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Showing posts from March, 2011

The Nature of Aftershocks

An earthquake occurs when pressure is released along a fault; this pressure builds up due to friction between two plates, whether related to direct compression, sideways scraping (e.g. the San Andreas Fault) or one plate dipping beneath the other (subduction). The sudden release of pressure and the resulting plate slippage transfers pressure to other points along that fault and to vulnerable sites on other intersecting faults.

In some locations this transferred pressure is of no immediate consequence while, in others, the additional pressure exceeds the tolerance of the plate friction, producing other earthquakes; these secondary quakes are commonly referred to as aftershocks. Following a major earthquake, there are always hundreds if not thousands of such aftershocks, many of which are too faint to be noticed; furthermore, each secondary quake produces its own aftershocks. While these subsequent events are less powerful than the inciting quake, they can be strong enough to produce…

Ocean Currents & Regional Climates

The surface currents of our oceans, which extend to depths of 1500 feet, are determined by wind patterns and the effect of Earth's rotation. In the Northern Hemisphere, the primary oceanic currents flow in a clockwise direction while, in the Southern Hemisphere, they move counterclockwise. Those moving from the Tropics toward the Poles are warm currents and those moving from the Poles toward the Equator are cold currents.

More that a mixing of oceanic waters, these currents have a significant impact on the climate of coastal land areas. The Gulf Stream, for example, carries warm water from the Gulf of Mexico and Caribbean toward the North Atlantic, significantly moderating the climate in Iceland and the British Isles; in like manner, the Japan Current, flowing from Southeast Asia to Alaska, warms the climate of coastal Alaska and British Columbia. Cold currents, such as the Humboldt Current along the west coast of South America, the Benguela Current along the southwest coast o…

A Raw East Wind

My walk to work this morning was into a chilly east wind. In this part of the country, an east wind is generally damp and uncomfortable, especially in early spring; its presence is associated with a cold front to our south, high pressure to our north and low pressure along the Gulf Coast.

Clockwise winds around the high pressure combine with a counterclockwise flow around the low, producing an east wind; since the low is also injecting Gulf moisture into the air, it is a raw wind, triggering showers or flurries as it rakes the Heartland.

Relief from this menacing wind and its cargo of moisture will come as the high pressure moves east and the southern storm moves up the Atlantic Seaboard. In concert, a ridge of high pressure will arrive from the west and our wind will shift to a southwesterly flow, ushering in warmer and drier air. Just another dip and climb on the roller coaster of a Midwest spring.

Journey to Swan Lake

Swan Lake National Wildlife Refuge spreads across the Glaciated Plain of north-central Missouri, just east of the Grand River Valley.Its mosaic of lakes, ponds, fields, riparian woods and interconnected wetlands is a magnet for migrant waterfowl and today's visit turned up an excellent variety.

Restless flocks of snow geese moved about the preserve while numerous ducks, coot, grebes and Canada geese gathered in the wetlands. A flotilla of white pelicans lined the northern shore of Silver Lake and wood ducks zigzagged through flooded timber at the south edge of the refuge. Northern harriers were especially common, hunting low across the grasslands, and a pair of bald eagles soared high overhead. Other sightings included red-tailed hawks, red-headed woodpeckers, killdeer, horned larks, meadowlarks and those ever-present red-winged blackbirds.

As is true with most field trips, the journey to and from Swan Lake was also of interest. Avoiding major highways, one gets a feel for the…

Rewards of Ugly Weather

This morning dawned cold and gray in central Missouri and the threat of chilly rain or wet snow was beginning to douse our spring fever. Nevertheless, I decided to make my weekly spring visit to Eagle Bluffs Conservation Area, on the Missouri River floodplain, and was rewarded by both solitude and a spectacular diversity of wildlife.

Carpets of purple henbit tried to adorn the landscape but grays and browns still ruled as winter had yet to abandon the valley. Near the entrance to this wetland preserve, two sandhill cranes, stained a tawny brown, foraged on a burned field with a noisy flock of killdeer. Throughout the refuge, coot, Canada geese and ducks gathered on the ponds, early shorebirds fed in the shallows and clouds of red-winged blackbirds moved across the fields. A tardy flock of snow geese weaved overhead, a pair of bald eagles cavorted in the cold, gray sky and white-tailed deer raced among the corn stubble, chasing off the morning chill. Once again, American white pelic…

The Early Swallow

Among the earliest of our summer birds to return to their breeding grounds, tree swallows usually appear in the American Midwest by mid March. First sightings are often of large flocks in the barren, drowned trees of reservoir backwaters, where they feast on insects rising from the lake or adjacent wetlands. While insects may be unavailable during periods of cold March weather, tree swallows supplement their diet with berries when necessary.

Though they arrive in large flocks, these swallows soon pair off to locate a tree cavity or nest box in which to raise their young; their aggressive behavior and attraction to blue bird boxes has interfered with efforts to protect those beloved songbirds. Once established at a nest site, tree swallows swoop across open fields, lakes and wetlands to snare flying insects; as they tilt in the sun, their iridescent blue-green back, contrasting with white underparts, makes identification easy. In addition, since their cousins (barn, cliff, bank and…

Vulture Traffic

The turkey vultures of Columbia, Missouri, have established a large colonial roost near the south edge of the MU campus. From our back deck, a mile northwest of the roost, I often see these graceful birds heading east during the hour before sunset, as they return to that site.

Like commercial jets on final approach, the vultures seem to follow a rather strict flight path and those arriving from the north or south merge into the same inbound lane. Since this scenario is not observed every evening, I must assume that their route of descent, like plane traffic, is determined by the wind direction. Though I have no direct evidence, I suspect that, given their highly developed sense of smell, the vultures are guided by the odor of their roost, carried on the wind; if that is the case, then they, like aircraft, land into the wind, an approach that yields more control from an aerodynamic point of view.

While the above musings may be off target, it is by simple observation that scientific …

The Battleground of Spring

By the middle of March, a higher sun and an unsettled jet stream have loosened winter's grip on the Heartland. Directing Pacific storms across central latitudes of North America, the jet opens the door for summer to make a comeback; ahead of each front, south winds push heat and humidity into the Midwest while, behind these atmospheric barriers, winter plunges back from the north.

Along the clash zone, where winter shoves itself beneath the sultry air, thunderstorms ignite and, as on human battlegrounds, the air erupts with flashes of light and the roar of explosions. This war of seasons will continue into mid June when the jet stream finally settles in Canada, winter retreats to the far north and summer reclaims the Heartland.

We humans, anxious for an end to winter's reign, tend to enjoy the balmy advance of summer and resent the counterattacks of winter. But it is this prolonged battle that yields the copious moisture of spring, a vital element in nature's verdant re…

Surveillance Season

March is the month when Midwestern naturalists, including myself, begin our daily surveys of the changing flora and fauna on our property. The lengthening days, milder temperatures and thawing soil trigger a range of events that lead from the demise of winter to its resurgence, late next fall. Over the coming weeks, greenery will spread from the lawn to the treetops, flowers will increase in number and variety, insect populations will explode, summer birds will return from their winter haunts, toads will trill on balmy nights and newborn mammals will leave their dens to explore an inviting yet dangerous world.

Each day brings a subtle change as we watch the season unfurl and anticipate the luxurience of May and June. For now, we are content with the flowers of bulb plants, forsythias and early magnolias and welcome the fragrance of warming soil. We relish the intensity of bird song, watch the robins build their nests and take note of courtship behavior in our other avian residents…

Cerebral Override

One would think that we humans, endowed with a large, complex brain, would be more aware of our environment than "lower" forms of life. In fact, the opposite is generally true.

Other animals, acting on instinct and focused on survival, rely on their senses for the detection of prey and for protection from predators. Unencumbered by cerebral distraction, they are highly aware of visual, auditory, vibratory and olfactory clues that eminate from their surroundings. Humans, on the other hand, prone to analysis and subject to rumination, are constantly bombarded by thoughts; every sound, sight and smell is likely to trigger a memory and our natural senses cannot protect us from the worry, regret and anticipation that often cloud our mind.

While we will never be as keenly aware of our environment as many of our wild neighbors, it is worth the effort to immerse ourselves in nature and attempt to soak in its bounty. A secluded wilderness, far from the trappings of human commerce…

Coot Invasion

On this first astronomical morning of spring, I decided to visit Eagle Bluffs Conservation Area, southwest of Columbia, my favorite location in Central Missouri. As expected, waterfowl were abundant and the annual coot invasion was beginning to peak.

Closely related to rails and gallinules, American coot are the most common and most aquatic members of their family. Easily identified by their chunky, dark gray body, white bill and jerky swimming style, coot often mingle with ducks and grebes. Gathering in large, amiable flocks during the spring and fall migrations, these comical birds feed on surface vegetation, dive to reach bottom plants and forage for seeds, waste grain and grasses along lakeshores and levees. Since their flesh is not valued by hunters, coot tend to be less skittish than other waterfowl; when startled, they patter across the surface to escape and are rarely observed in flight.

American coot are permanent residents in southeast Missouri and breed on wetlands thro…

Natural Forces & Human Disasters

As we have observed in Japan over the past week, natural forces can devastate human populations. Indeed, 74,000 years ago, the eruption of the Toba Supervolcano, on Sumatra, nearly annihilated our species.

Nevertheless, these events, including earthquakes, tsunamis, hurricanes, floods, droughts, wildfires and other so-called natural disasters have been instumental in shaping our planet. Tectonic forces and climate fluctuations have produced our scenic landscapes and laid the groundwork for the evolution of life. Without the balance of energy that these events insure, we would not be here to witness nature's handiwork.

While these vital natural forces are often disasterous for humans, we have a habit of putting ourselves in harm's way. We build cities on fault lines, along subduction zones, on floodplains, near volcanoes and on barrier islands. Our short life span and relatively brief collective memory lead us to assume that projections of potential disaster are just scien…

Florissant Fossil Beds

In the western foothills of the Pike's Peak massif, petrified stumps and logs of giant sequoias lie amidst groves of ponderosa pine and outcrops of Precambrian granite. Protected within the Florissant Fossil Beds National Monument since 1969, these fossilized trees are the highlight of one of the more complete time capsules of an Oligocene ecosystem on our planet.

About 35 million years ago, volcanic eruptions in the Thirty Nine Mile Range, southwest of Florissant, Colorado, sent ash clouds and mudflows across this region, quickly burying and preserving a diverse collection of plant and animal life. Fossils of these organisms are now encased in shales, mudstones, silstones and volcanic tuff, some of which settled in Lake Florissant, created by the mud flows.

The fossil beds of this National Monument are especially famous for the fragile impressions of insects, spiders and leaves that were captured within the volcanic deposits. Access to the Monument and its 14 miles of hiking t…

Disasters & Miracles

In the course of major disasters, whether natural or man-made, there are always instances of improbable survival. The news media, playing on human emotion and inclined toward melodrama, often refer to such events as miracles.

Religious persons, looking for the hand of God in their lives, accept this designation while ignoring why God permitted the disaster to unfold in the first place. Others, enamored with the concepts of fate and destiny, are also quick to accept a mystical cause for these events. More thoughtful humans, an unfortunate minority, realize that there will always be some survivors amidst the widespread carnage and attribute their good forture to a combination of luck and the hard work of skilled rescuers.

Regardless of how we might view these events, we must understand that those who survive disasters may be burdened by both the scourge of post traumatic stress disorder and by the opportunitists who exploit their survival. Their ordeal often leads to unwanted celebr…

Japan's Quake & Tsunami

Northern Japan lies on a southward projection of the North American Plate and, off its east coast, the Pacific Plate is subducting beneath it; friction along this subduction zone pulls down the edge of the North American Plate and, eventually, the Plate rebounds, triggering an earthquake and lifting the overlying ocean.

Today's massive quake, the most powerful in Japan's recorded history, measured 8.9 on the Richter scale and sent a wall of water across the northeast coast of that island nation. While most destructive close to the earthquake, the tsunami will propagate in all directions, affecting islands and coastlines along and across the Pacific. The axis of maximum energy is projected to pass through Hawaii and toward South America but tsunami warnings have been posted from Alaska to New Zealand, including much of the U.S. West Coast.

Widespread destruction and numerous deaths will surely be reported in Japan and the effects of this powerful earthquake will no doubt prod…

Chiseling the African Plate

During the Permian Period, some 250 million years ago (MYA), future Africa was encased within the combined land mass of Pangea. Then, about 200 MYA, the Tethys Sea began to open, splitting Pangea from east to west and separating the northern continents (Laurasia) from the southern land masses (Gondwana); future Africa was part of the latter.

About 160 MYA, Madagascar split from southeast Africa and, 10 million years later, the Atlantic began to open. The combined mass of Africa and South America rifted from Antarctica about 140 MYA and the final separation of Africa and South America occured 100 MYA as the Atlantic Rift spread southward. As the Indian Ocean widened, some 50 MYA, the Tethys Sea began to close and Africa drifted northward to collide with the Eurasian Plate, crumpling up the Alps; the Mediterranean Sea is a remnant of the Tethys. Finally, the East African Rift began to form about 40 MYA; as the Red Sea opened, the Arabian Plate split from Africa and, today, continues…

The Great Range

After splitting from tropical Antarctica, the sub-Continent of India drifted to the northeast and, some 70 million years ago, began to collide with southern Asia. This collision, which continues today, has lifted the Himalayas, the youngest and highest mountain range on our planet. Stretching for 1500 miles, from northern Pakistan to Arunachai Pradesh, the northeasternmost province of India, the Himalayas are composed of three parallel ranges, increasing in elevation from south to north.

Capped by Mt. Everest, 29,035 feet (and rising), the Himalayas contain more than 100 peaks that exceed 23,500 feet and harbor the 15 highest summits on our planet. The perpetual snows and 15,000 glaciers of the higher Himalayas feed massive river systems, including the Indus of Pakistan and the Ganges and Brahmaputra Rivers of India and Bangladesh; the latter two rivers merge to empty into the Bay of Bengal, producing the largest river delta on Earth.

More than a spectacular wall of mountains, the …

The Chill of March

Here in the American Midwest, late winter and early spring rarely bring the coldest temperatures of the year but often harbor some of the most uncomfortable weather. An unsettled jet stream, undulating across the country, creates an alternating influx of mild and chilly air; the collision of these air masses assures copious precipitation, usually in the form of wet snow or cold rain.

The combination of high humidity, cool air and breezy conditions is often more chilling than the dry, frigid air of mid winter, especially when it arrives on the heels of a warm interlude. In the heart of winter, we adjust to the cold and come to appreciate any weather that climbs above the freezing point; by early spring, periods of mild weather have diminished our tolerance and the effects of each cold spell are magnified.

Of course, our impatience also augments the chill of early spring. We anticipate the warm, fragrant, colorful days of April and May and the month of March represents an unwelcome b…

Premature Pelicans

Arriving at Eagle Bluffs Conservation Area early last evening, my wife and I spotted a flock of white birds rising in the distance. Their size and flight pattern suggested American white pelicans but it seemed a bit early for their presence; afterall, those majestic birds usually move through Missouri from late March through mid April. Nevertheless, a quick check with the binos confirmed their identity as thirty or more of the pelicans glided above the edge of the floodplain.

Moving southward through the refuge, we encountered a large variety of ducks, scattered flocks of Canada geese, groups of ring-billed gulls, rafts of American coot, a few bald eagles and a fair number of great blue herons. We also came across more flocks of white pelicans, sailing above the wetlands or resting in the shallows. Then, near the south end of preserve, we discovered a huge congregation of the pelicans (at least 200-300) that had settled along a large lake, easily the largest flock that I have ever…

The Scourge of Polypharmacy

During the first few decades of television, tobacco ads were beamed into American homes, encouraging all of us to indulge. Thanks to the efforts of public health groups and despite the power of the tobacco lobby, this advertising has since vanished from the airwaves. Alcohol consumption, on the other hand, still receives plenty of encouragement, highlighted by joyous partiers and tempered by the hypochritic admonition to drink responsibly.

In recent years, the American pharmaceutical industry has decided to bypass physicians and market their products directly to the public. We are now deluged with their advertisements which depict happy, upscale drug consumers while, in the background, a narrator lists the numerous potential side effects of their miraculous pill. Such irresponsible advertising, which ignores the complexity of medical therapy, exacerbates the perception that there is a quick remedy for every ailment and that bad lifestyle choices can be erased with a prescription d…

Geophyte Season

The appearance of hyacinths and crocuses, in late winter, is a welcome sight to gardeners and heralds the onset of geophyte season in the American Midwest. Geopyhytes are perennial plants that harbor underground, nutrient-storage structures that permit survival during periods of prolonged cold or drought and fuel the rapid development of stems, leaves and flowers when soil conditions recover.

There are three primary types of geophytes: those that produce bulbs, corms or tubers. Bulb plants, including hyacinths, tulips, narcissus, lilies, onions and others, possess a cluster of specialized leaf scales which surround the basal stem and store nutrients. In most species, a protective tunic envelops these scales and, in all species, a basal plate gives rise to the root system. Corms are starchy stem structures which sit vertically beneath the soil; crocuses and gladiolus species utilize this form of nutrient storage. Finally, tubers are thickened, starch-containing, horizontal structu…

Morning Snows

Yesterday morning, a flock of snow geese flew over our neighborhood, catching a southeast breeze in the cold, clear sky. Nearly invisible in the first glow of dawn, their distinctive calls belied their presence and gradually faded into the darkness as the flock moved on to the north.

Having spent the night on the Missouri River floodplain, these determined migrants will make several more stops in the Upper Midwest and Canada before arriving on their Arctic breeding grounds. Just three months ago, the snow geese crossed Missouri on their way to coastal marshlands of Louisiana and Texas, where they spent the depths of winter.

Watching them move southward in late November and early December, we were quick to envy their freedom, longing to follow them to the balmy coast. Now, as the early signs of spring spread across the Heartland, we are less inclined to be jealous, knowing that these hardy birds are flying toward the last stand of winter. Nevertheless, we admire their fortitude and…

Recovery

While birdsong has steadily increased since mid February, snow geese have departed for their summer home and crocuses have brightened the flower beds for the past week, it is in March that the tide of spring begins to accelerate. Longer days and a higher sun take a toll on winter's grip, thawing the soil, greening the lawns and drawing sap into the expanding buds of shrubs and trees.

Robins reappear on our suburban carpets, cottontails produce their first litter of the year, forsythias and red maples start to bloom and great horned owlets peer from their bulky nest. As the month progresses, migrant waterfowl fill our lakes and ponds, Canada geese nest in our marshlands, the purple haze of henbit adorns our floodplains and the greenery of spring climbs from the shrubs to the treetops.

This annual recovery from a frozen landscape is a welcome sign for winter weary humans; but, while many view this season as nature's rebirth, her cycle has never shut down. The colder months ma…

March & November

March and November are not beloved months in the American Midwest. While November's image is rescued by the Thanksgiving Holiday and March appeals to college basketball fans, both months are known for their gray skies and cool, wet, blustery weather. After all, both are closely linked to winter and we humans, natives of the Tropics, tend to favor the warm, sunny months.

Nevertheless, March and November have much to offer for the naturalist. Waterfowl migrations peak during these months and wild mammals, stirred by the chill but unencumbered by harsh winter weather or oppressive summer heat, are especially active and conspicuous. And, contrary to popular perception, both months offer plenty of mild, sunny days on which to observe the changing landscape and the abundant wildlife.

This morning, with Venus and a crescent moon paired in the southeast sky, dawn arrived clear and cold. As I walked to work, a barred owl called in the distance and the mellow tune of mourning doves waf…