Saturday, July 20, 2013

Devils Tower Prairie Dogs

A black-tailed prairie dog
One of the most-interesting and social rodents of North America can be found at Devils Tower National Monument: the black-tailed prairie dog. French Canadians called them prairie du chien, and later English-speaking explorers used the English translation.
   The prairie dog is actually a member of the squirrel family. They are excellent tunnelers and are aided by their small ears, short tail and powerful legs. Their tan coloring and black tail makes for excellent camouflage against the backdrop of their burrows.
   Their range has been drastically reduced over the last century due to loss of habitat and they are now mainly found on protected areas like Devils Tower National Monument or Badlands National Park in South Dakota.
   Prairie dogs live in densely populated areas called towns. Large towns are divided into wards which are separated by hills, roads, streams or patches of forest. Wards are further divided into coteries. A typical coterie contains one adult male, three or four adult females and several yearlings and juveniles. However, coteries can be as small as two or as large as 39 individuals. If there are two adult males in the same coterie, one is dominant over the other. The residents of each coterie protect their territory from intruders, including prairie dogs from other coteries in the town.
Devils Tower National Monument
   Prairie dogs use the excavated earth from their burrows to make mounds which serve as watch towers and make dikes to divert water from heavy rains. Prairie dogs repair the entrance to their burrows by pounding wet earth into place with their noses. A burrow contains several chambers including a listening post, a toilet and a multi-chambered living area. One chamber of the living area is usually built above the rest to serve as an underground lifeboat by trapping air when the burrow floods.
   Prairie dogs breed from late February until early April. 35 days after conception, four to six blind, hairless pups are born. The mother will actively protect the nest after the pups are born until they are weaned, about six weeks later.
   Prairie dogs are almost wholly vegetarian, although they will eat small insects on occasion. Tall plants are cut down both for food and to increase visibility, leaving only a thin covering of grass and other plants surrounding the burrow. The main source of water for prairie dogs comes from the moisture in the plants and roots they eat. Unlike some other prairie dogs, black-tailed prairie dogs do not truly hibernate and on warm winter days they can be seen actively foraging for vegetation.
   Many carnivores prey on prairie dogs, including coyote, fox, badgers, mink, bobcats, weasels, owls, hawks, eagles, and rattlesnakes.
   Prairie dogs communicate with each other through a variety of methods. When two individuals from the same coterie meet they exchange an identification kiss to show recognition and acceptance. A short, high-pitched warning bark is repeated several times along with a flicking of their tail when danger is sensed. When the town hears a warning bark, they will sit up to see what is causing the alarm. If the warning bark is faster and higher pitched it means a hawk or eagle has been spotted and they will run for the safety of their burrow. After the coast is clear, the prairie dog will throw its forefeet up and point its nose to the sky before coming down on all fours to signal that all is well. This call can also be used to warn prairie dogs not in the coterie that the territory is taken and to stay out.

Monday, May 20, 2013

The Northern Hawk Owl

The Northern Hawk Owl is adept at capturing rodents
under the snow due to their great hearing.

The Northern Hawk Owl is a non-migratory owl that resembles a hawk in behavior and appearance. During flight it looks similar to a Cooper's Hawk. It is one of the few owls that is primarily active during the day.
   Northern Hawk Owls are unevenly distributed throughout the boreal forest. They live mostly in open coniferous forests, or coniferous/deciduous mixed forests of Canada and Alaska, sometimes extending down to other northern states during winter or after a population explosion in their prey. They are also found across northern Eurasia, reaching Siberia at its eastern range. 
   Their prey includes small rodents (usually voles) snowshoe hares, red squirrels, and a variety of birds. During winter, they prefer to feed on ground-dwelling birds such as grouse and ptarmigans. The Northern Hawk Owl's fortune rises and falls with its prey. During prey population explosions, their numbers can swell to more than 50,000 breeding pairs, but if food is scarce, their numbers dwindle accordingly.
   The hunting strategy for the Northern Hawk Owl is to perch on a spruce tree in open forest and scan the immediate area for prey. If nothing is found, they move on to another location. When prey is spotted, the owl attacks by going from a horizontal position into a gliding dive. If the prey is further away, the bird will flap its wings a few times during the dive to make up the extra distance. This owl has superb hearing and can plunge into snow to capture rodents beneath the surface.
   The Northern Hawk Owl is one of the least studied birds in North America. They are hard to study because of a low, fluctuating population density and remote breeding locations. This lack of knowledge makes it nearly impossible to accurately estimate the population levels of this species.
   Northern Hawk Owl densities are estimated to be at most six pairs per 100 sq km. But because they live throughout the boreal forest, the North American population is thought to be quite large. In North America, over half of their breeding territory occurs in non-commercial boreal forests, so as long as nothing threatens this habitat, the species should be OK even though the populations seems to be declining. Improved monitoring should be a high priority so that we can be more confident in that assessment.

Monday, May 13, 2013

Centrifugal vs. Centripetal

I went to my daughter’s open house at school last Friday and afterwards we played a bit of tether ball before heading home. And while I’m not that great at tether ball, I can explain the forces involved in the game.

   Centrifugal force is what is often used to describe what happens to the ball as it rotates around the pole—it’s being pushed as far away from the pole as possible. But in actuality, centrifugal force is a fictitious force. The only force being applied to the ball, pulling it toward the center of rotation, is a centripetal or center-seeking force. There is nothing actually pulling the ball away from the string, what you have is just inertia as described by Newton in his First Law of Motion: An object at rest remains at rest unless acted upon by a force and an object in motion remains in motion—at a constant velocity—unless acted upon by a force. 
   Newton based his first law on the work of Galileo, who described what he called the Law of Inertia: “A body at rest remains at rest and a body in motion continues to move at constant velocity along a straight line unless acted upon by an external force.” Until Galileo, it was thought that one must exert a force in order to keep an object in motion. Galileo recognized that the reason moving bodies eventually come to rest is because of resistance forces such as friction. Without friction, bodies would continue to move at constant velocity. But I digress…
   So if you were to cut the rope as the ball is rotating what would happen? Some might think that the ball would fly away from the pole, but that’s not correct. The ball would actually move perpendicular to the pole, due to inertia. The centripetal force of the rope works against inertia by keeping the ball from travelling in a straight path. It is this constant struggle against inertia that makes it seem that the ball is trying to move away from the pole. What we call a centrifugal force is actually just the effect of inertia working against the centripetal force. Your welcome.

Monday, May 6, 2013

The Rose of Saturn

Recently, NASA release an incredible photo of Saturn’s north pole showing a massive spinning vortex of a storm they dubbed “The Rose”. This false-color image taken by the Cassini spacecraft shows the storm spanning a 2,000 km diameter which, by comparison, is 200 km wider than Hurricane Sandy. Maximum wind speeds of 530 km/h have been calculated—that is some hurricane!
   See how much you know about the ringed planet by answering these ten quiz questions, below. Good luck!

Monday, April 29, 2013


Asteroids have been making quite a few headlines as of late. Recently, we had NASA announcing its intentions to capture and asteroid robotically and bring it back for study by a manned expedition. The ten-year, $2.6 billion project would partner with private companies to capture a 500-ton, near-Earth asteroid that would be bagged, brought back, and placed in a gravitational parking lot known as the Earth-Moon lagrangian point (L2). There, a manned outpost could study it and set up a mining station to harvest its resources, especially its trapped water. Considering that it currently costs $10,000 per pound to haul water into orbit, mining it from an asteroid could save a billion dollars at current launch prices. Add to that the ability to use water to create rocket fuel by splitting it into its elemental components hydrogen and oxygen, it's no surprise that water is also called "space gold".
   On February 15, 2013, a meteor exploded over Russia’s Ural mountains in the Chelyabinsk region, injuring about a thousand people, as the shockwave blew out windows and rocked buildings. On that same day, there was a close flyby of asteroid 2012 DA14, which passed within about 27,000 km of Earth which is closer than the orbits of television and weather satellites that surround our planet. The two events were unrelated. 
Ceres, the largest asteroid
and also a dwarf planet.
   In the weeks after these events, there’s been a renewed call for creating an asteroid detection system. As it stands now, all anyone could do if we discovered a large asteroid headed toward New York City or some other large metropolitan area is “pray,” according to NASA chief Charles Bolden. We only know the whereabouts of about 10% of the estimated 10,000 city-killer asteroids. The Chelyabinsk asteroid is the largest to hit Earth since the 1908 Tunguska asteroid exploded over Siberia, leveling 80 million trees over an area of around 2,100 sq km.
   The asteroid belt lies between the orbits of Jupiter and Mars. Even though there are asteroids in other parts of the solar system, most are found here. About half the mass of the belt is contained in the four biggest asteroids: Ceres, Vesta, Pallas and Hygiea. These have average diameters of more than 400 km, while Ceres, which is also a dwarf planet, has a diameter of about 950 km. The remaining asteroids are thinly distributed and range all the way down in size to dust particles.
Vesta as imaged by the Dawn spacecraft.
   Asteroids are rocky. Because they come from the inner solar system, any ice would have been baked off by the sun long ago. Their orbits are fairly predictable, so with good observations, we can track down the big ones and determine if they’re threats.
   There are more objects beyond Neptune. The Kuiper Belt extends more than 100 times farther from the Sun than Earth. Beyond that is the Oort Cloud which extends 10,000 times farther from the Sun than Earth. These collections of small, icy bodies are remnants from the formation of the solar system. When their orbits are disturbed by other objects they can move into the inner solar system, becoming comets. As they come close to the sun that ice evaporates and creates the comet’s tail. They are less dense than asteroids, and tend to be moving faster by the time they reach the inner solar system. Some comets, like Halley’s comet which returns every 76 years, have predictable, periodic orbits.
   Knowing where an object comes from is a good indicator as to whether it is an asteroid or a comet. It’s not all black-and-white—objects from the outer solar system might be rocky and some asteroids do have some ice. But overall this is good way of thinking about them.

Sunday, April 21, 2013

The Wave

The Wave, Arizona

This incredible formation of Navajo Sandstone is stunning in its beauty. Formed during the Jurassic period about 190 million years ago, sand dunes compacted and hardened, with erosion forming the wavelike shapes in the structure over time. Everywhere you look, there are stunningly beautiful formations for hikers and photographer to enjoy. These famous undulating forms can only be reached by a rugged, pathless hike.
Characteristics of treads and risers cut 
into Navajo Sandstone at The Wave.
   The Wave is located near the Arizona/Utah border on the slopes of the Coyote Buttes. It consists of two intersecting troughs that have eroded into the sandstone. The troughs that make this formation have dimensions of about 19 x 36 meters and 2 x 16 meters. At first, infrequent runoff eroded these troughs along joints within the sandstone. After their formation, the drainage basin which fed water to these troughs shrank to the point where it no longer contributes to the erosion. Now the troughs are mostly eroded by wind which cuts characteristic erosional treads and risers into the sandstone along their steep walls. These treads and risers are oriented relative to the prevailing wind direction as it funnels through the troughs.
Cross-bedded Navajo Sandstone at The Wave.
   The Wave exposes large sets of cross-bedded sandstone which represent periodic changes in the prevailing winds during the Jurassic as huge sand dunes migrated across the desert. The thin ridges and ribs seen in The Wave are the result of the different erosion rates within the Navajo Sandstone. The sandstone is soft and fragile, so hikers needs to walk carefully to avoid damaging the small ridges.
   In places, The Wave exposes deformed layers within the Navajo Sandstone, created before the sand was turned to stone. This deformation likely represents dinosaur tracks and the fossil burrows of desert-dwelling insects.
The Wave is located near the Utah/Arizona border
between Kanab and Lake Powell.
   The Wave is located within the Paria Canyon-Vermilion Cliffs Wilderness and is administered by the Bureau of Land Management (BLM), part of the U.S. Department of the Interior. From Interstate I-15, it's about a 2-1/2 hour drive, passing through Kanab, Utah towards Lake Powell. If you want to visit The Wave, you will need to get a day-use permit. The BLM limits access to the North Coyote Buttes Wilderness to just twenty permits per day—ten in advance through an on-line lottery and ten by walk-in lottery at 9:00 am the day before one's intended hike, held at the visitor center in Kanab.

Monday, April 15, 2013

Salar de Uyuni

During the rainy season, Salar de Uyuni
becomes the world's largest mirror.

Salar de Uyuni is the world's largest salt flat at 10,600 square kilometers—about 100 times larger than the Bonneville Salt Flats in Utah. It is located in the Andes in southwest Bolivia at an elevation of 3,656 meters, making it the highest salt flats in the world. The salt flat was formed as a result of transformations between several prehistoric lakes. It is covered by a few meters of salt crust, which is extraordinarily flat. The crust serves as a source of salt and covers a pool of brine, which is exceptionally rich in lithium, of which it contains 50-70% of the world's reserves. 
Salar de Uyuni traditional salt harvest: salt is
scraped into small mounds to evaporate the water
for easier transportation.
   The salt flat is the remains of an ancient lake from about 40,000 years ago. Because it is surrounded by mountains, there is no drainage outlet and the salt collects on the lake bed as the water evaporates. The salt is scraped away from the surface by locals and piled up into mounds. This helps the water evaporate more quickly so the salt can be transported away. Salar de Uyuni contains about 10 billion tons of salt, and each year 25,000 tons are harvested by a cooperative of miners that share in the profits.
   The large area, clear skies and the exceptional flatness of the surface make Salar de Uyuni an ideal place to use to calibrate satellite altimeters. It is the major transportation route across the Bolivian Altiplano and is a major breeding ground for several species of pink flamingos. Salar de Uyuni is a climate transition zone, for towering clouds that form in the eastern part of the salt flat during the summer cannot penetrate beyond its drier western edges, near the Chilean border and the Atacama Desert.
   During the rainy season the water creates the world's largest mirror which must be seen to be believed. You can see the sky and clouds under your feet and feel like you're walking on them. Even though it is quite remote, many photographers and tourists take amazing photos at Salar de Uyuni.
   There is currently a political battle going on over the lithium resource that Salar de Uyuni hold. The Bolivian government is not willing to simply export the raw materials needed for the ubiquitous lithium-ion batteries used for electric vehicles, iPhones and other consumer electronics—they want to manufacture locally as well as protect the salt flats from damage. Bolivia is aiming to become the Saudi Arabia of lithium production and they are being courted by conglomerates such as Mitsubishi and Sumitomo who believe that the next wave of automobile batteries must come from Salar de Uyuni. Meanwhile, due to political uncertainty and poor relations with the Bolivian government, the U.S. is sitting on the sidelines.