Category Archives: GeoPicture

Tanzania’s blood-red lake snapped from space by NASA

On March 6, 2017, NASA’s Landsat 8 satellite swooped over Tanzania and snapped some incredible pictures of its ruby-red lake.

Lake Natron.

Click for full resolution.
Image credits NASA Earth Observatory.

Northern Tanzania is home to a beautiful, bloody-crimson body of water known as Lake Natron. Apart from its striking hue, the water also has a high concentration of natural salts, making it very alkaline, up to 10.5 on the pH scale.

So what makes a lake turn ruby-red and almost as caustic as ammonia? Well, it all comes down to the area’s geology, particularly its volcanism. The lake sits about 20km north of Ol Doinyo Lengai, an active volcano that juts out of the surrounding plain. Ol Doinyo Lengai is the only volcano known to have ever released carbonatite lava (poor in silica, rich in carbonate minerals) in human history, which is more chemically similar to sedimentary rocks than other types of lava (which are predominantly silica).

Its products flow, fall, roll, and push through faults all the way to the lake, enriching it in alkaline salts and other material. Waterwise, Lake Natron is chiefly supplied by the Southern Ewaso Ng’iro River and mineral-rich hot springs that are powered by Ol Doinyo’s volcanism. Minerals and salts released by this process, particularly sodium carbonate, push the waters of Lake Natron even higher beyond water’s neutral 7 point mark on the pH scale.

Detail of the lake.
Image modified after NASA Earth Observatory.

These conditions are ripe for holoarchaea, a class of microorganisms which thrives in salty environments. As they multiply, the holoarchaea lend the water its red hue — the rainy seasons in the area runs from March to May and at the time Landsat passed over Lake Natron, the water level was particularly low and the salt ponds were very colorful.

Most animals (us too) can’t handle water as alkaline and salty as this, but Lake Natron is home to a few species which have adapted to withstand the harsh chemical conditions. Flocks of birds often camp on its shores, and tilapia fish brave its briny waters. Flamingos, in particular, favor the area as a nesting site during the dry season, since moat-like channels and the harsh waters make an ideal fortification against predators.

Lake Natron detail.

Image credits NASA Earth Observatory.

The climate here is arid. In a non-El Niño year, the lake receives less than 500 millimeters (20 inches) of rain. Evaporation usually exceeds that amount, so the lake relies on other sources—such as the Ewaso Ng’iro River at the north end—to maintain a supply of water through the dry season.

But it’s the region’s volcanism that leads to the lake’s unusual chemistry. Volcanoes, such as Ol Doinyo Lengai (about 20 kilometers to the south), produce molten mixtures of sodium carbonate and calcium carbonate salts. The mixture moves through the ground via a system of faults and wells up in more than 20 hot springs that ultimately empty into the lake. The lake, however, can be a double-edged sword — as this flamingo can attest.

GeoPicture of the Week: Petrified Wood

Petrified log at the Petrified Forest National Park. Photo by Joe Sullivan.

Just like a number of creatures, wood can fossilize too. Wood petrifies in very specific conditions in a two-stage process. The process starts when the plant material is buried under sediments and protected from decay by oxygen and organisms. Then, groundwater rich in minerals and dissolved solids flows through the sediments, gradually replacing the plant material with silica, calcite, pyrite or opal.

The result is as you can see here – a fossil body which often exhibits features of the wood, including the bark and cellular structures. Petrified wood can preserve the original structure of the stem in all its detail, down to the microscopic level. Structures such as tree rings and the various tissues are often observed features.

GeoPicture of the Week: A colorful crystal mosaic

This is a beautiful specimen, from recent finds at the Wudong Mine of China. It features several minerals: apatite, sitting in the middle sits front and center on cherry-red rhodochroite rhombs. The purple cubes are fluorite crystals, and of course, brass-yellow cubes are pyrite. Everything is surrounded by beautiful quartz crystals coming in from all over the place. It’s extremely rare that such a gorgeous rock is found, a true geological gem.

#GeoPicture of the day: Amethyst

Evitachoel / Pixabay

For all its beauty, amethyst is a fairly common variety of quartz. This here isn’t even a particularly special image, it’s how amethyst looks like most of the time. What is it about this mineral that makes it so special?

Quartz itself is the second-most-abundant mineral in Earth’s crust. Amethyst is one of the more common of the quartz varieties. Amethyst usually has a color varying from a light violet to a deep purple. The color in amethyst is usually unevenly distributed in the individual crystals. Ironically, the color is given by a technical defect – the presence of traces of built into its crystal lattice. But even when the color is deep, the content of iron in the amethyst is rather low, ranging from 10 to 100 parts per million.

Usually, amethyst crystals don’t get very large, rarely reaching 30 centimeters or more. Previously, amethyst used to be considered one of the most valuable gemstones in the world, but with many discoveries in the world (especially in Brazil), its price has dropped dramatically, up to the point where you can find it at many flea markets.

But regardless of its market value, amethyst remains one of the most cherished gemstones. Its simple beauty just makes me stop and admire it for a moment.

GeoPicture of the Week: Spaghetti Rock

Photo by Mike Beauregard.

Photo by Mike Beauregard.

What we’re seeing here is the ductility of the marble. According to the picture author, the marble dates from the Lower Proterozoic, more than 1.6 billion years ago to a period called the Aphebian Age.

When rocks are subjected to high temperatures and pressures over long periods of time, they will either transform or break. Marble is not a particularly ductile rock, but we do see it bend and take the shape imposed by the geological stress.

#GeoPicture of the WeekThe Sahara Desert in Algeria, as seen by Japan’s ALOS satellite

It’s almost poetry: this image taken by the Advanced Land Observing Satellite “DAICHI” (ALOS) satellite shows the beauty and harshness of the Sahara desert. The Japanese Space Agency (JAXA) wrote:

The heat and lack of water render vast desert areas highly unwelcoming, making satellites the best way to observe and monitor these environments on a large scale.

#GeoPicture of the Week: Odyssey hits 60,000 Mars orbits

This image shows, in false color, the region around Gale Crater on Mars. It was taken by the 2001 Mars Odyssey spacecraft – but we just call it Odyssey.

Odyssey has been orbiting the Red Planet for 14 years, 5 months and 20 days, recently celebrating a whopping 60,000 orbits around the planet, taking pictures and making valuable observations in the process. It currently holds the record for the longest-surviving continually active spacecraft in orbit around a planet other than Earth.

This mosaic is made from Thermal Emission Imaging System (THEMIS) images used to identify the different minerals on the Martian surface. Pink indicates wind-blown dust, grey is the typical mixed Martian surface and purple is basaltic rocks. The blue color observed here suggests there’s something else there as well, but we don’t know what. The Curiosity Rover might investigate that area directly.

More information about the project here.

GeoPicture of the Week: The Moon’s Geology

It’s absolutely baffling that we’ve reached a level where we can not only study the geology of the Earth, but also that of other bodies in the solar system – in this case, the Moon.

This is a false color mosaic constructed from a series of 53 images taken through three spectral filters by Galileo’s imaging system as the spacecraft flew over the northern regions of the Moon. The different colors show the compositional variations in parts of the Moon’s northern hemisphere. Bright pinkish areas are highlands materials, such as those surrounding the oval lava-filled Crisium impact basin toward the bottom of the picture. Blue to orange shades indicate volcanic lava flows. Light blue areas are thin, mineral-rich sources associated with recent impacts. The monochrome band on the right edge shows the unretouched surface of the moon. The same image, using different color filters, can be seen below:

GeoPicture of the Week: Patagonia’s shrinking ice fields

Image Credit: NASA/Landsat 8


The photo was taken with NASA’s Landat 8 satellite. Landsat is the longest-running enterprise for acquisition of satellite imagery of Earth, with the first one being launched in 1972.

Since the end of the Little Ice Age, the ice fields of Patagonia and other parts of South America have been shrinking as global temperatures have increased. A number of studies have investigated these changes and found consistent shrinking in ice mass. This is highly worrying because several communities downstream rely on the glaciers for a steady water supply.

“The focus is usually on the bigger ice fields, such as the Northern Patagonia ice field, the Southern Patagonia ice field,and on tropical glaciers,” said Mauri Pelto, a glaciologist at Nichols College. Many researchers focus on the larger ice fields because they have seen a larger mass loss.

Satellite imagery has proven invaluable in our quest to better understand Earth’s changing climate and how it will affect us all. For more information, check out NASA’s post.

GeoPicture of the Week: Beautiful Hematite

Hematite is a fairly common mineral consisting of iron and oxygen (Fe2O3). Hematite can occur in a variety of colors, from black to steel or silver-gray, brown to reddish brown, or red. The name hematite is derived from the Greek word for blood, not for its red color itself, but for the trace it leaves behind when scratched or powdered. The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor (“MGS”) and 2001 Mars Odyssey spacecraft in orbit around Mars.

GeoPicture of the Week: Snow-Covered Volcanoes Seen From Space

The picture was taken by an astronaut aboard the International Space Station (ISS), focusing on two snow-covered volcanoes in Russia’s Far East. The volcano in the center of the image is called Bolshaya Ipelka and it measures 40 kilometers (25 miles) at its base. The volcano has been inactive for a long time, but the valleys cut by glaciers along its side during the past million years are still very visible.

The much smaller Opala stratovolcano has a cone that measures 14.5 kilometers (9 miles) at the base is still active. This is still visible in its classic cone shape. In this uneroded state, Opala stretches to a much greater altitude (2475 meter or 8,120 feet) than Bolshaya Ipelka. Over the years, astronauts have taken several pictures of Kamchatka, the Russian peninsula in which the volcanoes lie. Kamchatka is very active tectonically and of much interest to geologists.

Image via NASA, taken on January 6, 2015, with a Nikon D4 digital camera using a 500 millimeter lens, provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center.

GeoPicture of the Week: The Atlantic Ocean Floor

The geology of the ocean floor is truly spectacular – perhaps even more than land geology. Unfortunately, it’s really hard to study… you know, being on the ocean floor and all.

But technician Marie Tharp and Professor Bruce Heezen from Columbia University’s Earth Institute put together several pieces of geology and geophysical information to not only create the most accurate map of the oceanic underground – but to rewrite geophysics.

Their work paved the way for general acceptance of the theories of continental drift and plate tectonic and the map itself is truly spectacular.

Here’s another map, via Houston University.

GeoPicture of the Week: Crinoid Fossils

Crinoids are marine animal (not plants) that have been around since the late Cambrian, some 500 million years ago. Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults. They are very fragile and require specific conditions to be preserved, so fossils like this one are very rare indeed.

GeoPicture of the Week: Xico Crater in Mexico

It’s a new year alright, and what better way to start it than with a GeoPicture? This is the Xico volcanic crater in Mexico.

Image via Imgur.

Located in the southern parts of of Mexico City in the municipality of Xico within the Chichinautzin volcanic field. The Chichinautzin volcanic is located in the Trans-Mexican Volcanic Belt, relatively close to the area where the Cocos tectonic plate subducts beneath the North American Plate (about 350 km / 220 miles). The filed is formed mostly from small cinder cones and shield volcanoes.

As you can see here, the crater is slowly being engulfed by urban development as more and more houses are being built around it, even at the base of its slopes. Farmers have even climbed the top of the volcano and used the fertile soil to plow fields.


Rhodochrosite Stalagmite

GeoPicture of the Week: Rhodochrosite Stalagmite ‘jawbreaker’

Rhodochrosite Stalagmite

This mineral looks so delicious, I could gobble it up like candy! It’s calleda Rhodochrosite Stalagmite, meaning it’s a Rhodochrosite formed as a stalagmite. Rhodochrosite are maybe the most famous minerals because of their red and hot pink allure. The mineral belongs to the calcite group of minerals, a group of related carbonates that are isomorphous with one another. Like all calcites, it crystallizes in the trigonal system, have perfect rhombohedral cleavage, and exhibit strong double refraction.

This particular Rhodochrosite is considered an oddity. It’s only found in Argentina, particularly in the ancient Inca Silver Mines where Rhodochrosite form as stalagmites and stalactites. According to, these “formed from precipitating water dripping from the manganese-rich rock inside the ancient mine tunnels, and kept on growing over the centuries into large stalagmites. These stalagmites are beautifully banded with concentric growth layers and are often sliced and polished into slabs for collectors”.

GeoPicture of the Week: Natural Fluorite

Look at that cleavage! Image via Imgur.

Fluorite (also called fluorspar) is a mineral consisting of calcium fluoride, CaF2. It belongs to the halide minerals, alongside common salt (called halite in its mineral form). Halide minerals crystalize in the cubic (isometric) system, which means that its crystals are basically a cubic motif. Crystal twinning is common and adds complexity to the observed crystals. Its cleavage is perfect, as can be seen in this picture.

GeoPicture of the Week: Cubic Salt Crystals at Salar de Uyuni, Bolivia

These are perfectly cubical salt crystals, spotted at Salar de Uyuni, the world’s largest salt flat, located in Bolivia.

Image via Imgur.

Each crystal belongs to a specific crystal system – for salt it’s the cubic system. This means that the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals, and this is why we see these extremely straight crystals.

Salar de Uyuni is the legacy of a prehistoric lake that went dry, leaving behind a desert-like, 11,000-sq.-km. landscape of bright-white salt, rock formations and cacti-studded islands. It is covered by a few meters of salt crust, which has an extraordinary flatness.

GeoPicture of the Week: Polished Pallasite

Image via Imgur.

This is a polished marble of a pallasite – a type of stony-iron meteorite, consisting mostly of centimeter-sized olivine crystals. Olivine is a silicate mineral often found in the Earth’s mantle.

Pallasites were once thought to originate at the core-mantle boundary of differentiated asteroids that were subsequently shattered through impacts, but that theory has been replaced recently by another one, which claims that they are impact-generated mixtures of core and mantle materials

GeoPicture of the Week: Martian Chronicles

The Astro-geology team working on analyzing the photos from Curiosity Rover is having a busy week. They recently posted this amazing picture and announced their plans for the future.

The plan for the weekend is to do a detailed analysis of the outcrop in front of us and then drive away and do some untargeted observations. Sol 1109 includes ChemCam observations of the targets “Cody” and “Leroy”, plus a Navcam dust devil search. After that, the rover will brush the dust off of Cody, with MAHLI images before and after. APXS will then analyze the target Ferdig, and then do an overnight observation of Cody.