Wednesday, January 30, 2013

The Tehachapi Range

The Tehachapi Mountains stretch for almost fifty miles across Southern California; oriented southwest to northeast, this relatively low range connects the Transverse Ranges (on the north rim of the Los Angeles Basin) with the southern end of the Sierra Nevada Range.  Of equal significance, the Tehachapi Range forms a topographic wall between California's Central Valley, to its northwest, and the Mojave Desert, to its southeast.

These mountains formed due to compression and uplift along the Garlock Fault, which runs along the southeast edge of the range and joins the San Andreas Fault near Frazier Park; there, the Tehachapi Mountains merge with the Transverse Ranges.  At the northern end of the Tehachapi Range, the Barstow-Bakersfield Highway crosses Tehachapi Pass, elevation 4000 feet, within a broad parkland occupied by the town of Tehachapi.  South of this town is Tehachapi Mountain Park and, to its south, is Double Mountain, elevation 7993 feet, the highest summit in the range.

While elevations across the Tehachapi Mountains are relatively modest, ranging from 4000 to almost 8000 feet, this range plays a significant role in the ecology of Southern California.  Prevailing northwest winds carry Pacific moisture down the Central Valley, which is closed off by the Sierra Nevada to the east, the Tehachapi Mountains to the southeast and the Transverse Ranges to the south; in their rain shadow, to the southeast, is the vast Mojave Desert.  The Tehachapi Mountains themselves, covered primarily by grasslands, oak savannas and, at the highest elevations, coniferous forest, represent an important wildlife corridor between the Sierras and the Transverse Ranges; the Nature Conservancy, in concert with local and other national conservation organizations, is thus working to protect natural habitat along the crest of the range.  Finally, the relatively low Tehachapi ridge is essentially a wind funnel between the Central Valley and the Mojave Desert, offering an ideal setting for wind farms.

Tuesday, January 29, 2013

A Trough of Winter

A broad dip in the jet stream encompasses the western half of the U.S., bringing much needed snow to the mountains and the Front Range urban corridor.  Its leading edge crossed the Colorado Piedmont yesterday afternoon, producing a sharp contrast between the spring-like morning and the wintery evening.  Intermittent snow fell through the night and has left about 4 inches of white gold on our Littleton farm; following almost two weeks of warm, dry weather, the precipitation and seasonal temperatures are more than welcome.

Ahead of this trough, Gulf air has swept northward across the Southern Plains and Midwest, bringing a dose of summer in mid winter.  As the cold front approaches, strong thunderstorms (some tornadic) will ignite in that warm, humid air, stretching from east Texas to the Ohio Valley and southern Great Lakes.  In the coming days, the trough of winter is expected to flatten out across the country, restoring seasonal conditions to most regions and pushing mild air back to the Gulf Coast.

While gyrations of cold and warm air (due to atmospheric troughs and ridges, respectively) are common in spring and fall, the current scenario has, in the past, been relatively uncommon in the middle of winter when the jet stream remained stable across the southern U.S.  However, as our climate continues to warm, an unstable weather pattern, characterized by dramatic shifts in temperature and potent storm systems will likely stretch through winter as well.

Monday, January 28, 2013

Cassin's Finch

A close relative of the purple finch, Cassin's finch inhabits open, coniferous forests of the Mountain West.  The male, which obtains his reddish coloration during his second breeding season, is best distinguished from the male purple finch by his well-demarcated, bright red cap, his narrower beak and a less intense rosy wash on his chest.  Females and first year males are nearly indistinguishable from female purple finches but have a narrower bill and a less prominent white eye stripe.

Cassin's finches usually feed on the ground and are often seen along mountain roads; they consume a variety of seeds, nuts, fruit and buds and will also feed on insects during the warmer months.  Their nest is placed on the outer branch of a conifer and 3-6 eggs are produced each year.

Primarily summer residents in the Pacific Northwest and Northern Rockies, Cassin's finches inhabit Colorado throughout the year and may be found from the ponderosa parklands of the upper foothills to the stunted forest of timberline; indeed, they are one of the more common species to be encountered at the alpine treeline, which occurs near 11,500 feet in our State.  In winter, some Cassin's finches migrate to the mountains of the Desert Southwest and Mexico while others adhere to vertical migration, moving to lower elevations; during the colder months, variable numbers of these finches turn up at feeders along the Colorado Piedmont, usually scavenging fallen seed in the company of juncos, doves and other ground feeders.


Sunday, January 27, 2013

Booming Ice

After more than a week of warm days and cold nights, the Colorado Piedmont lakes have been especially noisy.  The sharp pops, high-pitched whines and mellow, kettle drum sounds are produced by the surface ice as it contracts, expands and vibrates.  As one might expect, the symphony is most pronounced during the morning and evening hours, when the ambient temperature is most rapidly changing.

Anyone who has used ice-cube trays or forgot to retrieve a can of soda from the freezer knows that water expands when it freezes.  In fact, it increases in volume by 9%, exerting tremendous pressure on its container.  Affected by other factors as well, including currents, water depth, the age of the ice, snow cover and fish activity, lake ice is often in a state of flux, characterized by fractures, compression, scraping, heaving and splintering, among other pressure induced phenomena.  The various noises are the result of pressure release, producing a sudden thunder clap or sending more subtle vibrations through the ice sheets.  While this "booming" does not necessarily portend danger for those who ski, hunt or fish on the ice, it certainly makes most of us wary, especially after an extended period of mild weather.

In many ways, the physics of lake ice mimics that of plate tectonics.  While the latter is driven by the opening and closing of oceans (induced by heat transfer within the mantle), the rearrangement of lake ice occurs in response to the freeze-thaw cycle.  In both cases, solidified segments (crust or ice) are subjected to rifting, compression and lateral friction, producing zones of uplift, thinning, faulting and overthrust.  And though the process of plate tectonics is far more gradual than the gyrations of lake ice, the periods of pressure augmentation far exceed the brief but dramatic rupture events (booming and earthquakes).

Saturday, January 26, 2013

Cuomo's Nod to Nature

According to an article in the New York Times, Governor Cuomo of New York has proposed using Federal relief funds for Hurricane Sandy to assist coastal residents with storm-proofing their homes or to encourage them to relocate to safer areas by purchasing their damaged properties.  For naturalists, and for the American taxpayer, this is a welcome and refreshing approach.

Too often, the mantra "we will rebuild" follows such natural disasters and the tragedy-stricken residents are praised for their courage and resilience.  Yet, we humans have long placed ourselves in harms way, building on floodplains, barrier islands, coastal surge zones and fire-prone mountainsides.  While that freedom should not be denied, society cannot guarantee protection from the forces of nature and cannot be asked to fund re-construction in areas of high risk.

Hurricane Sandy may be a once in a Century event or a similar storm may strike next year.  As our global climate continues to warm, most meteorologists and climatologists predict that intense storms will become more common; this includes tropical cyclones as well as inland systems that produce flooding, tornadoes and blizzards.  To develop or rebuild on floodplains, whether coastal or riverine, demonstrates blind faith or naivete that invites future tragedy.  As Governor Cuomo so wisely expressed, there are certain landscapes that belong to nature and we exploit them at our own peril.

Friday, January 25, 2013

Buffleheads

Buffleheads are a favorite of many birders; even I, a healthy adult American male, must agree that they are cute.  These small ducks with their round heads, short bills and attractive plumage are always a joy to encounter.  Usually seen in pairs or small groups, buffleheads are among the few ducks that are monogamous, at least for several years at a time; despite their size, they are also among the longest lived of our waterfowl, sometimes surviving 15 years or more.

Residents of the vast Northwoods, from Alaska through Canada and southward into the Pacific Northwest, buffleheads favor woodlands along rivers and lakes where they nest in abandoned woodpecker holes, especially those of northern flickers.  Broods of up to 18 ducklings are cared for by the female and initially feast on insects or aquatic plant material at the surface of the water; adults dive for a wide variety of aquatic invertebrates and may also consume seeds.  By mid autumn, buffleheads disperse for wintering grounds along the coasts of North America or on inland rivers and reservoirs of the Lower 48; they may also turn up in eastern Siberia, Japan or Western Europe.

Since most of the ponds and lakes remain frozen along the Front Range, buffleheads have been especially common on the South Platte River this week, mingling with common goldeneyes, lesser scaup and hooded mergansers.  They will grace our region until early April when longer days and rising temperatures send them back to their northern homeland.

Thursday, January 24, 2013

The Society Islands

The Society Islands of the South Pacific mirror the Hawaiian Chain, 2700 miles to their north.  They too are a linear archipelago that formed (and continue to form) above a mantle plume, commonly known as a hotspot.  As the Pacific Plate moves to the northwest, a volcanic ridge forms above the hotspot and the islands represent high points along that ridge; there are 14 named islands in the Society Islands chain.

The youngest of the Society Islands, Mehetia, ESE of Tahiti, began to form about 500,000 years ago and continues to enlarge.  Tahiti, composed of two shield volcanoes, formed about 1 million years ago while Maupiti, the oldest of the eight primary islands (and thus at the northwest end of the chain) is about 4.6 million years old.  By comparison, the primary chain of the Hawaiian Ridge has been forming for almost 40 million years; in addition, the Hawaiian hotspot is much larger, igniting volcanism above the surface over a span of 2-3 million years (e.g. Maui, 2 million years old, is still at risk for volcanic activity while Tahiti, 1 million years old, is safely out of range of its parent hotspot).  Finally, the Hawaiian hotspot has been active for at least 80 million years while the Society Islands plume apparently formed about 5 million years ago.

As tropical volcanic oceanic islands age, the central cone(s) erode and eventually disappear beneath the sea, leaving only the coral reef that encircled the island.  Known as atolls, they are found at the leading edge of the volcanic chain (far from the hotspot); they too will disappear over time, leaving the remnant neck of the volcano, known as a seamount, far below the surface of the sea.

Wednesday, January 23, 2013

The Guiana Shield

Two billion years ago, the Continent of Columbia included what are now the Amazonian Platform and the West African Craton in addition to other land fragments.  Three hundred million years later, a thick layer of sandstone was deposited across what would become the northern section of the Amazon Platform, likely eroding from an adjacent mountain range; today, this 1.7 billion year old Precambrian sandstone formation is known as the Roraima Plateau.

When Pangea formed, late in the Paleozoic Era, Columbia was incorporated within its mass.  Then, as Pangea rifted apart during the Triassic (about 220 MYA), Columbia became part of Gondwana (the massive southern Continent); when the Atlantic Ocean began to open during the Jurassic (150 MYA), the West African Craton was split from the Amazonian Platform.  Breaking from Gondwana late in the Cretaceous (about 70 MYA), South America drifted westward and, throughout the Cenozoic Era, tectonic forces have continued to shape the Continent.  The Amazon Graben produced the valley of the Amazon River, splitting the Amazon Platform into northern and southern sections (the Guiana and Brazilian Shields, respectively).  The Guiana Shield now covers northeastern South America, from eastern Venezuela and southeastern Colombia to the Atlantic Ocean; its northwestern edge is bordered by the Orinoco River Valley while the Amazon River Valley forms its southern border.  The numerous tributaries of these rivers (and of other coastal streams) have eroded the Guiana Shield, leaving highlands sculpted from the Roraima Plateau; among these are tall mesas known as tepuis, most numerous across western portions of the Shield.  Cenozoic sediments, eroded from the Guiana Shield, now fill upper segments of the Orinoco and Amazon Basins, as do volcanic desposits from the Andes to the west.

Today, the Guiana Shield is covered by one of the most extensive and least disturbed tropical rain forests on Earth, home to a spectacular diversity of plant and animal life (including more than 20,000 species of vascular plants).  Its magnificent topography, the product of torrential rains acting on ancient Precambrian rock, is renowned for its numerous waterfalls; among these is Angel Falls in Venezuela, the tallest cascade (3212 feet) on or planet.

Tuesday, January 22, 2013

Too Warm, Too Dry, Too Soon

While ponds and lakes remain frozen along the Front Range and the brown landscape speaks of winter, a mild, southwesterly wind pushed afternoon highs above 60 degrees F today and this balmy flow is expected to persist for most of the coming week.  Frigid air and lake-effect snows may plague the eastern U.S. but it feels like spring here in Metro Denver.

Of course, this pleasant weather is not altogether welcome in light of our persistent drought and meager snowpack.  Unfortunately, a high pressure ridge over the Great Basin is deflecting Pacific storms to the north, taking them across the Northern Plains before they dive through the Midwest.  As a result, heavy snow, vital to Western ecosystems, has been limited to the Pacific Northwest and Northern Rockies, increasing concerns about water supply throughout the American Southwest and depriving Colorado ski areas of their famous powder.

Snow has essentially disappeared from the Colorado Piedmont and, even in the foothills, is confined to the shaded, north-facing slopes..  Unless the weather pattern changes in the coming months, bringing white gold to the High Country, wildfires may once again threaten the State.  While many enjoy this early spring, we truly need a heavy dose of winter.

Sunday, January 20, 2013

The Painted Desert

The entire Colorado Plateau, from Dinosaur National Monument in northwest Colorado to the San Rafael Swell in central Utah and southward to northern Arizona and northwestern New Mexico, might be called a painted desert.  Its colorful strata of late Paleozoic and Mesozoic sediments, sculpted into scenic canyons, buttes and mesas by the Colorado River and its tributaries, reflect the bright sunshine of that semiarid landscape.

Officially, however, the Painted Desert is a swath of northeastern Arizona that runs along the eastern edge of the Little Colorado River Valley, northeast and east of Flagstaff.  Named for its colorful badlands of the Chinle Formation, this scenic terrain arcs for more than 150 miles, from the eastern edge of the Grand Canyon to the vicinity of Petrified Forest National Park, east of Holbrook.  The banded strata of the Painted Desert are composed of siltstones, sandstones and volcanic mudstones (primarily bentonite), deposited in the late Triassic Period (about 210 million years ago) as Pangea began to rift apart; the colors result from hematite and other minerals within the varied layers of sediment.  Since their deposition (and especially during the wet climate of the Pleistocene) the Chinle Formation has eroded into a maze of hills and valleys; in some areas, a resistant cap of sandstone protects the soft, underlying sediments, producing buttes and mesas.

Almost all of the Painted Desert lies within the Navaho Nation and large portions have no road access.  This fascinating and beautiful landscape is best observed in the vicinity of Cameron (on U.S. 89), from Arizona 87, northeast of Winslow, and at Petrified Forest National Park, east of Holbrook.

Saturday, January 19, 2013

Te'o and Us

Whether Manti Te'o, the star linebacker for Notre Dame University, was the victim of a cruel hoax or was, to some degree, complicit in his dead girlfriend saga will be of little consequence to human society.  Of more significance in this bizarre tragedy is our rush to anoint heroes (usually for our own benefit and gratification) and then to discard them without ever truly understanding those individuals.

The initial revelation that Te'o's girlfriend had died of leukemia, just as his national celebrity was taking shape, was grasped and exploited by the sports media, Notre Dame and fans across the nation though few made any effort to investigate the facts.  Now that we know his online girlfriend did not exist, we cannot wait to ridicule our American hero, distancing ourselves from this once magical figure; of course, we know little about the details, including the personal factors that may have made Te'o especially vulnerable to the hoax and/or willing to participate.

Regardless of what facts may eventually surface, Manti Te'o has already lost his hero status in the eyes of the public and has now been labeled either a conniving self-promoter or an immature buffoon.  Te'o must live with the consequences of his mistakes and the rest of us must acknowledge our misguided tendency to anoint heroes based on superficial information and then punish them when they prove to be all too human.

Friday, January 18, 2013

Winter Dusk

Our farm in Littleton, Colorado, sits on the west wall of the South Platte Valley and commands a broad view to the east.  At dusk, I often go out to enjoy the vista and to watch the avian commuters as they move across the evening sky.

Today, after a sunny, mild January day, the winter traffic was typical.  Small squadrons, moderate skeins and large flocks of Canada geese were scattered above the horizon, moving from their feeding grounds to large reservoirs along the South Platte Valley; there they will spend the night, safe from attack by predators.  In like manner, ring-billed gulls cruised across the darkening sky, also headed for community roosts on the ice.  Joining these evening commuters were smaller flocks of ducks, including mallards, gadwall, green-winged teal and redheads.  Seemingly out of place (though common) in the Colorado winter sky, a great blue heron flapped toward the river, its stately form and slow, steady wingbeats conveying a specific flight plan, as controlled as the jets that drifted toward DIA.

Closer to home, the sight and distinctive calls of collared doves dominated the scene, paired off and settling in the treetops to catch the last rays of the sun.  Northern flickers, house finches, common bushtits and a lone Townsend's solitaire also moved about our property as a half moon glowed overhead and our mother star dipped behind the Rockies.  Just another glorious dusk along the Front Range; within hours, the night shift would rule the farm.

Thursday, January 17, 2013

Coyotes on the Farm

Over the past year, coyotes have successfully extirpated the red fox from our Littleton, Colorado, farm and are now using their abandoned den beneath our barn.  Last night, just after midnight, the pack began to yip and howl, a call of the wild not terribly welcome in suburban America.  After all, coyotes are known to prey on cats and small dogs and, in some cases, might pose a threat to young children.

Coyote packs consist of a dominant pair (the alpha male and female), young female offspring and the occasional stray that is welcomed into the group; male offspring of the adult pair seek their own territory within 9 to 12 months of birth and coyotes of both genders are sexually mature by one year of age.  Mating occurs in mid-late winter and a litter of up to 19 pups is born by late spring; mortality is very high during the first year of life but enough survive to support a growing coyote population that now ranges across all mainland U.S. States, Canada, Mexico and Central America, including urban areas.  Their success is due to a number of factors, including their intelligence, adaptability and omnivorous diet, which includes small mammals, waterfowl, game birds, reptiles, fruit, nuts, carrion and edible human trash; coyotes are also known to interbreed with wolves and feral dogs.

Whether we will be able to host the coyotes on our modest-sized, suburban farm remains to be seen.  Their nocturnal howling and their taste for small pets might force our hand but, for now, we'll let them control the mice and voles.

Tuesday, January 15, 2013

Downslope Rescue

After enduring frigid, Arctic air for much of the past week, Colorado's Front Range urban corridor is about to be rescued by a down-sloping, southwest wind.  Actually, the wind shift developed early this morning as the cold, low pressure trough pushed off to the east and a dome of high pressure developed over the American Southwest.

While the effect of this wind shift was visually evident today, scouring the haze from the Piedmont and producing crystal-clear views of the Front Range peaks, a persistent cloud deck limited the warming effect of the downslope flow and afternoon highs topped out in the low 30s (F).  Produced by the pressure gradient between high pressure to our southwest and low pressure to our ENE, the southwesterly winds compress, dry out and heat up as they descend from the Continental Divide and, over the next few days, will produce sunny skies with afternoon temperatures in the fifties.  In fact, our overnight lows will be 2-3 times the Fahrenheit value of our recent afternoon highs.

Meanwhile, west of the Divide, these same winds are up-sloping and the Arctic chill persists; while Metro Denver basked in 30 degree heat this afternoon, Grand Junction shivered in the single digits.  By contrast, when upslope snowstorms strike the Front Range corridor in March and April, the cities on the western slope receive a downslope flow and enjoy sunny, warm conditions.

Monday, January 14, 2013

Jury Duty

There are few human endeavors that expose our nature better than jury duty.  Gathering with a large number of strangers, all responding to a summons from city or county government, one is inspired by the respect that most Americans have for our justice system, however flawed it may appear at times.

Once underway, the culling process highlights the many personalties within the group.  Some, often with good reason, seek an early departure, siting other responsibilities.  Most of the rest are caught between the hope for exclusion and the potential thrill of participation, not to mention the emotional reward of being selected (a flashback to childhood pickup games).  The subtle maneuvers of the prosecuting and defense attorneys were also of interest, combining attempts to instill their own point of view while seeking out those who pose a threat to their cause.  During this process, some jury candidates clearly relish the opportunity to express their opinions while others make a concerted effort to be dropped from the squad; the majority just lay low and put their faith in the system.

In the end, I did not make the final cut though I had become increasingly enthused throughout the day.  While I had clues that the ax might fall, there is always a hint of pain when one is rejected, however reasoned that decision might be.  Those of us sent home were surely comforted by the knowledge that we had done our civic duty and, to be perfectly honest, were at least somewhat glad to leave behind the very serious responsibilities that come with selection.  But, for the most part, humans want to be chosen, acknowledged for our special traits, and, when rejected, we are prone to dwell on that lost opportunity (once again).

Saturday, January 12, 2013

Climbing through Time

Our journey from Columbia, Missouri, to Littleton, Colorado, climbs through geologic time.  In greater Columbia and along I-70 to its immediate west, outcrops of Mississippian limestone are evident, deposited in shallow seas some 320 million years ago (MYA).  By the time we reach western Missouri, we are riding atop Pennsylvanian sedimentary rocks, about 300 million years old; this strata continues into eastern Kansas.

West of Topeka and to the eastern outskirts of Junction City, I-70 undulates across the Flint Hills, where Permian sediments, including thin seams of coal, outcrop along road-cuts and stream valleys; these rocks were deposited about 220 MYA as Earth's Continents were merging into Pangea.  West of Junction City and throughout Central Kansas, the highway crosses Cretaceous limestones, shales and sandstones, deposited in and along a broad seaway that stretched from coastal Texas to southwest Canada when Tyrannosaurus rex roamed the planet, some 100 MYA.

Throughout the High Plains of western Kansas and eastern Colorado, Tertiary deposits lie atop the Cretaceous sea bed, eroded from the Front Range of the Rockies or blown in from pockets of volcanism throughout the American West.  This erosional debris, carried eastward by braided rivers, began to accumulate early in the Tertiary (60 MYA), following the initial rise of the Rockies, but increased dramatically during the Miocene-Pliocene Uplift (20-5 MYA) of the Colorado Plateau and Rocky Mountain corridor.  Finally, during the Pleistocene (2.5-0.01 MYA), wind-blown loess, from continental glaciers to the north and mountain glaciers to the west, coated some regions.  Along the South Platte and Arkansas Valleys, the Tertiary veneer has been removed, exposing the underlying Cretaceous sea deposits (primarily Pierre shale) upon which the rivers drop their own cargo of Quaternary sand and gravel.

Friday, January 11, 2013

A Walk on the MKT

Determined to enjoy this spring-like afternoon, I headed to the MKT for a walk.  This rail-to-trail greenbelt follows a series of stream valleys from downtown Columbia to the Missouri River floodplain where it joins the Katy Trail, a Missouri State Park.  Its 8.9 mile route, angling southwest from the city, crosses a pleasing mix of woodlands, meadows and wetlands, making the trail an excellent avenue for nature study.

Today, I was joined by the usual mix of fellow Columbians, dominated by the trail athletes, racing by on their fat-tire bikes or huffing along in their Nikes.  Family groups, dog walkers and cell phone addicts rounded out the crowd, all of whom were focused primarily on the trail itself.  I'm sure most of them relished the mild, humid air, tainted at times by Columbia's eco-friendly wastewater system, but I doubt few noticed the eastern bluebirds that fed along the meadows or the flock of cedar waxings that alighted in a trailside tree.  Neither did the outcrops of Mississippian limestone or gurgling streams draw their attention.

Then again, who am I to judge their priorities.  Many use our nature trails to exercise their bodies or to exorcise their demons.  Their focus is on their personal needs, not on the complexity of the natural surroundings.  While they enjoy her bounty in an abstract way, they know little about her history or her diversity.  After all, they think of themselves as visitors in her territory, not as creatures of her realm.  We naturalists take a different view.

Thursday, January 10, 2013

Winter Rain

Thanks to an upper level low, parked over Oklahoma, we have received a steady plume of Gulf moisture since early this morning, producing a gray overcast and intermittent showers.  The temperature in central Missouri has gradually climbed through the day and should peak near 50 degrees F.  As a potent cold front approaches from the northwest, the southerly flow will intensify and overnight lows may not dip below today's high; by tomorrow afternoon, we should be in the mid to upper sixties.

Chilly, winter rain is among the least pleasant of weather conditions but, in light of our prolonged drought, we'll take every drop that comes our way.  Unfortunately, the primary moisture plume is flowing east of our region and heavy rains will mainly douse the lower Mississippi and Ohio Valleys; potent thunderstorms are expected to remain along the Gulf Coast.  Nevertheless, we'll receive a welcome dose of spring in mid January before the next winter storm sweeps in from the Plains.

Meanwhile, the days are steadily lengthening, great horned owls are nesting and tree squirrels have become noticeably frisky as their mating season begins.  Our march toward spring has gained momentum, fueled by a higher sun and, to date, a decent amount of winter precipitation.  Hopefully, this winter rain is a sign that the La Nina cycle has run its course and that the parched American Heartland will enjoy a regular supply of rain and snow in the coming months.

Wednesday, January 9, 2013

The Nature of Viruses

Viruses are sub-cellular agents of infection that must utilize the cellular machinery of bacteria, plants or animals in order to reproduce.  Composed of a single strand of genetic material (DNA or RNA) encased in a protein capsid, a virus is too small to be seen by standard light microscopy; indeed, most are less than one hundredth the size of a bacterium.

Specific proteins on the viral capsid attach to receptors on the host cell; this attachment process is essential to viral infectivity and explains why viruses may only infect the cells of certain species or may only infect certain cells or tissues within a given host species.  While the infecting virus triggers an immune response in the host, some are capable of suppressing that response by infecting and killing cells that control immunity (e.g. HIV attacks lymphocytes).  In addition, while most infected cells are destroyed by viral replication, some viruses enter a latent phase within cells, reactivating in the future to produce chronic or relapsing infections.  Many viruses use specific carriers (known as vectors) such as mosquitoes, ticks, bats and rodents that transmit the virus to a susceptible host while others are spread between individuals via blood contact or through respiratory, intestinal or sexual secretions.  Of special concern is the fact that mutations within the viral genome may allow viruses to skip from one host (e.g. birds, swine, monkeys) to another (e.g. humans), unleashing pandemics.

Many common human infections are produced by viruses; these include the common cold, influenza, mononucleosis, herpes infections (including shingles), viral hepatitis (A, B, C and others), HIV, viral gastroenteritis, conjunctivitis, viral pneumonia, encephalitis, viral meningitis and viral infections of the heart, including pericarditis and myocarditis.  While viruses do not respond to antibiotics, specific antiviral agents may control (though not cure) chronic disease (such as HIV, Hepatitis B and Hepatitis C) or may modify the severity of acute infection (as in influenza and herpes infections).  However, in most viral infections, treatment is, for now, purely symptomatic and supportive.  On the other hand, vaccines are capable of preventing some viral infections (e.g. herpes simplex, measles, mumps, rubella, varicella, Hepatitis B) or reducing the severity of an acute infection (e.g. influenza).  Beyond the acute or chronic illness that they produce, some viral infections (such and Hepatitis C and certain strains of herpes simplex) are known to be precursors of malignancy.  Finally, many researchers suspect that viruses play a role in the pathogenesis of chronic illnesses such as multiple sclerosis and autoimmune disorders.

Update (2017) - Since this post was written, drugs have been developed that cure Hepatitis C; no doubt, other cures for viral infections will follow.  R. Folzenlogen

Tuesday, January 8, 2013

San Juan Volcanism

The San Juan Mountains of southwest Colorado overlie the remnants of Uncompahgria, the western uplift of the Ancestral Rocky Mountains that rose late in the Paleozoic Era, some 300 million years ago (MYA).  Throughout the Mesozoic Era, erosive forces decimated this range, spreading sediments across the region.  Then, during the Cretaceous Period (about 100 MYA), a seaway covered the area, adding marine and coastal deposits.  As the Cenozoic dawned, 65 MYA, the Laramide Orogeny was underway, folding the Northern and Central Rockies and buckling the crust of the San Juan region as well.

During the Oligocene, about 35 MYA, volcanism developed in southwest Colorado; this mountain building process continued for 5 million years and was followed by a phase of explosive eruptions that produced the massive calderas of the San Juans.  Finally, during the Miocene (25 MYA), a second phase of volcanism, basaltic in nature, developed across southern Colorado and northern New Mexico in concert with crustal stretching and the formation of the Rio Grande Rift; igneous plutons and laccoliths also rose with the Colorado Plateau during this Period and have since been uncovered by erosion.

The current topography of the San Juan region, which is bisected by a westward curve of the Continental Divide, is the product of Pleistocene mountain glaciers that sculpted the layered and folded strata described above.  Though less intense, the erosion continues today, conducted by the upper tributaries of the Rio Grande, Gunnison, Uncompahgre, Dolores, San Juan and Animas Rivers.

Monday, January 7, 2013

Earth's Ice Ages

Over the 4.6 billion year history of our planet, five major ice ages have occurred in addition to other periods of climate cooling.  The specific cause for these events is most likely multifactorial, including alterations in solar radiation (related to both solar output and subtle changes in the Earth's orbit), fluctuating ocean currents (primarily secondary to plate tectonics and continental drift) and chemical changes in the Earth's atmosphere as a consequence of vegetation patterns, volcanic activity, asteroid impacts and both the production and absorption of greenhouse gases (primarily methane and carbon dioxide).

The first major Ice Age, known as the Huronian, developed about 2.4 billion years ago, while the Cryogenian began 850 million years ago and may have nearly enveloped the entire planet in a sheet of ice; both of these early Ice Ages lasted more than 200 million years.  The Andean-Saharan Ice Age stretched from 460-420 million years ago (MYA) while the Karoo Ice Age began 360 MYA and lasted 100 million years.  The fifth major Ice Age, known as the Quaternary Glaciation, began about 2.5 MYA and, most climatologists believe, continues today (though we are currently in one of its warm interglacial periods that began 10-15,000 years ago).  Periods of climate cooling also occurred during the Oligocene, about 35 MYA and the Miocene, some 15 MYA, each lasting 10 million years or more; it was during the Oligocene cooling that the Antarctic ice sheet began to form, now harboring 60% of the freshwater on Earth.

It should be emphasized that Ice Ages are characterized by prolonged periods of climate cooling and glaciation (both continental and cordilleran) but are broken by relatively warm interglacial periods such as the one in which we live.  During these warm periods, glaciers retreat and sea levels rise; conversely, as the climate cools, glaciation expands, sea levels fall and continental land masses expand (including the formation of land bridges).  The current warming cycle is progressing at an exceptionally rapid rate and most climatologists are convinced that human activity (including fossil fuel utilization and deforestation) is responsible.  There is little doubt, however, that, within another 20,000 years or so, the climate will begin to cool and the ice will return.

Sunday, January 6, 2013

Mallard Invasion at Eagle Bluffs

Yesterday morning, under a gray overcast and scattered snow, I headed down to Eagle Bluffs Conservation Area, southwest of Columbia.  Never knowing what to expect on my frequent visits to that floodplain refuge, I didn't have to wait very long.  Just east of the entry road, a massive flock of mallards nearly filled an open field; restless, they had likely arrived overnight, escaping frozen wetlands to our north.

After observing them for a while, I entered the refuge.  While many of the ponds and channels were iced over, pockets of open water held small flocks of mallards, gadwalls, northern shovelers and green-winged teal.  A large flock of Canada geese fed on a snowy meadow while great blue herons moved between the open pools.  Red-tailed hawks and northern harriers patrolled the grasslands and a half dozen bald eagles perched in trees, no doubt watching for sick or injured waterfowl on which to feast.

As I left the refuge, perhaps an hour later, the migrant mallards were rising from the entrance field; circling in waves above their tired cohorts, they drew hundreds more into the air and, en masse, they moved south through the Missouri River Valley.  While veteran birders often dismiss common species such as mallards, the spectacle of massive flocks never fails to inspire even the most experienced naturalist and, speaking for myself, it was an awesome sight.

Saturday, January 5, 2013

Major Meteor Showers

As we hurtle through space on our annual journey around the sun, the Earth is constantly impacting debris from asteroids and comets.  Igniting from friction with our planet's atmosphere, they produce meteors (commonly known as shooting stars) that are visible every night of the year; in fact, some are bright enough to be seen during the day.  The displays peak as the Earth crosses the path of the parent bodies and there are more than 50 named meteor showers in the course of a year; this post lists the major events.

The Quadrantids peak on January 4 and may yield 60 meteors per hour while the March Geminids peak on March 22 and produce about 40 meteors per hour.  The Lyrids offer about 30 meteors per hour through the second half of April and the Eta Aquarids, remnants of Halley's Comet, peak from May 4-5.  The June Bootids (or June Draconids), produced by the Pons-Winnecke Comet, peak on June 30 but are highly erratic from year to year.  Delta Aquarids streak across the night sky on July 28-29 and the Alpha Capricornids peak on July 29-30.  The Perseids, recognized as the most reliable of our annual showers, are remnants of the Swift-Tuttle Comet and peak from August 10-12, yielding up to 100 meteors per hour.

The Draconids, left behind by the Glacobinni-Zinner Comet, peak from October 8-9 and may produce 200 or more meteors per hour.  The Orionids, debris from Halley's Comet, peak from October 20-21 while the Leonids from the Temple-Tuttle Comet peak on November 17 and may provide spectacular displays.  The Geminids, from the 3200 Phaeton Asteroid, peak from December 13-14 and the Ursids close out the year on December 22-23.  Meteor showers are best observed after midnight and away from city lights; of course, the moon phase also impacts viewing since moonlight will diminish the perceived brightness of the meteors.

Friday, January 4, 2013

The English Channel

Back in the Eocene, some 50 million years ago (MYA), as mammals exploded in number and variety,  the English Channel did not exist.  England and France were a continuous land mass and the current region of the Channel was underlaid by a layer cake of early Tertiary, Mesozoic and Paleozoic sediments (top to bottom) that sat atop the Precambrian basement.  Then, in the Oligocene (about 30 MYA), in concert with the Alpine Orogeny, the crust buckled, producing a broad ridge that stretched from southern England to northernmost France.

Known to geologists as the Weald-Artois anticline, the ridge is oriented ENE to ESE.  Erosion has uncovered the layered sediments that warp across the ridge; along the central axis (known today as the Weald), Jurassic and early Cretaceous sandstones and shales are exposed while, on the north and south flanks, late Cretaceous chalk forms escarpments that face inward.  Now known and the North and South Downs, the soft chalk has eroded into swaths of low hills and ridges that parallel the axis of the anticline.

During the final quarter of the Pleistocene (less than 500,000 years ago), at least two glacial floods scoured the region, opening the English Channel and its narrow Dover Strait, thereby connecting an arm of the Atlantic with the North Sea and separating England from the primary land mass of Europe.  Along the southeastern coast of England and the northern tip of France, cliffs of the late Cretaceous chalk now rise above the Channel, widely known as the White Cliffs of Dover.  Indeed, the Cretaceous Period was named for these beautiful cliffs and the other chalk outcrops of northern Europe (creta is Latin for chalk).

Thursday, January 3, 2013

Unexpected Raptors

On our recent trip to Ohio, following a monotonous, eight-hour drive across the flat Glaciated Plain, we turned north on I-71, angling toward the Appalachian Plateau.  To that point, my wildlife observations had been limited to starlings, pigeons, crows and those reliable red-tailed hawks; there were also quite a few white-tailed deer along the highway, almost all bloodied and lifeless on the side of the road.  Then, about ten miles north of Columbus, a peregrine falcon streaked across the Interstate, no doubt targeting a flock of waterfowl beyond trees to our west.

Then, yesterday afternoon, sunny, cold weather coaxed me into the countryside and I rescued my wife's Beetle from its winter hibernation.  Despite the invigorating weather and snowy landscape, my bird sightings were limited to a flock of waxwings and the occasional cardinal or mockingbird before I caught sight of a bulky form in a lone, barren tree.  Sure enough, the distinctive shape proved to be that of a barred owl, basking in the mid-day sun and likely watching for signs of voles beneath the snow.  Frequently active early and late in the day, especially in spring, barred owls are not often encountered on a bright winter afternoon and I certainly welcomed his presence.

Such are the rewards that feed the enthusiasm of naturalists.  Regardless of the weather, landscape or time of day, unexpected sightings can and do occur.  After all, if the events of every hike or road trip were known in advance, all sense of adventure would be lost.

Wednesday, January 2, 2013

Europe's Grand Canyon

Flowing northward through Montenegro, the Tara River has carved a spectacular canyon through the Mesozoic limestones and dolomites of the Dinaric Alps.  Fifty miles long and almost 4300 feet deep, the Tara River Canyon is the longest and deepest canyon in Europe and the second largest canyon on our planet (exceeded only by the Grand Canyon of the Colorado River in the American Southwest).

The Tara, a tertiary tributary of the Danube, is renowned for its clear, blue-green water and the steep walls of its canyon harbor an abundance of caves, springs and waterfalls, typical of karst topography.  The magnificent gorge, long protected by its depth and sheer rock cliffs, harbors large stands of ancient black pine (some more than 400 years old), mixed with a rich deciduous forest of ash, birch and beech. Native flora and fauna include over 700 plant species and wildlife such as gray wolves, brown bears, wild boars, chamois, Balkan lynx, golden eagles and river otters.

Threatened repeatedly by plans to build a hydroelectric plant in the gorge, the Tara River Canyon is, for now, protected within Durmitor National Park and has been designated a UNESCO World Heritage Site. Access to the gorge remains limited but ecotourism, including raft and kayak trips on the turbulent river could, unless carefully monitored, have a negative impact on this pristine wilderness.

Tuesday, January 1, 2013

The Keys to Longevity

On New Years Day, we pause to remember those who died over the past year and then look to the future, making resolutions that, we believe, will enhance our health, happiness and success.  Those of us who are middle-aged or older are apt to focus primarily on our mortality, placing emphasis on choices that might extend our time on this planet.  In the end, our longevity is determined by three factors: our genes, our lifestyle choices and our luck.

Since we cannot choose our parents, our genetic traits are beyond our control but play a major role in the lifespan that we might anticipate; having parents who lived long, healthy lives portends a relatively high incidence of longevity.  On the other hand, recessive traits, inherited from both parents, might put us at risk for certain diseases that neither of them faced.  Fortunately, modern medicine offers therapy for an increasing number of genetic disorders, blocking the expression of pathologic genes or supplementing essential proteins, enzymes or cofactors that, due to defective genes, we are unable to produce.

For those fortunate to have inherited a good set of genes, longevity will be determined primarily by their lifestyle choices and their luck.  Those who consume nutritious, well balanced meals, avoid excessive alcohol, abstain from the use of tobacco and illicit drugs, adhere to a regular schedule of aerobic exercise, monitor and treat risk factors such as hypertension and hyperlipidemia, wear seatbelts and avoid risky behavior, have a much better chance of living a long, healthy life than those who ignore these recommendations.  Finally, our longevity also depends on luck, the good fortune to have avoided death due to accidents, murder, natural disasters and other events beyond our control.  Unfortunately, the knowledge that life is fickle and that death is often random instills a degree of fatalism in many humans, diminishing their commitment to the healthy lifestyle choices enumerated above.