In 2016, we published space-based imagery of Iguazú Falls—South America’s famous system of waterfalls, which is near a bend in the Iguazú River between Argentina and Brazil. Spray from the falls reaches so high that it is visible from space. A crew member aboard the International Space Station captured the photograph above on May 24, 2016.
The view from the ground is also quite compelling, attracting more than a million visitors per year. The images below show ground-based views of the falls, photographed photographed by NASA’s Alexey Chibisov from the Argentine side of the river on November 28, 2017. Chibisov took the photos while on vacation after weeks in the field with the Operation IceBridge mission.
Photo by Alexey Chibisov.
Lush, subtropical rainforest surrounds the falls. The vegetation here is part of a remaining fragment of the Atlantic Forest, which stretches from the east coast of South America inland toward the Amazon. The forest is habitat for tens of thousands of plant species and thousands of animal species.
Photo by Alexey Chibisov.
Sediment carried by the fast-moving river can impart a red-brown color to the water, especially after periods of heavy rain.
Photo by Alexey Chibisov.
The mist is the result of water that plunges as much as 260 feet (80 meters) over layers of basalt cliffs.
Every month on Earth Matters, we offer a puzzling satellite image. The November 2017 puzzler is above. Your challenge is to use the comments section to tell us what we are looking at, when the image was acquired, and why the scene is interesting.
How to answer. You can use a few words or several paragraphs. You might simply tell us the location. Or you can dig deeper and explain what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure feature in the image. If you think something is interesting or noteworthy, tell us about it.
The prize. We can’t offer prize money or a trip to Mars, but we can promise you credit and glory. Well, maybe just credit. Roughly one week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. After we post the answer, we will acknowledge the first person to correctly identify the image at the bottom of this blog post. We also may recognize readers who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have shaped the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you would like to recognize, please mention that as well.
Recent winners. If you’ve won the puzzler in the past few months or if you work in geospatial imaging, please hold your answer for at least a day to give less experienced readers a chance to play.
Releasing Comments. Savvy readers have solved some puzzlers after a few minutes. To give more people a chance to play, we may wait between 24 to 48 hours before posting comments.
Good luck!
In this satellite image, the prominent Pinacate Peaks stick out above the sand dune landscape of the Gran Desierto de Altar in Mexico’s Sonoran Province. The peaks are located just south of the Mexico-United States border. The Gran Desierto de Altar is one section of the broader Soronan Desert which covers much of northwestern Mexico and reaches into Arizona and California.
Steady, consistent winds in the area have shifted low-lying sand into dune fields in intriguing regular patterns. These same patterns of sand dune fields appear around the world in desert areas.
The volcanic peaks and cinder cones are believed to have formed from volcanic activity that first started roughly 4 million years ago — most likely due to the plate tectonics that also formed the Gulf of California around the same time. The most recent activity was perhaps 11,000 years ago. During the late 1960s, NASA trained astronauts in field geology at a number of sites around the world, including Pinacate Peaks, as preparation for the lunar landings.
The natural color image here is from the Landsat 8 satellite using its Operational Line Imager (OLI) instrument. The image was acquired on October 3, 2017. The volcanic cinder cone field stains the landscape of bright sand and tall dunes in the El Pinacate y Gran Desierto de Altar Biosphere Reserve.
NOTE: In a previous version of this post, I featured the EO-1 ALI image below, and an astute reader pointed out that these peaks, while in the Biosphere Reserve, are not Pinacate Peaks, but rather the Sierra de Rosario range nearby. I am geographically and tectonically embarassed…
The natural color image here is from the now-defunct Earth Observing 1 (EO-1) satellite using its Advanced Land Imager (ALI). The image was acquired on December 16, 2012. This late-year scene was just days before the solstice (the farthest south the Sun appears in the sky), so the tallest sand dunes and the volcanic peaks cast unusually long shadows across the ground.
EO-1 was launched in November 2000 as an engineering testbed for new sensor technology; in particular, the ALI instrument was a predecessor for the Landsat 8 Operational Land Imager. The EO-1 mission was so successful that it was extended past its original 18-month mission, and was only recently retired after 17 years of operation.
This post is republished from the Landsat science team page.
In the giddy, early days following the flawless launch of Landsat 8, as the satellite commissioning was taking place, the calibration team noticed something strange. Light and dark stripes were showing up in images acquired by the satellite’s Thermal Infrared Sensor (TIRS).
Comparing coincident data collected by Landsat 8 and Landsat 7 — acquired as Landsat 8 flew under Landsat 7, on its way to its final orbit — showed that thermal data collected by Landsat 8 was off by several degrees.
This was a big deal. The TIRS sensor had been added to the Landsat 8 payload specifically because it had been deemed essential to a number of applications, especially water management in the U.S’s arid western states.
The TIRS error source was a mystery. The prelaunch TIRS testing in the lab had shown highly accurate data (to within 1 degree K); and on-orbit internal calibration measurements (measurements taken of an onboard light source with a known temperature) were just as good as they had been in the lab. But when TIRS radiance measurements were compared to ground-based measurements, errors were undeniably present. Everywhere TIRS was reporting temperatures that were warmer than they should have been, with the error at its worst in regions with extreme temperatures like Antarctica.
After a year-long investigation, the TIRS team found the problem. Stray light from outside the TIRS field-of-view was contaminating the image. The stray light was adding signal to the TIRS images that should not have been there—a “ghost signal” had been found.
Scans of the Moon, together with ray tracing models created with a spare telescope by the TIRS instrument team, identified the stray light culprit. A metal alloy retaining ring mounted just above the third lens of the four-lens refractive TIRS telescope was bouncing out-of-field reflections onto the TIRS focal plane. The ghost-maker had been found.
With the source of the TIRS ghosts discovered, Matthew Montanaro and Aaron Gerace, two thermal imaging experts from the Rochester Institute of Technology, were tasked with getting rid of them.
Montanaro and Gerace had to first figure out how much energy or “noise” the ghost signals were adding to the TIRS measurements. To do this, a stray light optical model was created using reverse ray traces for each TIRS detector. This essentially gave Montanaro and Gerace a “map” of ghost signals. Because TIRS has 1,920 detectors, each in a slightly different position, it wasn’t just one ghost signal they had to deal with— it was a gaggle of ghost signals.
To calculate the ghost signal contamination for each detector, they compared TIRS radiance data to a known “correct” top-of-atmosphere radiance value (specifically, MODIS radiance measurements made during the Landsat 8 / Terra underflight period in March 2013).
Comparing the MODIS and TIRS measurements showed how much energy the ghost signal was adding to the TIRS radiance measurements. These actual ghost signal values were then compared to the model-based ghost signal values that Montanaro and Gerace had calculated using their stray light maps and out-of-field radiance values from TIRS interval data (data collected just above and below a given scene along the Landsat 8 orbital track).
Using the relationships established by these comparisons, Montanaro and Gerace came up with generic equations that could be used to calculate the ghost signal for each TIRS detector.
Once the ghost signal value is calculated for each pixel, that value can be subtracted from the measured radiance to get a stray-light corrected radiance, i.e. an accurate radiance. This algorithm has become known as the “TIRS-on-TIRS” correction. After performing this correction, the absolute error can be reduced from roughly 9 K to 1 K and the image banding, that visible vestige of the ghost signal, largely disappears.
“The stray light issue is very complex and it took years of investigation to determine a suitable solution,” Montanaro said.
This work paid off. Their correction—hailed as “innovative” by the Landsat 8 Project Scientist, Jim Irons—has withstood the scrutiny of the Landsat Science Team. And Montanaro and Gerace’s “exorcism” has now placed the Landsat 8 thermal bands in-line with the accuracy of the previous (ghost-free) Landsat thermal instruments.
USGS EROS has now implemented the software fix developed by these “Landsat Ghostbusters” as part of the Landsat Collection 1 data product. Savvy programmers at USGS, led by Tim Beckmann, made it possible to turn the complex de-ghosting calculations into a computationally reasonable fix that can be done for the 700+ scenes collected by Landsat 8 each day.
“EROS was able to streamline the process so that although there are many calculations, the overall additional processing time is negligible for each Landsat scene,” Montanaro explained.
Gerace is now determining if an atmospheric correction based on measurements made by the two TIRS bands, a technique known as a split window atmospheric correction, can be developed with the corrected TIRS data.
Meanwhile, Montanaro has been asked to support the instrument team building the Thermal Infrared Sensor 2 that will fly on Landsat 9. A hardware fix for TIRS-2 is planned. Baffles will be placed within the telescope to block the stray light that haunted the Landsat 8 TIRS.
The Landsat future is looking ghost-free.
Related Reading:
+ RIT University News
+ TIRS Stray Light Correction Implemented in Collection 1 Processing, USGS Landsat Headline
+ Landsat Level-1 Collection 1 Processing, USGS Landsat Update Vol. 11 Issue 1 2017
+ Landsat Data Users Handbook, Appendix A – Known Issues
References:
Montanaro, M., Gerace, A., Lunsford, A., & Reuter, D. (2014). Stray light artifacts in imagery from the Landsat 8 Thermal Infrared Sensor. Remote Sensing, 6(11), 10435-10456. doi:10.3390/rs61110435
Montanaro, M., Gerace, A., & Rohrbach, S. (2015). Toward an operational stray light correction for the Landsat 8 Thermal Infrared Sensor. Applied Optics, 54(13), 3963-3978. doi: 10.1364/AO.54.003963 (https://www.osapublishing.org/ao/abstract.cfm?uri=ao-54-13-3963)
Barsi JA, Schott JR, Hook SJ, Raqueno NG, Markham BL, Radocinski RG. (2014) Landsat-8 Thermal Infrared Sensor (TIRS) Vicarious Radiometric Calibration. Remote Sensing, 6(11), 11607-11626.
Montanaro, M., Levy, R., & Markham, B. (2014). On-orbit radiometric performance of the Landsat 8 Thermal Infrared Sensor. Remote Sensing, 6(12), 11753-11769. doi: 10.3390/rs61211753
Gerace, A., & Montanaro, M. (2017). Derivation and validation of the stray light correction algorithm for the Thermal Infrared Sensor onboard Landsat 8. Remote Sensing of Environment, 191, 246-257. doi: 10.1016/j.rse.2017.01.029
Gerace, A. D., Montanaro, M., Connal, R. (2017). Leveraging intercalibration techniques to support stray-light removal from Landsat 8 Thermal Infrared Sensor data. Journal of Applied Remote Sensing, Accepted for Publication.
Every month on Earth Matters, we offer a puzzling satellite image. The October 2017 puzzler is above. Your challenge is to use the comments section to tell us what we are looking at, when the image was acquired, and why the scene is interesting.
How to answer. Your answer can be a few words or several paragraphs. (Try to keep it shorter than 200 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure speck in the far corner of an image. If you think something is interesting or noteworthy, tell us about it.
The prize. We can’t offer prize money or a trip to Mars, but we can promise you credit and glory. Well, maybe just credit. Roughly one week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. After we post the answer, we will acknowledge the person who was first to correctly ID the image at the bottom of this blog post. We may also recognize certain readers who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have played a role in molding the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you want us to recognize, please mention that as well.
Recent winners. If you’ve won the puzzler in the last few months or work in geospatial imaging, please sit on your hands for at least a day to give others a chance to play.
Releasing Comments. Savvy readers have solved some of our puzzlers after only a few minutes or hours. To give more people a chance to play, we may wait between 24-48 hours before posting the answers we receive in the comment thread.
Good luck!
Atmospheric rivers stretched from Asia to North America in October 2017. Learn more.
If you live on the West Coast of North America, you have probably heard meteorologists talk about “atmospheric rivers” — the narrow, low-level plumes of moisture that often accompany extratropical storms and transport large volumes of water vapor across long distances. When atmospheric rivers encounter land, they can drop tremendous amounts of rain and snow. That can be good for replenishing reservoirs and for quenching droughts, but these remarkable meteorological features can also trigger destructive floods, landslides, and wind storms.
During the past decade, atmospheric rivers have fueled a flood of another type: scientific research papers. Prior to 2004, fewer than 10 studies mentioned atmospheric rivers in any given year; in 2015, about 200 studies were published on the matter. The availability of increasingly sophisticated satellite and aircraft data has fueled the trend, according to a recent article in the Bulletin of the American Meteorological Society. Here’s a sampling of what scientists have learned about these rivers in the sky.
They Can Bring Rains, Winds, And Lots of Damage
In a study led by Duane Waliser of NASA’s Jet Propulsion Laboratory and published in Nature Geoscience, researchers showed that atmospheric rivers are among the most damaging storm types in the middle latitudes. Of the wettest and windiest storms (those ranked in the top 2 percent), atmospheric rivers were associated with nearly half of them. Waliser and colleagues found that atmospheric rivers were associated with a doubling of wind speed compared to all storm conditions.
They Shift With The Seasons
During the winter, atmospheric rivers in the Pacific generally shift northward and westward, Bryan Mundhenk of Colorado State University and colleagues concluded in a study. They also found that the El Niño/Southern Oscillation (ENSO) cycle can affect the frequency of atmospheric river events and shift where they occur. The research was based on data processed by MERRA, a NASA reanalysis of meteorological data from satellites.
They Aren’t Just a West Coast Thing
Atmospheric rivers are a global phenomenon and responsible for about 22 percent of all water runoff. One recent study from a University of Georgia team underscored that the U.S. Southeast sees a steady stream of atmospheric rivers. “They are more common than we thought in the Southeast, and it is important to properly understand their contributions to rainfall given our dependence on agriculture and the hazards excessive rainfall can pose,” said Marshall Shepherd of the University of Georgia. Other studies note that atmospheric rivers have contributed to anomalous snow accumulation in East Antarctica and extreme rainfall in the Bay of Bengal.
Climate Change Could Alter Them
A recent study led by Christine Shields of the National Center for Atmospheric Research suggests that climate change could push atmospheric rivers in the Pacific toward the equator and bring more intense rains to southern California. The modeling calls for smaller increases in rain rates in the Pacific Northwest. Another ensemble of models shows a in the number of days with landfalling atmospheric rivers in western North America.
Satellites Are Key to Studying Their Precipitation
While there are few ground-based weather stations in the open ocean to tally how much rain falls, satellites such as those included in the Global Precipitation Measurement (GPM) mission can estimate precipitation rates from above. “Satellites have proven valuable over both the ocean and land, though uncertainties are often larger over land because of complicating factors like the terrain and the presence of snow on the surface,” said Ali Behrangi, the author of a study that assessed the skill of different satellite-derived measurements of precipitation rates.
NASA Earth Observatory images by Jesse Allen, using VIIRS data from the Suomi National Polar-orbiting Partnership.
You have probably heard or read that it has been rather smoky out West this year. Dozens of large wildfires have raged through forests in British Columbia, Alberta, Washington, Oregon, Idaho, California, and other states this fire season. Intense blazes are lofting up so much smoke that huge plumes have been blowing across the country—and even turning up in Europe. We checked with a few scientists who specialize in studying wildfires for an update on what is going on.
EO: How does this fire season compare to past years?
The western fire season has been quite active this year. British Columbia has surpassed its greatest burned area in the modern era. While its unlikely that this season will be record-breaking in the western U.S., it is above normal relative to the past decade, which has seen abundant fire activity.
— John Abatzoglou, University of Idaho
EO: Is climate change exacerbating these fires?
Because we have let fuels build up in the western U.S., it is difficult to tell in many ecosystems what is weather-driven vs. climate-driven until we get back to normal fuel loads. This 2013 PNAS paper tries to answer the climate question given the artificially increased fuel loadings. They found that climate change is responsible for 55 percent of the observed increasing fuel aridity. — Jessica McCarty, Miami University
EO: Are bark beetles making these fires worse?
No, the bark beetle outbreaks have little-to-no relationship with trends in area burned or the ecological severity of fires. I think this continues to be a big misconception with the public, which is understandable because climate is a key driver of both bark beetle outbreaks and wildfires. Many people jump to the conclusion that bark beetle outbreaks are causing fires. But it is likely a classic case of correlation without causation. — Brian Harvey, University of Washington
EO: If there was one thing you wished Americans understood about wildfires in the West, what would it be?
Be careful with fire. Smokey the Bear is trying to educate you on the risk—listen. Heed fire risk and fire weather warnings. Don’t build campfires unless you have to. Don’t go off-roading during droughts and heat waves. Be careful with your cigarette butts. — Jessica McCarty, Miami University
Even though no one is a fan of widespread smoke, wildfires aren’t inherently “bad” [when they are in unpopulated areas]. One continuing challenge is figuring out how to live with fire as part of the system as more people settle in the region during an era of changing environmental conditions. — John Abatzoglou, University of Idaho
NASA Earth Observatory images by Jesse Allen and Jeff Schmaltz, using Suomi NPP OMPS data provided courtesy of Colin Seftor (SSAI).
NASA Earth Observatory images of Barbuda by Joshua Stevens, using Landsat data from the U.S. Geological Survey.
We recently posted several striking pairs of satellite images of Caribbean islands before and after they were hit by Hurricane Irma. The images show lush, green vegetation turning a dark shade of brown. We were curious about what exactly caused the damage and how quickly vegetation might recover, so we checked in with Edmund Tanner, a University of Cambridge ecologist who has authored multiple studies about vegetation damage and recovery after Caribbean hurricanes.
EO: What were the primary mechanisms that turned the islands brown? Leaves blown away by the wind? Mud and debris covering them up? Salt spray killing them off?
Away from the sea (100 meters or so), most of the green to brown is the loss of green leaves because they were blown off. Native vegetation on these islands has been through hundreds of hurricanes since the last major change of climate (10,000 years ago, the end of the most recent ice age) and have been naturally selected to lose leaves and small branches and re-sprout. I doubt if it is mud since the fairly heavy rain will have washed that off. Most of the water falling on the vegetation would have be fresh—rain—not sea spray.
EO: How long will it take for the vegetation to recover?
My guess is the greening up in the lowlands will take 6 months, with a lot happening in the first 3-4 months. You can probably measure that from satellite images. On the ground, there will be lots of sprouts on tree trunks. For larger trees, the surviving branches will produce leaves and small branches and slowly these will shade out and kill the epicormic shoots produced on the lower parts of trunks
.
EO: What about storm surge? Was that a major factor in killing trees and other vegetation?
Salt water from storm surge may have killed trees whose roots were inundated with it. Those trees will take much longer to recover because the soil will need to be desalinated naturally by rain, and seeds will have to germinate and grow. The areas involved are not likely to be large—a fringing zone of a few hundred hectares in some places.
EO: How useful are satellites in assessing vegetation damage caused by hurricanes?
Very useful. Especially for measuring the change in green from before the hurricane to brown immediately after the hurricane, to greening up over weeks and months after the hurricane. Modern analyses of satellite images could also show the decrease in individual tree canopy size if trees lost big branches and only regrew them slowly.
NASA Earth Observatory images of the virgin islands by Joshua Stevens, using Landsat data from the U.S. Geological Survey.
Every month on Earth Matters, we offer a puzzling satellite image. The August 2017 puzzler is above. Your challenge is to use the comments section to tell us what we are looking at, when the image was acquired, and why the scene is interesting.
How to answer. Your answer can be a few words or several paragraphs. (Try to keep it shorter than 200 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure speck in the far corner of an image. If you think something is interesting or noteworthy, tell us about it.
The prize. We can’t offer prize money or a trip to Mars, but we can promise you credit and glory. Well, maybe just credit. Roughly one week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. After we post the answer, we will acknowledge the person who was first to correctly ID the image at the bottom of this blog post. We may also recognize certain readers who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have played a role in molding the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you want us to recognize, please mention that as well.
Recent winners. If you’ve won the puzzler in the last few months or work in geospatial imaging, please sit on your hands for at least a day to give others a chance to play.
Releasing Comments. Savvy readers have solved some of our puzzlers after only a few minutes or hours. To give more people a chance to play, we may wait between 24-48 hours before posting the answers we receive in the comment thread.
Good luck!
Answer: The image above shows the burn scar left by a palm swamp fire in Brazil along the Peruaçu River. Rather than producing big, orange flames and billowing plumes of smoke, this fire smoldered underground in dried out, carbon-rich soil and likely peat. The fire spread slowly through soil and roots, but it was able to move up the hollow trunks of palm trees in the area and burn off the canopy. Nobody guessed the location, but congratulations to Monica Craig and Lee Hurst for guessing that it was related to a fire. Read more about the image in our September 5, 2017, Image of the Day.
NASA Earth Observatory image by Jesse Allen, using Landsat data from the U.S. Geological Survey. The image was captured on August 3, 2017, by the Operational Land Imager (OLI) on Landsat 8.
Scientists around the world have been using satellites to monitor a wildfire in Greenland. In a place better known for ice, just how unusual is this fire? NASA Earth Observatory checked with Earth science experts Ruth Mottram, Jessica McCarty, and Stef Lhermitte to find out. Mottram is a climate scientist at the Danish Meteorological Institute; Lhermitte is remote sensing scientist at Delft University of Technology; and McCarty is a geographer at Miami University.
How unusual is this fire?
Mottram: Many of my colleagues at the Danish Meteorological Institute (DMI) were a bit surprised at first, but it was clear talking to both the Greenland weather forecasters (they do three month rotations to the airport at Kangerlussuaq) and to some of the older guys that fires do happen reasonably regularly, particularly in the west and south. However, they are not always reported either officially or in the news unless the fire is close to a settlement or affecting shipping or flights. This fire seems to be a fairly large one, but there has been no systematic attempt to gather evidence or data on Greenland’s fires – at least not at DMI. I have never heard of anyone else in Denmark doing it either, so it is a bit hard to be more precise than that.
McCarty: This is a hard question to answer, and I keep telling media reporters the same thing: we need to have the wildfire history analyzed before we know how unusual this is. I can tell you from the global wildfire science community that I am a part of, we would have never thought the we would need to make a wildfire history to understand the fire regime in Greenland. So that part is unusual.
Lhermitte: I completely agree with Jessica. I used to be a wildfire remote sensing scientist (finished my PhD on African wildfires in 2008), but I have shifted since then to the cryosphere community (including some work on Greenland’s ice). It was a big surprise to me to see both worlds combined on Monday when I first noticed a Greenland fire tweet. Now it is clear that fires have occurred before, but that we basically lack a good record. MODIS gives us a glimpse, but the sensor cannot detect fires through clouds, and the record is short. Based on what I have seen, the 2017 fire is the biggest one on the MODIS record, but the record is sparse and incomplete.
I know you have done some looking through MODIS and Landsat satellite data for evidence of past fires in Greenland. What have you found?
Lhermitte: I looked back at the record of MODIS active fire detections since 2002 and made a quick overview map. In the map below, fire detections are marked with circles. Higher confidence fires are red; lower confidence fires are yellow. In most years, the satellite flags about 5 pixels as having active fires. In 2015, it flagged about 20 pixels. There were over 40 pixels flagged in 2017, so this year has been exceptional. Note: Most of these detections are probably campfires or false detections—not uncontrolled wildfires. There have been two big wildfires: the one happening now and one in August of 2015.
McCarty: Overall, 2017 appears to be a larger fire season than any year since 2001. But from a remote sensing point of view, this is a difficult place to study the fire regime using satellite-based active fire detections (because of cloudiness and other factors). The Landsat/Sentinel-2/Deimos, etc. burn scar images will be more helpful.
Mottram: I have not looked into any of the specific data, but I have heard anecdotes about fires in Narsarsuaq close to the DMI ice service reconnaissance station in the south of Greenland, in the Kobbefjord close to Nuuk, and just to the north of Sisimiut near this one. There was also a large fire in 2008 near Eqi, close to Ilulissat, which the Greenland press reported was caused by a tourist burning rubbish but failing to put the fire out.
One of you said on social media that you think the fire may be burning through peat. Are you sure? How can you tell?
McCarty: The fire line has not moved much in comparison to a wildfire in a grassland or forest. However, Stef made an awesome Sentinel-2 animation that shows the fire line moving some. I still think it is peat with a mix of grasses and moss (given the Google Earth Pro and Deimos imagery), but how deep the peat is difficult to ascertain. A recent study in the Qaanaaq region (north of where these wildfires are) found five times more peat in the soil distribution and soil content than previously reported. Also, historically, peat houses were constructed in this area of Greenland, which means there are peat deposits nearby. Short grasses with underlying peat is my working hypothesis for now since we are onto day 11 of the fire.
Mottram: I am not really a soils expert, and Greenland really suffers from having little detailed mapping of this kind. Also, Greenland is pretty diverse from north to south and east to west. There are high rocky mountains and permafrost. The south has sheep pasture and even some areas of forest; the north has large areas with low vegetation cover. However, there are also extensive areas of peat cite in the scientific literature.
Do you think this fire was triggered by human activity or lightning? Do we know what triggers most fires in Greenland?
McCarty: I still can’t find any indication that this was lightning, so it must be human activity. Greenlandic/Danish news reports are reporting that hikers and tourists should stay from this area, so I would assume that humans are on the landscape there.
Mottram: I can’t really say for sure. Lightning is not impossible, but neither is human activity. It is the middle of the hunting/fishing/berry-picking/hiking season, and this area is known for reindeer. In fact, the Greenland press had an interview with a reindeer hunter who had to turn back from visiting because of the smoke in the fjord. Actually, the hunter wanted the fire put out by the authorities, so he could go hunting there.
What has the weather been like in Greenland during the last few months? Has it been unusually hot or dry where this fire is burning?
Mottram: It has been a very dry summer in the south but also quite dry in this region, and the fire was preceded by some relatively high temperatures. My climatologist colleague John Cappelen tells me that the DMI station at Sisimiut measured an precipitation anomaly of -30.0 millimeters for June and -20.7 millimeters for July compared to the mean precipitation of 1981-2010. In other words, there was almost no rain in June and a bit more than half the usual rainfall in July. There have also been some warm days in Sisimiut (or at least at the airport where the weather station is), particularly towards the end of the month. The monthly average temperature was 7.1 Celsius compared to a 1961-1990 average of 6.3 Celsius in July. The trend has continued into August as well.
This fire got me wondering why there are ice-free areas along Greenland’s coast where vegetation grows. Are these relatively new features? How do you think they got there?
Lhermitte: These ice free coastal areas are mainly the result of the bedrock topography, where the coastal Greenland areas are much more elevated than the interior of Greenland. Since the last glacial maximum, the ice sheet has partly retreated and exposed more land. If the ice sheet would retreat further, we would see more of the inner, lower land exposed.
Mottram: The ice sheet is more or less in equilibrium with the climate, so it is where it is because that is where the glaciers can flow. During the last glacial maximum, the ice sheet extended far out onto the continental shelf and connected (in the north west) with the Laurentide ice sheet in North America. Then, with warming after the last glacial period, the ice sheet retreated. (That is, more ice was melting and calving away than was being replenished by snowfall.) The ice sheet has been more or less stable in its present extent for about the last 10,000 years (with some smaller advances and retreats responding to more local climate variability).
