Today I have some appointments, including looking at a rock collection in Gwinn. Then I'll head home to finish all my custom mineral art orders.
I have not had a chance to get out and take any pictures, so for today's blog posting I'll see what new photos the International Space Station astronauts have of our cosmic home.
First are photos of Sahara sand dunes.
In the area to the bottom right of the inner circle above, the smaller sand dunes in the valley have been migrating over the last decade, as observed from space.
This sequence features a series of horn-shaped “barchan” dunes clustered in a narrow corridor between lines of dark-toned hills. The horns point in the direction of dune migration under the influence of the prevailing winds. Thick zones of rippled, light-toned dunes are visible at the bottom of the images, with dry river channels in the center and upper parts.
The larger dunes maintain their shape and size well enough to be identified in these images taken nine years apart. The 2003 image was obtained from Google Earth, while the 2013 photo was taken by an astronaut onboard the ISS. Comparison of the 2003 and 2013 images shows that five larger dunes appear to have moved. Measurements show that the dunes have moved hundreds of meters (#1 moved 316 meters, #2 moved 275 m, #3 moved 405 m, #4 moved 318 m, and #5 moved 381 m). Arrows show the direction and distance of movement.
Dunes 3 and 5 have moved furthest, following the well-known phenomenon that smaller dunes move faster. The smallest dunes move so fast that they cannot be tracked over a decade—because they are absorbed by larger dunes; because they move into hilly terrain and break up; or because newer, small dunes are shed from the horns of the larger dunes.
The opportunities for comparisons of the landscape are growing with each new year that we send humans and satellites into space. The imagery is quite valuable to remote-sensing scientists. For example, where large masses of sand move across highways or into farm fields, as is common on the edges of deserts, they cause great environmental damage and cost. With comparative imagery, it is now possible to predict when dunes are likely to cause such damage so that mitigation efforts can be put in place.
The above image shows the Sakura-jima volcano emitting a dense plume of ash over the Japanese island of Kyushu on November 23, 2013. Currently Japan’s most active volcano, Sakura-jima explodes several hundred times each year. These eruptions are usually small, but the larger eruptions can generate ash plumes that rise 3,800 meters (12,000 feet) or more above the 1,040-meter (3,410-foot) summit.
While flying over Antarctica aboard a P-3 aircraft in November 2013, Operation IceBridge project scientists took the above photograph of Taylor Valley, one of Antarctica’s unique dry valleys. This valley is one of the most remote and geologically exotic places in the world. At the lower right of the photograph, “Blood Falls” appears as a small, dark smudge. The name refers to the stain of red that coats part of the glacier and seeps down toward Lake Bonney in a pattern that makes it look like a blood-red waterfall. The red comes from microbes living within a pool of ancient seawater that has been trapped beneath Taylor Glacier for at least 1.5 million years. Due to the activity of the microbes, the seawater is enriched with ferrous hydroxide (an iron-containing salt), which quickly oxidizes and turns red as it seeps out of a crack in the glacier.
The above image shows the same area from space that was captured by the Operational Land Imager satellite. While ice and snow covers most of Antarctica, Taylor Valley and the other dry valleys are conspicuously bare. Inland mountains—the Transantarctic Range—force moisture out of the air as it passes over, leaving the valley in a precipitation shadow. The lack of precipitation leaves dramatic sequences of exposed rock. In both the satellite image and photograph, the tan bands are sandstone layers from the Beacon Supergroup, a series of sedimentary rock layers formed at the bottom of a shallow sea between 250 million and 400 million years ago. Throughout that period, Earth’s southern continents were locked into the supercontinent Gondwana.
The dark band of rock that divides the sandstone is dolerite (sometimes called diabase), a volcanic rock that forms underground. The distinctive dolerite intrusion—or sill—is a remnant of a massive volcanic plumbing system that produced major eruptions about 180 million years ago. The eruptions likely helped tear Gondwana apart.
The dominant feature in the photograph—Taylor Glacier—is notable as well. Like other glaciers in the Dry Valleys, it is “cold-based,” meaning its bottom is frozen to the ground below. The rest of the world’s glaciers are “wet-based,” meaning they scrape over the bedrock, picking up and leaving obvious piles of debris (moraines) along their edges.
Cold-based glaciers flow more like putty, pushed forward by their own weight. Cold-based glaciers pick up minimal debris, cause little erosion, and leave only small moraines. They even look different from above. Instead of having surfaces full of crevasses, cold-based glaciers are comparatively flat and smooth.
Between November 29 and December 2, 2013, a rare meteorological event filled the Grand Canyon with an ocean of clouds. This rare ground-hugging fog may only happen once a decade, or even less often. The photo above from Mather Point is one of more than two dozen that Grand Canyon National Park posted to its Flikr photostream.
The fog was trapped in the canyon by a temperature inversion, which happens when the air near the ground is cooler than the air above it. A high-pressure system brought low temperatures, clear skies, and calm winds to the Grand Canyon. During the long nights, the ground cooled quickly, chilling the air immediately above it. The air higher in the atmosphere did not cool as quickly, and so an inversion developed. Without wind to stir it, cold dense air was trapped beneath a more buoyant layer of warm air.
The inversion was only half of the story. A few days earlier, a winter storm dumped a foot of snow at the Grand Canyon Rim. The precipitation left the ground and the air above it very moist. As the air near the ground cooled at night, the water condensed into fog, which was trapped in the canyon by the temperature inversion.
The 2013 fog event was unusual because of its extent, as shown in the above image, captured by the NASA’s Terra satellite. In the satellite image, taken mid-morning on November 30, the fog seeps into the eastern section of the Grand Canyon, conforming to the shape of the canyon walls. Fog and low clouds hang over the entire landscape east of the canyon.