2008
ISLAND OF HAWAIʻI, Hawaiʻi — A new book that summarizes the Kīlauea magma system is now available online, with printed copies to follow soon. The U.S. Geological Survey monograph summarizes the evolution of the internal plumbing of Kīlauea Volcano on the Island of Hawaiʻi from the first documented eruption in 1790 to the explosive eruption of March 2008 in Halemaʻumaʻu Crater.
For the period before the founding of the Hawaiian Volcano Observatory in 1912, the authors rely on written observations of eruptive activity, earthquake swarms, and periodic draining of magma from the lava lake present in Kīlauea Caldera by missionaries and visiting scientists. After 1912 the written observations were supplemented by continuous measurement of tilting of the ground at Kīlauea’s summit and by a continuous instrumental record of earthquakes, both measurements made during 1912–56 by a single pendulum seismometer housed on the northeast edge of Kīlauea’s summit. Scientific interpretations become more robust following the installation of seismic and deformation networks in the 1960s. A major advance in the 1990s was the ability to continuously record and telemeter ground deformation to allow its precise correlation with seismic activity before and after eruptions, intrusions, and large earthquakes.
In Kīlauea’s 200-year history, USGS scientists and authors of the new volume, Thomas Wright and Fred Klein, identify three regions of the volcano in which magma is stored and supplied from below. Source 1 is at 1-km depth or less beneath Kīlauea’s summit and fed Kīlauea’s summit lava lakes throughout most of the 19th century and again from 1907 to 1924. Source 1 was used up in the series of small Halemaʻumaʻu eruptions following the end of lava-lake activity in the summit collapse of 1924. Source 2 is the magma reservoir at a depth of 2–6 km beneath Kīlauea’s summit that has been imaged by seismic and deformation measurements beginning in the 1960s. This source was first identified in the summit collapses of 1922 and 1924. Source 3 is a diffuse volume of magma-permeated rock between 5 and 11 km depth beneath the east rift zone and above the near-horizontal fault at the base of the Kīlauea edifice.
Kīlauea’s history can be considered in cycles of equilibrium, crisis, and recovery. The approach of a crisis is driven by a magma supply rate that greatly exceeds the capacity of the plumbing to deliver magma to the surface. Crises can be anticipated by inflation measured at Kīlauea’s summit coupled with an increase in overall seismicity, particularly manifest by intrusion and eruption in the southwest sector of the volcano. Unfortunately the nature of the crisis—for example, a large earthquake, new eruption, or edifice-changing intrusion—cannot be specified ahead of time. The authors conclude that Kīlauea’s cycles are controlled by nonlinear dynamics, which underscores the difficulty in predicting eruptions and earthquakes.
Highlights of interpretations for the period prior to 1952 are:
• Prior to and including 1924, major subsidence events include draining of the deep magma system identified beneath Kīlauea’s East Rift Zone. 1924 is the last such occurrence.
• A massive intrusion on the lower east rift zone preceding the 1924 phreatic activity at Kīlauea’s summit stabilized the south flank and the present magmatic system.
• The 1952 eruption was preceded by deep earthquakes associated with the magma supply path from the mantle resulting in the beginning of a steady increase in magma supply rate extending to 2008. A large earthquake swarm on the offshore part of Kīlauea’s south flank in the months before the 1952 eruption ushered in the modern era of seaward spreading.
Interpretations in the post-1952 period are based on connecting events over a far longer time period than the duration of any one person’s tenure on the USGS Hawaiian Volcano Observatory staff.
• Kīlauea’s shallow magma system is envisioned as a small molten core surrounded by a partially molten matrix able to record both short- and long-period seismicity.
• Magma coming from the mantle enters the rift zone before it reaches the molten core and appears in rift eruptions before it is seen as a summit eruption.
• Earthquake swarms beneath Kīlauea’s south flank precede as well as succeed shallow intrusions, supporting the modern idea of deep magma pressure being exerted from beneath the East Rift Zone.
• Prior to the M7 south flank earthquake on November 29, 1975 south flank spreading was driven by Kīlauea’s magma supply. Following the earthquake the spreading rate was decoupled from the still increasing magma supply rate.
• The seismic signatures of “suspected deep intrusions” in the monograph are equated with similar signatures that characterize “slow-slip” or “silent” earthquakes. The occurrence of such events is inferred to extend as far back as the 1960s well before continuous geodetic monitoring could identify correlated spreading steps.
• Major changes in Kīlauea’s behavior, such as ends of long eruptions, large south flank earthquakes or changes in eruptive style are anticipated by increased seismic activity on the southwest side of the volcano. The nature of the coming event is not specified, which emphasizes the uncertainties in eruption and earthquake forecasting, even in an increasingly well-monitored, but yet imperfectly understood volcano.
Citation: Wright, T.L., and Klein, F.W., 2014, “Two hundred years of magma transport and storage at Kīlauea Volcano, Hawai'i, 1790-2008,” U.S. Geological Survey Professional Paper 1806, 240 p., plus 8 digital appendixes.
Appendices include yearly time-series seismic plots and map plots for all intrusion-related earthquake swarms covered in the text. Earthquakes are color-coded to indicate those preceding, during, and following the intrusion.
LEETOWN, W.Va. -- New USGS-led research suggests that fish exposed to estrogenic endocrine-disrupting chemicals may have increased susceptibility to infectious disease.
Exposure to endocrine-disrupting chemicals can affect the reproductive system and cause the development of characteristics of the opposite sex, such as eggs in the testes of male fish. Wild- caught fish affected by endocrine-disrupting chemicals have been found in locations across the county. Estrogenic endocrine-disrupting chemicals are derived from a variety of sources from natural estrogens to synthetic pharmaceuticals and agrochemicals that enter the waterways.
In this study, researchers discovered that cellular receptors for estrogen were present in cells of the channel catfish immune system, which alters the immune system response. These cellular receptors are similar to “on-off switches” that require a lock and key for activation. The study looked at channel catfish because of their well-researched leukocyte cell lines. Leukocytes are immune system cells involved in defending the body against infectious disease and foreign invaders.
Estrogens have been shown to modify immune system responses in mammals and a diverse group of ray-finned fishes that include tunas, halibut, herring and catfish. Most fish species are members of this group, called teleosts. Prior to this research few studies looked at how estrogen receptors in fish leukocytes function.
The study also marks the first time the dynamics of estrogen receptor gene behavior has been evaluated in activated immune cells. Immune cells are either activated or not, much like a dimmable light, there are degrees of activation. The researchers found that all cells of the immune system are not likely to be equally affected.
“We found that B-cells that produce antibodies, T-cells that regulate and coordinate immune responses and destroy virus-infected cells, and macrophages that gobble up invaders, have different arrays of estrogen receptors,” said lead author, USGS research biologist Luke Iwanowicz. “It is likely that these cells are instructed by estrogens differently.”
Iwanowicz noted that this work moves researchers one step closer to better understanding the consequences of exposure to estrogenic substances on the immune function in fish. “This new research not only means that endocrine disruptors may make fish more prone to disease, but it also provides the context and baseline data to enhance our ability to conduct similar work in wild-caught fishes and investigate relationships between disease in the aquatic environments and endocrine disruptors.”
Based on these findings, future research would explore age-related differences as well as seasonal differences in fish and estrogenic endocrine-disrupting chemical exposure.
The journal article, “Channel catfish (Ictalurus punctatus) leukocytes express estrogen receptor isoforms ERα and ERβ2 and are functionally modulated by estrogens,” by L.R. Iwanowicz, J.L. Stafford, R. Patino, E. Bengten, N.W. Millerand V.S. Blazer, is available online in Fish & Shellfish Immunology.
Jon Campbell ( Phone: 703-648-4180 );
USGS collects a wide range of hydrologic data, assures the quality of these data, and makes historical and continuing records of the nation’s water resources freely available in national databases. USGS scientists have recently published two separate papers that provide national overviews of the status of USGS water resources information in the context of historical and technical developments in the last half-century.
Robert M. Hirsch and Gary T. Fisher (retired) point out in “Past, Present, and Future of Water Data Delivery from the U.S. Geological Survey” that USGS innovations, aided by rapidly improving technology, have enabled a transition in recent years from paper reports to online reports and from daily data to instantaneous data. An increasing emphasis on national and international data standards and web services makes it possible for users in the water management and research communities to quickly and easily import USGS water data into the operational and scientific software tools that they use. Further, distributing water data with applications on new mobile platforms brings value to new and nontraditional consumers of hydrologic information.
Writing in the May 2014 edition of Water Resources Impact, USGS Chief Scientist for Water Jerad D. Bales reviews (PDF) 1974 predictions of how water data would be collected in the future and notes how those predictions have been fulfilled or altered. He also describes factors, both technical and otherwise, affecting changes in water-resources data collection and management, as well as future challenges for water data collection.
Robert M. Hirsch and Gary T. Fisher. “Past, Present, and Future of Water Data Delivery from the U.S. Geological Survey” in Journal of Contemporary Water Research & Education, Universities Council on Water Resources, Issue 153, April 2014, pp. 4-15.
Jerad D. Bales. “Progress in Data Collection and Dissemination in Water Resources – 1974-2014” (PDF) in Water Resources IMPACT, May 2014, v. 16, no. 3, pp. 18-23.
Pharmaceuticals, personal-care products, and other contaminants are widespread in water that has passed through landfill waste. The samples of this liquid, also known as leachate, were collected from within each of the studied landfills. This study by the U.S. Geological Survey is the first national assessment of these chemicals of emerging concern in landfill leachate in the United States.
USGS scientists collected leachate from 19 active landfills and analyzed it for 202 chemicals across a wide range of uses, including pharmaceuticals, hygiene products, home-use chemicals, pesticides, plastics, etc. Of those 202 chemicals, 129 were found.
“This represents the first step in USGS efforts to quantify the contribution of contaminants of emerging concern in leachate from active landfills to the environment,” said Dana Kolpin, USGS, the research team leader. “Follow-up research will examine contaminant concentrations in treated and untreated leachate that is released to the environment.”
Of the chemicals found, concentrations varied. Steroid hormone concentrations generally ranged from 1 to 100’s nanograms per liter (ng/L, or parts per trillion); prescription and nonprescription pharmaceutical concentrations generally ranged from 100 to 10,000’s ng/L; and home-use and industrial chemical concentrations generally ranged from 1,000 to 1,000,000’s ng/L.
The 19 active landfills are located all across the United States and represent a snapshot of the various conditions that affect landfills.
“As expected, we found more chemicals and generally higher concentrations in landfills from wetter regions compared to those from drier regions,” said USGS scientist Jason Masoner, the primary author of this paper. “Overall, this study provides a better understanding of sources of contaminants of emerging concern in landfills.”
Chemicals commonly detected include:
- bisphenol A—detected in 95 percent of samples, used to make plastics and resins
- cotinine—detected in 95 percent of samples, a chemical formed from nicotine
- N,N-diethyltoluamide—detected in 95 percent of samples, also known as DEET
- lidocaine—detected in 89 percent of samples, used as anti-itching and local anesthetic
- camphor—detected in 84 percent of samples, used in a variety of medicines and lotions
This study is part of a long-term effort to determine the fate and effects of contaminants of emerging concern and to provide water-resource managers with objective information that assists in the development of effective water management practices.
The paper is entitled “Contaminants of Emerging Concern in Fresh Leachate from Landfills in the Conterminous United States” and has been published in Environmental Science: Processes & Impacts. More information on this study and other studies on contaminants of emerging concern can be found here. To learn more about USGS environmental health science, please visit the USGS Environmental Health website and sign up for our GeoHealth Newsletter or our Environmental Health Headlines.
Robin Fergason ( Phone: 928-556-7034 );
TEMPE, Ariz. – A heat-sensing camera designed at Arizona State University has provided data to create the most detailed global map yet of Martian surface properties. The map uses data from the Thermal Emission Imaging System (THEMIS), a nine-band visual and infrared camera on NASA’s Mars Odyssey orbiter. An online version of the map optimized for scientific researchers is also available.
The new Mars map was developed by Robin Fergason of the U.S. Geological Survey Astrogeology Science Center in Flagstaff, Arizona, in collaboration with researchers at ASU's Mars Space Flight Facility. The work reflects the close ties between space exploration efforts at Arizona universities and the USGS.
"We used more than 20,000 THEMIS nighttime temperature images to generate the highest resolution surface property map of Mars ever created," said Fergason, who earned her Ph.D. degree at ASU in 2006. "Now these data are freely available to researchers and the public alike."
Surface properties tell geologists about the physical nature of a planet or moon's surface. Is a particular area coated with dust, and if so, how thick is it likely to be? Where are the outcrops of bedrock? How loose are the sediments that fill this crater or that valley? A map of surface properties lets scientists begin to answer such questions.
The new map uses nighttime temperature images to derive the "thermal inertia" for football field-sized areas of Mars. Thermal inertia is a calculated value that represents how fast a surface heats up and cools off. As night follows day on Mars, loose fine-grain materials such as sand and dust change temperature quickly and thus have low values of thermal inertia. Bedrock has a high thermal inertia because it cools off slowly at night and warms up slowly by day.
"Darker areas in the map have a lower thermal inertia and likely contain fine particles, such as dust, silt or fine sand," said Fergason. “Brighter regions have higher thermal inertia surfaces, consisting perhaps of coarser sand, surface crusts, rock fragments, bedrock or combinations of these materials.”
The designer and principal investigator for the THEMIS camera is Philip Christensen, Regents' Professor of Geological Sciences in the School of Earth and Space Exploration, part of the College of Liberal Arts and Sciences on the Tempe campus. Four years ago, Christensen and ASU researchers used daytime THEMIS images to create a global Mars map depicting the planet's landforms, such as craters, volcanoes, outflow channels, landslides, lava flows and other features.
"A tremendous amount of effort has gone into this great global product, which will serve engineers, scientists and the public for many years to come," Christensen said. "This map provides data not previously available and will enable regional and global studies of surface properties. I'm eager to use it to discover new insights into the recent surface history of Mars."
Fergason noted that there's a practical side, too.
"NASA used THEMIS images to find safe landing sites for the Mars Exploration Rovers in 2004 and Curiosity, the Mars Science Laboratory rover, in 2012," she said. "THEMIS images are now helping to select a landing site for NASA's next Mars rover in 2020."
Jennifer LaVista ( Phone: 303-202-4764 );
Seasonal carbon dioxide frost, not liquid water, is the main driver in forming gullies on Mars today, according to a recent U.S. Geological Survey study that relied on NASA’s Mars Reconnaissance Orbiter’s (MRO) repeated high-resolution observations.
Martian gullies are landforms typically consisting of steep channels, usually having a recessed head, that feed into a fan of material deposited at the bottom. The discovery of active gullies was first reported in 2000, which generated excitement due to consideration that they might result from action of liquid water. Mars has water vapor and plenty of water ice, but liquid water, a necessity for all known life, has not been confirmed on modern Mars. The new report, published in the journal Icarus, is available online.
"As recently as five years ago, I thought the gullies on Mars indicated activity of liquid water," said USGS scientist Colin Dundas, lead author of the new report. "We were able to get many more observations, and as we started to see more activity and pin down the timing of gully formation and change, we saw that the activity is in winter."
A smaller type of seasonal flow seen on some slopes on Mars may involve liquid water, but is yet to be determined. These flows are called recurring slope lineae (RSL), and are sometimes found within small channels but not systematically associated with larger gullies.
Dundas and collaborators used the High Resolution Imaging Science Experiment (HiRISE) camera on MRO to examine each of 356 Martian sites with gullies at least twice, beginning in 2006. Thirty-eight of the sites showed activity, such as cutting a new channel segment or adding material to the apron-shaped deposit at the downhill end of a gully. Wherever the timing of before-and-after observations enabled determining the season of gully activity, it was a time too cold for the possibility of melting water-ice, but consistent with seasonal carbon dioxide frost.
"RSL and mass movements in Martian gullies are two distinct types of slope activity,” said Dundas “It's not hard to tell them apart in HiRISE images. The classic Martian gullies are much larger than RSL. Many of them are more the size that you'd call ravines on Earth."
Frozen carbon dioxide, commonly called dry ice, does not exist naturally on Earth, but it is plentiful on Mars. It has been linked to active processes on Mars such as geysers of carbon dioxide gas from springtime sublimation of dry ice, and blocks of dry ice that plow lines on sand dunes by sledding down dunes on cushions of sublimated gas. One mechanism for how carbon dioxide frost might drive gully flows is by gas that is sublimating from the frost, providing lubrication for dry material to flow. Another might be slides due to accumulating weight of seasonal frost buildup on steep slopes.
Work by Dundas and others has previously pointed to winter timing of gully formation on dune and non-dune slopes, with suggested involvement of seasonal changes in frozen carbon dioxide. The new report adds evidence for the changes. The findings also make a new point that the pace of gully formation that has now been documented is swift enough that all of the fresh-appearing gullies seen on Mars can be attributed to current processes. Some earlier hypotheses attributing the gullies to action of liquid water have suggested they formed thousands to millions of years ago when climate conditions were possibly more conducive to Mars having liquid water due to variations in the planet's tilt and orbit.
Dundas' co-authors on the new report are Serina Diniega of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, and Alfred McEwen of the University of Arizona, Tucson.
"Much of the information we have about gully formation and other active processes on Mars comes from the longevity of MRO and other orbiters,” said Diniega. “This enables repeated observation of sites to examine changes over time."
Data will appear in an upcoming special issue of Icarus with multiple reports about active processes on Mars, including RSL.
"I like that Mars can still surprise us," Dundas said. "Martian gullies are fascinating features where we can investigate a process that we just don't see on Earth."
HiRISE is operated by the University of Arizona. The instrument was built by Ball Aerospace & Technologies Corp., Boulder, Colorado. The Mars Reconnaissance Orbiter Project is managed for NASA's Science Mission Directorate, Washington, by JPL.
Visit the USGS Astrogeology Center to learn more.
Visit HiRISE for more information.
Additional information about MRO is available online.These two images show changes in a gully on Mars, and illustrate that these landforms are evolving rapidly. A rubbly flow (noted by the arrows) has been deposited near the mouth of the channel between the time of the two images. Further up the slope, the channel system has been modified by both erosion and deposition. The timing of such changes is often in winter or early spring, suggesting that they are caused by the carbon dioxide frost that forms in and around most gullies every year. (High resolution image)