Wednesday, February 28, 2007

The Warm Sector

Another major Pacific storm is bearing down on the Midwest and, this time, Missouri is in the danger zone. As of late this afternoon, the cold front stretched from eastern New Mexico to southern Iowa, bisecting the State of Kansas. It was 25 in Denver, 34 in Omaha and 33 in Des Moines; at the same time, it was 80 in Oklahoma City, 70 in Little Rock and in the sixties throughout Missouri.

The warm sector ahead of the storm is the zone at risk for severe thunderstorms. As the storm front arrives, cold air undercuts and lifts the warm, moist air. In addition, strong, southerly winds collide with high energy westerlies, producing rotation in the rising, unstable air mass; high winds, large hail and tornados often result. The center of the storm is currently in southeast Colorado but will race to northeast Kansas by tonight, dragging the cold front with it.

Such high intensity storms are common along the Gulf Coast in late winter but more typically invade Missouri from April through June. Come midnight, it will surely sound like spring.

Monday, February 26, 2007

An Invasion of Harriers

Northern harriers, formerly known as marsh hawks, fly low over grasslands, wetlands and crop fields, tilting, flapping and gliding as they search for mice, voles and frogs. Equipped with long wings and a long tail, they are easily identified by their prominant white rump. Adult males are light gray above, with a black fringe at the end of each wing; their underwings, chest and abdomen are white. Females and immatures are brown above, with brown streaking of the chest and sides; immatures also have a light brown abdomen.

Yesterday, on my trip back to Missouri, I took a southern route across Kansas, driving from Garden City to Dodge City to Wichita. Passing through a rolling landscape of grasslands and crop fields, I was amazed by the number of harriers that I saw; there seemed to be one every mile or so and it's a long way across Kansas! What's more, all but a handful were adult males.

Northern harriers are migratory hawks. While they can be seen across central latitudes of North America throughout the year, they are primarily summer residents in the northern states and winter visitors in the Gulf Coastal region. During these seasonal migrations, the adult males are the last to depart in the fall and the first to arrive in the spring. What I saw yesterday was likely the vanguard of their spring exodus, perhaps enhanced by a winter of heavy snows and ice across the Plains.

Sunday, February 25, 2007

Snows and the Storm

My plan to drive back to Missouri from our Colorado farm was complicated by a monster storm on the Plains. By noon yesterday, the storm was centered in southern Kansas and was sending severe thunderstorms and tornados across the lower Mississippi Valley. Heavy snow was falling to the north and, on its west fringe, a blizzard raked the High Plains. Interstate 70 was shut down from the east side of Denver to the Kansas border and I decided to skirt the storm by heading south. Taking U.S. 50 east from Pueblo, I made it as far as La Junta before a ground blizzard closed that highway.

After a night in southeast Colorado, I started out before dawn on a mostly clear road. Only a soft north breeze persisted and the sun rose in a clear sky as I entered Kansas. Just west of Syracuse, I encountered a huge flock of snow geese resting and feeding in a snowy crop field. The flock was noticeably restless, with groups of a hundred or more rising into the cold morning air and then resettling as other groups took flight. No doubt, the entire flock would be heading north by later in the day.

I suspect that these snow geese had wintered in New Mexico and took advantage of the strong, southerly winds ahead of the storm to begin their migration to the Arctic. As the storm moved east, the winds shifted from the north and, facing a head-on blizzard, the flock took refuge in the field. Humans are not the only creatures to face travel nightmares!

Saturday, February 24, 2007

The Flamboyant Magpie

For the birder who makes his initial visit to the American West, the black-billed magpie will likely be the first new addition to his life list. Noisy and conspicuous, this large bird is easily identified by his black and white plumage and long tail; the black feathers of his wings and tail show a greenish tinge in bright sunshine. Black-billed magpies are common from the western High Plains through the intermountain region to the Pacific Northwest and southern Alaska; their yellow-billed cousins inhabit central and southern California. Both species favor open woodlands.

Members of the crow and jay family, magpies are omniverous, feeding on waste grain, seeds, berries, insects, eggs, nestlings, carrion and small mammals; they are often spotted on the backs of elk and cattle, feasting on ticks. By late February, magpies are beginning to construct or repair their huge nest of sticks and will breed before the snow season is over. Once abandoned, these nests are often used by great horned owls.

Friday, February 23, 2007

Back to the Cretaceous

After being covered with ice and snow for more than two months, the recent warm weather has turned the plains of western Kansas into vast, meltwater lakes. Country roads are flooded, the winter wheat crop is threatened and cattle are marooned near the barns. For a region that is semiarid and must irrigate its fields with water from the dwindling Ogallala Aquifer, the current flooding might be considered a godsend; unfortunately, the deeper soil remains frozen and any long term benefit seems unlikely.

Looking out on this flooded landscape, one might wonder if the Cretaceous Sea is making a comeback. During that Period, some 80 million years ago, a broad, shallow seaway stretched from the Gulf of Mexico to the Arctic Ocean, covering much of what is now the High Plains. Pierre shale, deposited in that Cretaceous sea, underlies the region and remnant towers of marine limestone still dot Kansas, eastern Colorado and western Nebraska. As one might expect, fossils of ancient sea turtles, squid, sharks, marine reptiles and aquatic dinosaurs have been found in these deposits.

The current flooding will likely get worse before it gets better. There is still plenty of snow cover and, adding insult to injury, a major Pacific storm is forecast for this weekend. Heavy rains and thunderstorms will preceed the front while high winds and "backside snow" will follow.
It's just too much of a good thing at the wrong time!

Thursday, February 22, 2007

Snipe Crossing

While they inhabit much of the U.S. and Canada, common snipes are not often seen by the casual naturalist. They prefer wooded streams and marshlands where they tend to be reclusive and usually feed alone. When spotted, they have often been flushed accidentally. Until yesterday, I had surely never seen one from the highway.

Heading out to our Colorado farm, I was in eastern Kansas when a bird entered my field of vision. Noting its rapid flight on bent wings, I initially thought it may be a kestrel but, as we closed in on one another, I saw its long bill and shorebird-like silhouette. The bird safely crossed the interstate and, at last sight, was zig-zagging along a chain of meltwater pools. Clearly, it was a common snipe.

Such rapid identifications are often achieved by experienced birders, who come to learn that the bird's shape, posture, song, behavior and natural setting will provide an accurate assessment in most cases. Waiting for the bird to perch quietly while you study its plumage is generally futile. So, next time you're out on the interstate, keep your eyes peeled for a snipe!

Tuesday, February 20, 2007

Cold Mud

We've been hoping for a break from this long, frigid winter and it arrived three days ago with highs in the 40s and 50s. The snow and ice have been melting but, unfortunately, the deep soil is frozen and the vegetation is not yet absorbing this wealth of moisture. So we end up with sloppy yards, muddy trails and flooded fields. Today, cold rain is adding to the mess.

Such is the landscape of late February and early March: plenty of moisture with no place to go. While these conditions may impede our activities, the temporary wetlands provide welcome rest stops and feeding grounds for migrant waterfowl. Snow geese should begin moving through Missouri any day now and, by March, the first wave of ducks will arrive. Time to break out the boots, ponchos and binoculars.

Monday, February 19, 2007

The Awakening

An omen of spring was sprawled on the railing of our deck this morning: a groundhog. His appearance was rather surprising after only two days of mild weather following six weeks of ice, snow and frigid temperatures. While he seemed to be enjoying his respite in the morning sun, this early riser may have to return to his winter slumber; the ground is still mostly covered with snow and there is little greenery to sustain him.

Groundhogs are one of our true hibernators; others include ground squirrels, marmots, many bats and some bears. These mammals "sleep" through the winter, sustained by layers of brown fat that they put on during the warmer months. They are also able to greatly reduce their metabolism, entering a coma-like state with a minimal pulse and respiratory rate. Should their energy stores run out before spring arrives, the animal will die. For the latter reason, arctic mammals cannot hibernate; the winter at their latitude is too severe and prolonged to permit survival. Even at temperate latitudes, some mammals, such as chipmunks, store food in their winter dens, awakening at intervals to restore their fat pads.

Sunday, February 18, 2007

Birders and Conservation

Usually introduced to birding by a relative or friend, the novice birder begins with a focus on backyard birds, content to fill the feeders and watch for new visitors. He soon graduates to local parks and nature preserves, learning that many species will not be found in residential areas. Spurred on by the joy of finding new birds, he begins to expand his range, using free weekends to travel about the State and planning vacations that take him to new birding territory.

Birdwatching has become big business. Special stores cater to the birder, offering premium seed blends, squirrel-proof feeders and high-tech spotting scopes. In like manner, travel companies offer packages that appeal to birders, spawning the industry of ecotourism.

But the conservation movement has benefited most from this avalanche of birders. The more we learn about birds, the more we appreciate the diversity of the natural world and the more we understand the importance of protecting natural habitat. And more than any other family of wildlife, these mobile creatures, which often winter and summer on different continents, teach us about the interdependence of ecosystems across this planet. Unless we take a global approach to conservation, our efforts will surely fail.

Saturday, February 17, 2007

Alberta Clipper

Alberta Clippers are relatively compact, high energy storms that drop down from central Canada and then race across the eastern U.S. Dragging a cold front with them, they usually produce high winds and brief, heavy snow. As they move eastward, backside flurries and strong, northwest winds can produce ground blizzards. However, unlike the big storms associated with Arctic and Pacific fronts, the clipper episode is usually over within 6-12 hours.

Clippers often develop rapidly and are thus hard to forecast. We had expected our first warm day in 6 weeks yesterday, awaking to cold sunshine and light winds. Turning on the tube, we were a bit dismayed to learn that an Alberta Clipper was diving southward through the Dakotas, heading our way. By noon the clouds were moving in and cold winds picked up from the west. A full-fledged snowstorm struck by early evening, producing high winds and a three-inch snowfall. Flurries and gusty winds were still around this morning but, by noon, the sun was breaking through and the clipper had moved on to the Tennessee Valley.

Friday, February 16, 2007

Exotic Terranes

During the evolution of our planet, the continents have moved about and changed shape, governed primarily by the opening and closing of oceans and seaways. Throughout this process, pieces of the continents have rifted away while other land masses have collided with their margins, welding themselves to the central cratons. These mobile pieces, known as exotic terranes, ride on the oceanic plates as they move from spreading zones to trenches.

Today, the continents are composed of central, "stable platforms" to which smaller terranes have been sutured. In North America, most of the southeastern Piedmont, all of the land west of eastern Utah, all of British Columbia and the entire State of Alaska have been added as a mosaic of exotic terranes. One of the more traveled land masses was the Alexander Terrane. After splitting from proto-Australia, 500 million years ago, it moved across the ocean, coupled with the Peruvian coast and then bounced along the western edge of North America before attaching to the northwest edge of Canada, 100 million years ago; it is now the southeast panhandle of Alaska. In like manner, Vancouver Island originated in the Southern Hemisphere, moved northward and, 50 million years ago, docked off the coast of British Columbia.

Today, new terranes are forming above oceanic hot spots and along subduction zones. Others are tearing away from their home continents; the opening of the Gulf of California is ripping the Baja away from Mexico and the East African Rift will eventually send a large chunk of that continent out to sea. Southern California is creeping northwestward along the San Andreas Fault and, after millions of years at sea, will eventually merge with western Alaska as the intervening oceanic plate disappears into the Aleutian Trench.

Thursday, February 15, 2007

Island Refuge

Marsupials are pouch-bearing mammals such as opossums, kangaroos and wombats. After fertilization, the fetus initially grows within the uterus where it is nourished by a yolk sack (rather than a placenta); within 4-5 weeks, the immature fetus must leave the uterus and make its way to the maternal pouch where it attaches to a nipple for another month or more of development. This system imposes a much higher risk for the marsupial fetus compared with the fetal risk of a placental mammal; thus, in areas where they both exist, placental mammals tend to be more successful and often displace the marsupials.

Marsupials first appeared in the Cretaceous Period, some 100 million years ago. Whether they first evolved in North or South America remains a subject of controversy; nevertheless, the dirth of placental mammals in Gondwanaland (the attached land masses of South America, Antarctica, Australia, Madagascar and India) allowed the marsupials to thrive and disperse.
When marsupials first appeared, Africa had just separated from South America and the latter would break from Gondwanaland in another 25 million years. India also broke away about 85 million years ago, drifting northward with its cargo of marsupial fauna. Australia separated from Antarctica about 55 million years ago, moving toward the northeast and beginning its long history as an island continent.

Antarctica drifted to the South Pole, killing off the vegetation and all terrestrial fauna. India would begin crunching into southern Asia about 65 million years ago, forcing up the Himalayas and permitting an interchange of species between these land masses; as discussed above, the placental mammals would soon dominate. About 3 million years ago, South America connected with North America as the Isthmus of Panama drifted into place; the marsupials of South America would soon compete with eutherians (placental mammals) moving down from the north.

Australia thus remained the lone refuge for marsupials, allowing them to spread and diversify across the continent without competition. It was not until man arrived, about 60,000 years ago, that conditions changed; a combination of hunting and the use of fire to clear scrub are thought to have triggered the demise of the larger marsupial species. An additional threat was the introduction of dingos, which likely arose from domesticated dogs, within the last 10,000 years. The spread of urban centers, ranching and other human activities continue to pressure the native fauna, as evidenced by the extinction of the marsupial wolf in the 1950s. Nevertheless, Australia remains the last great refuge for marsupial life.

Wednesday, February 14, 2007

The Nature of Love

It's Valentine's Day, the annual Holiday of Love, sponsored by the jewelers, florists and confectioneers of America. But love is such an ambiguous and overused word. We love our spouse, our kids, our family, our friends and our pets. We say we love spring, jazz, hockey or pizza.

Is love unique to humans? Does the lioness that risks her life for her cubs or the mother elephant who refuses to abandon her dead calf feel love? Does the faithful dog love his master? Most biologists would argue that these are purely instinctual behaviors.

So what is human love? The religiously-minded say that love is spiritual, that it eminates from God. The pure scientist proclaims that it is a product of genes and brain chemistry, arguing that romantic love is nature's way of ensuring the survival of our species. On the other hand, behavioral psychologists point out that we must love ourselves before we can love others and that deficient nurturing in early childhood may leave one incapable of accepting or expressing love.

It seems that love is a unique and multi-faceted human trait. We may not understand the nature of love but we know it when we feel it.

Tuesday, February 13, 2007

Italy and Africa

During the Permian Period, 250 million years ago, the continents merged into a single land mass, known as Pangea. Fifty million years later, during the Triassic, Pangea began to break apart as the Tethys Sea split Laurasia (the northern continents) from Gondwanaland (the southern continents). The land that is now Italy moved southward as part of Africa.

The Tethys Sea reached its maximal extent during the Jurassic Period, some 150 million years ago. As it began to close, Africa moved northward, splitting away from the other Gondwanaland continents and, 50 million years ago, rammed into southern Europe. The leading point of this collision was Italy; as it was shoved into the Eurasian plate, the Alpine Orogeny began, lifting the Pyrenees, Alps and Carpathian Mountains. For now, Italy is part of the European Continent, separated from Africa by the Mediterranean, a remnant of the Tethys Sea.

It is interesting to realize that Italy was part of Africa three times longer than it has been part of Europe. Furthermore, if the closing of the Tethys had aborted, Italy would have been part of Ancient Egypt rather than the seat of the Roman Empire.

Monday, February 12, 2007

The Winter Warbler

Warblers are small, colorful birds with thin beaks. More than 50 species summer in or migrate through our country but, since they feed primarily on insects, almost all winter in Central or South America. Only one, the yellow-rumped warbler, winters in the American Midwest.

As you might expect, this warbler is best identified by his yellow rump; he also exhibits a variable degree of yellow markings on his crown and sides. While most warblers are very active feeders, flitting among the thinner branches of trees and thickets, yellow-rumps are a bit less frenzied. On the larger size for warblers, they feed in the manner of chickadees and titmice and, like these songbirds, search for insect eggs and pupae during the winter months.

Yellow-rumped warblers breed in the coniferous forests of Canada and the western mountains of the United States. While they favor stands of pine or spruce in winter, they are often found in mixed woodlands and are fairly common in residential areas. Why these small insectivores, free to vacation in Mexico, choose to winter in the cold, gray Midwest is both mysterious and inspiring.

Sunday, February 11, 2007

February's Gift

February is a maligned month, not even given its fair complement of days. While we cherish the frosty nights of October and welcome cold and snow for the Holidays, many of us are tired of winter by the time February comes along; we see it as a gauntlet that we must survive in order to reap the rewards of spring.

But February teaches us patience as it inches us toward the season of renewal. The days are gradually lengthening, bird song is increasing, the earliest crocus tips are poking through the soil and, by the end of the month, tree frogs are chirping from the wetlands. It is best that we take this month day by day, savoring the slow transition from winter to spring. We live too fast as it is.

Saturday, February 10, 2007

Songs of Hope

Winter is nature's quiet season. Thunder is rare and the wind has few leaves to rustle. The raucous calls of crows, the shrill cries of blue jays and the honks of restless geese are among the few familiar sounds of winter. Sparrows chirp, chickadees and titmice offer a few notes, white-breasted nuthatches yank and Carolina wrens produce flurries of song but there is no steady choir to greet the day. The long, cold nights are gravely quiet, save the occasional hoot of an owl, the bark of a fox or the howl of a coyote.

Come mid February, things begin to change. Stirred by the lengthening daylight, neighborhood songbirds welcome the morning sun with a steadily growing chorus. Chickadees, titmice, white-throated sparrows, house finches and American robins provide the background melodies while male cardinals sing boldly from a perch in the sun. The Carolina wren has settled into a more regular and purposeful tune and even the blue jay has adopted a softer, musical voice. Within a few weeks, these songs of hope will be joined by the sad call of mourning doves and the hysterical chatter of flickers. The birds are assuring us that spring is on the way.

Friday, February 9, 2007

A Bad Rap

Like the cavemen on the Geico commercials, dinosaurs often get a bad rap. Any service or product that has gone out of favor or become obsolete is labeled "a dinosaur."

Yet, dinosaurs, as a group, ruled the earth for 160 million years and were remarkably diverse and successful. Historically portrayed as lumbering, dim-witted, cold-blooded brutes, we now know that they were warm-blooded creatures that had more in common with today's birds than with prehistoric reptiles. And while most species died out after the Chicxulub asteroid strike, 65 million years ago, others gave rise to avian lineages of the Cenozoic Era.

By comparison, man has roamed this planet for only 125,000 years. Who are we to view the dinosaurs as failed creatures?

Thursday, February 8, 2007

Geology on Edge

The Ancestral Rockies rose during the Pennsylvanian Period, when much of the Continent was covered with primordial swamplands and the first reptiles were evolving. Throughout the latter half of this Period and into the Permian, these mountains eroded to a flat plain. The shallow Sundance Sea covered the region during the Jurassic, followed by another seaway through most of the Cretaceous Period.

As the Age of Dinosaurs was drawing to a close, some 70 million years ago, the modern Rockies began to rise. The Precambrian core of these mountains pushed up through a layer-cake of Paleozoic and Mesozoic sediments, which eroded from the range as it continued to rise. Today, these overlying sedimentary rocks form a zone of ridges and valleys along the base of the Front Range foothills; the more resistent rocks form the ridges, tilting toward the mountain core, while layers of shale have eroded into valleys. The oldest rock layers lie adjacent to the foothills, with successively younger layers to the east.

Visitors to the Colorado Front Range can easily spot the "red rocks," outcrops of salmon-colored sandstone that adorn the lower foothills between Colorado Springs and Fort Collins. These spectacular rocks, part of the Fountain Formation, represent a layer of erosional debris from the Ancestral Rockies; once flat, they were fractured and tilted upward as the modern Rockies developed. East of the red rocks is a ridge of yellow-gray Permian sandstone, known as the Lyons Formation, and east of that ridge is the famous Morrison Formation, a valley of shale deposited in the Sundance Sea. Finally, east of this valley is the Dakota Hogback, a prominant ridge of Cretaceous sandstone, the remnant of beaches along the Cretaceous Seaway. As one might expect, the Morrison Formation and Dakota Sandstone are rich in dinosaur fossils.

Wednesday, February 7, 2007

Out of Africa

Modern DNA studies, coupled with decades of field work by anthropologists, have given us a fairly good understanding of early human migration. Man evolved in East Africa about 125,000 years ago, as the third glacial period of the Pleistocene (the Illinoian Glaciation) was drawing to a close. Over the next 50,000 years, humans spread throughout sub-Saharan Africa; their northward migration was likely impaired by expansion of the North African desert during this warm, interglacial period.

By the onset of the Wisconsin Glaciation, about 75,000 years ago, man had spread to the southern coast of Asia and, by 60,000 years ago, had reached southeast Asia and Australia. Lowering sea levels produced land bridges throughout the Indonesian archipelago but humans managed to cross a wide swath of the ocean to reach Australia. Japan was colonized by 50,000 years ago, presumably via a land bridge from the east coast of Asia. As the cooler, wetter climate caused the Middle Eastern deserts to retract, man spread northward into Europe and western Asia about 40,000 years ago; there he encountered Neandertals who had inhabited Eurasia for over 150,000 years (and who would disappear within 10,000 years of man's arrival).

Humans reached Siberia 30,000 years ago and crossed to North America via the Bering land bridge. Within another 10,000 years they managed to spread throughout the Americas; some populations likely moved down the Pacific Coast while others crossed through an interglacial corridor, east of the Rockies. Recent evidence suggests that a third population may have reached North America from Europe, hunting and camping along the North Atlantic Ice Shelf. Cuba and other Caribbean islands were colonized about 7000 years ago.

Polynesians set out to explore the Pacific at least 6000 years ago and colonized Samoa about 3000 years ago. Their continued explorations led them to the Marquesas Islands in 300 AD, Easter Island in 318 AD, Hawaii in 500 AD and both Tahiti and New Zealand about 800 AD. By then, only Antarctica remained untouched by humans.

Tuesday, February 6, 2007

The Snows of Tug Hill

The Tug Hill Plateau rises to the east of Lake Ontario, between Syracuse and Watertown. Home to the largest unbroken tract of northern hardwood forest in New York State, the Plateau is a layer cake of sedimentary rock which rose with the Adirondack Mountains, to its east; the Black River Valley separates the two regions. Since it tilts upward atop the Adirondack Precambrian dome, elevations at the west end of the Plateau average 350 feet while those at the east end exceed 2000 feet. Cold air blowing across Lake Ontario becomes saturated with moisture and, forced to rise up the Plateau, drops prodigious amounts of snow.

In this season of persistent lake-effect snowstorms, accumulations on the Tug Hill Plateau top the list, as usual. In fact, the higher elevations of the Plateau average over 200 inches of snow per year, the deepest annual snowpack in the eastern U.S. and an important source of fresh water for New York State. The Tug Hill Plateau also holds the eastern record for the greatest depth of snowfall in one day: 77 inches. Yesterday's snowfall of 4 feet was nothing to sneeze at either!

Monday, February 5, 2007

The Audacious Songster

Carolina wrens do not look like they belong in a Midwest winter. This small, rust-colored bird with a prominant white brow stripe and thin, down-curved bill, is reminiscent of those insect hunters that fill our backyards during the warmer months. And, indeed, this active, noisy resident does feed on insects, continuing to search the leaf litter for their eggs and pupae throughout the winter.

But Carolina wrens also consume seed and, like the much larger blue jays, tend to dominate feeding stations at times. Whether digging through the feeder or scavenging the ground, they show an aggressive flare, easily spooking the skittish sparrows as they move about with their thin, sharp bills. And their clear, loud song, delivered throughout the year, seems to send the message that they are not intimidated by anything, let alone the cold, snowy weather.

Sunday, February 4, 2007

Arctic Blast

The latest and perhaps last Arctic air mass has plunged into the heartland, dropping temperatures to seasonal lows. Much of the northern Midwest won't reach zero today and Chicago is expecting its coldest day in 11 years. Lake-effect snows have re-ignited along the lee side of the Great Lakes and central Florida will have highs in the fifties after deadly tornados, triggered by the cold front, ravaged the area. Here in Missouri, we expect a high of 20, despite sunny skies.

Meanwhile, Alaska is relatively warm as the jet stream is pushing mild air up from the Pacific. This warm front has displaced the Arctic air which, guided by a dip in the jet, has dropped into the lower forty-eight. Now that we are almost 6 weeks past the winter solstice, we can hope that the higher sun angle will begin to moderate the Polar conditions and make any further outbreaks less severe. As they say, time will tell.

Saturday, February 3, 2007

Precambrian Domes

Precambrian rocks form the basement of the Continental plates. By definition, these ancient igneous and metamorphic rocks formed between the earliest days of the Earth (4.6 billion years ago) and the onset of the Paleozoic Era (600 million years ago). In most areas, they are covered by thick deposits of sedimentary and volcanic rocks from the Paleozoic, Mesozoic and Cenozoic Eras and are only visible under one of three circumstances: where a river has cut a deep canyon through the overlying sediments (e.g. the Grand Canyon), where erosion (such as glaciation) has removed the overlying sediments (e.g. the Canadian Shield) or where these deep Precambrian rocks have been uplifted to form mountain ranges (e.g. the Rocky Mountains and the Blue Ridge Mountains).

In some areas, the uplift of the Precambrian rock has occured as a broad dome; the Adirondacks of New York, the Black Hills of South Dakota and the St. Francois Mountains of southeast Missouri are excellent examples. Following the uplift, the overlying sediments are eroded away and the Precambrian core is carved into a cluster of mountains by continued erosion. The layers of sedimentary rock that once covered the dome are still evident along its outer margin, usually forming "cuestas" that slope upward toward the mountains. The variable resistence of these sedimentary layers produces a topography of ridges and valleys that ring the dome of mountains. Satellite views of these areas illustrate the geomorphology especially well.

Friday, February 2, 2007

Settlers and Cardinals

When white settlers first reached America, northern cardinals ranged across southeastern and south-central North America and along coastal areas of Mexico. Most of the Northeast and Great Lakes region were covered with virgin forest and the cardinal is not a forest bird. Rather, cardinals inhabit thickets, open woodlands and the border zone of fields and forest.

As the settlers cleared forest for timber, agriculture and residential areas, the cardinals spread northward; over two centuries, their range expanded through the eastern half of the U.S. and into southern Canada. They have also migrated westward, following the chain of towns and cities that are spaced along the primary rivers of the Plains States. Over the past decade, cardinals have begun to appear in eastern Colorado, primarily along the South Platte and Arkansas Valleys, and, in recent years, have been spotted on the outskirts of Metro Denver. In the southwestern U.S., irrigation and suburban sprawl have enticed them northward from Mexico and they are now found in southeastern California, southern Arizona and southwestern New Mexico.

This is one case where a native species has actually benefited from the activities of man. While we need to protect as much wilderness and natural habitat as possible, we can also benefit wildlife by making our "developed" areas eco-friendly.

Thursday, February 1, 2007

A Real Winter

After a series of mild winters, we just experienced a more typical January. In fact, temperatures were below normal for most of the country throughout the month. Here in Missouri, a mix of sleet, ice and snow has covered the ground for three weeks and we've had very few days above freezing since the beginning of the year. Heavy snow has blanketed much of Colorado, unusual cold has damaged crops in California and ice storms have plagued the southern plains.

Those who dread winter have probably had a miserable month. I suspect that many of them have secretly welcomed the idea of global warming, thinking that they would soon have a perpetual summer. Of course, others, like power companies, plowing services and natural gas producers have benefited from the prolonged cold and heavy snows. Our fearless TV weathermen were among the big winners; after a dud of a hurricane season, they were able to fan out across the country, bringing us eye-witness accounts of sliding cars, toppled powerlines and frozen oranges.