Along the Pacific Coast, from southern British Columbia to northern California, three small tectonic plates lie between the Pacific and North American Plates. The Juan de Fuca Plate is the largest, stretching from the center of Vancouver Island to the southern border of Oregon, while the Explorer Plate sits north of it and the Gorda Plate lies off northern California; all three, like the Cocos Plate off Central America and the Nazca Plate along the west coast of South America, are remnants of the oceanic Farallon Plate, most of which has since subducted beneath the North and South American Plates.
On the west side of the three plates, they are spreading from the Pacific Plate along a broken oceanic ridge while, on their east side, they are subducting beneath the North American Plate. Between the spreading zones, each plate also has a transform-fault margin with the Pacific Plate, where the plates are scraping against one another; in addition, horizontal (east-west) faults form the boundaries between the Juan de Fuca Plate and its smaller neighbors. In this complex tectonic region, earthquakes may thus be generated at the subduction zones, along the transform faults or at the faults that separate the three plates.
Yesterday's 6.4 magnitude quake occured off the west coast of Vancouver Island, along the subduction zone and very near the margin between the Explorer and Juan de Fuca Plates. Rather shallow (14 miles deep), it was felt as far away as northern Washington but, fortunately, did not produce significant damage. Of course, there is always the potential for strong quakes in this region and those that occur along the subduction zone could produce a catastrophic tsunami. Hopefully, regularly occuring weak quakes might diminish the risk for such an event.
Sabtu, 10 September 2011
Jumat, 09 September 2011
The Energy of Autumn
Rescued from the intense sun and oppressive heat of summer, we humans and our wild neighbors become more active as autumn envelops the Heartland. Birdsong, while not as feverish as the chorus of spring, reignites on these cool mornings and the call of the barred owl echoes through the woodlands. Sensing the approach of winter, hoarders of all variety are active throughout the day, stocking their dens with seeds, nuts and hay.
Many songbirds are noticeably restless, preparing to depart for wintering grounds, while our permanent residents gather in large, seasonal flocks, roaming about the fields and wetlands. Large herbivores, storing energy for the trials of winter, are also stirred by hormones as their annual rut begins. Taking advantage of their active prey, our native predators, avian, reptilian and mammalian, hunt throughout the day and night, culling the weak and ensuring their own survival as the autumn chill intensifies.
We humans, ingrained with the collective memories of our ancestors, are also energized by this seasonal change. Awakened from our summer stupor, we relish outdoor adventures, stretching our muscles and soothing our minds amidst the colorful autumn landscape. Of course, we also sense the coming threat of winter, harvesting our crops, filling our pantries and, for some, taking part in the seasonal hunts that typify our culture. Like our wild neighbors, we know that the invigorating days of fall will soon yield to a dark, frigid season that, for humans, is uncomfortably foreign to our tropical nature.
Many songbirds are noticeably restless, preparing to depart for wintering grounds, while our permanent residents gather in large, seasonal flocks, roaming about the fields and wetlands. Large herbivores, storing energy for the trials of winter, are also stirred by hormones as their annual rut begins. Taking advantage of their active prey, our native predators, avian, reptilian and mammalian, hunt throughout the day and night, culling the weak and ensuring their own survival as the autumn chill intensifies.
We humans, ingrained with the collective memories of our ancestors, are also energized by this seasonal change. Awakened from our summer stupor, we relish outdoor adventures, stretching our muscles and soothing our minds amidst the colorful autumn landscape. Of course, we also sense the coming threat of winter, harvesting our crops, filling our pantries and, for some, taking part in the seasonal hunts that typify our culture. Like our wild neighbors, we know that the invigorating days of fall will soon yield to a dark, frigid season that, for humans, is uncomfortably foreign to our tropical nature.
Kamis, 08 September 2011
A Miocene Supernova
The Miocene Epoch of the Tertiary Period stretched from 22 million years ago (MYA) to 5 MYA. During that time, ancestral apes and early hominids appeared in Africa, Kure Island (now an atoll) and Midway Island developed above the Hawaiian hotspot, the Columbia Plateau formed from massive basalt flows, Iceland emerged from the sea, the Intermountain West was uplifted another 5000 feet, the Gulf of Aden began to open and the East African Rift started to form. In addition to ancestral apes and hominids, the first true elephants, giraffes, okapis, hippos and North American pronghorns made their appearance.
Two weeks ago, on August 24, astronomers from the University of California observed the sudden appearance of a supernova in the Pinwheel Galaxy, 21 million light years from Earth; in other words, they observed the explosion of a star that occured during the early Miocene. Brightening by the day, the display is expected to peak between September 9 and September 12, when it should be visible with powerful binoculars or a small telescope. Located in the Ursa Major (Big Dipper) constellation, the supernova will appear as a bluish-white star just above and slightly left of the last two stars in the Big Dipper's handle.
When we look at the night sky, we are looking back in time. The light from stars, traveling at 186,000 miles per second, takes years to reach Earth, even from our closest neighbors; Sirius, for example, the brightest star in the sky, is 8.7 light years away (if it exploded eight years ago, we will not know until next May). While the Miocene supernova in the Pinwheel Galaxy exploded 21 million light years from Earth, it was a nearby event relative to the vast expanse of the Universe.
Two weeks ago, on August 24, astronomers from the University of California observed the sudden appearance of a supernova in the Pinwheel Galaxy, 21 million light years from Earth; in other words, they observed the explosion of a star that occured during the early Miocene. Brightening by the day, the display is expected to peak between September 9 and September 12, when it should be visible with powerful binoculars or a small telescope. Located in the Ursa Major (Big Dipper) constellation, the supernova will appear as a bluish-white star just above and slightly left of the last two stars in the Big Dipper's handle.
When we look at the night sky, we are looking back in time. The light from stars, traveling at 186,000 miles per second, takes years to reach Earth, even from our closest neighbors; Sirius, for example, the brightest star in the sky, is 8.7 light years away (if it exploded eight years ago, we will not know until next May). While the Miocene supernova in the Pinwheel Galaxy exploded 21 million light years from Earth, it was a nearby event relative to the vast expanse of the Universe.
Rabu, 07 September 2011
Common Mullein
Driving through the American countryside, especially across semi-arid grasslands of the West, one readily concludes that common mullein is native to North America. Yet, this widespread plant, easily recognized by its tall, flowering stalk, is native to Eurasia and North Africa; it was introduced to America by European colonists in the early 1700s and was initially culivated for medicinal purposes.
Favoring abundant sunshine and well-drained soil, common mullein is a biennial, requiring two years to complete its life cycle. Following germination, the plant forms a rosette of large, velvety leaves which persists through the following winter; as the second spring progresses, a tall stalk is produced (often rising 6 feet or more) on which numerous, compact, yellow flowers develop. These flowers, which bloom in sequence from late June through mid September, are pollinated by bees, other insects or wind currents; an abundant crop of tiny seeds, eaten by goldfinches and buntings, remain on the drying stalk through the winter and are eventually scattered by the wind. Able to survive long periods of dormancy, mullein seeds are programmed to await ideal growing conditions and may not germinate for decades.
Like other prolific aliens, such as dandelions and starlings, common mullein owes its success in North America to the human tendency to manipulate natural ecosystems. Once introduced into a new environment, the reproductive potential of alien species is often impossible to contain and, to the chagrin of gardeners, farmers and ranchers, they become naturalized "weeds or pests". Since common mullein is clearly here to stay, we might as well enjoy the seasonal beauty of these tall, sun-loving plants.
Favoring abundant sunshine and well-drained soil, common mullein is a biennial, requiring two years to complete its life cycle. Following germination, the plant forms a rosette of large, velvety leaves which persists through the following winter; as the second spring progresses, a tall stalk is produced (often rising 6 feet or more) on which numerous, compact, yellow flowers develop. These flowers, which bloom in sequence from late June through mid September, are pollinated by bees, other insects or wind currents; an abundant crop of tiny seeds, eaten by goldfinches and buntings, remain on the drying stalk through the winter and are eventually scattered by the wind. Able to survive long periods of dormancy, mullein seeds are programmed to await ideal growing conditions and may not germinate for decades.
Like other prolific aliens, such as dandelions and starlings, common mullein owes its success in North America to the human tendency to manipulate natural ecosystems. Once introduced into a new environment, the reproductive potential of alien species is often impossible to contain and, to the chagrin of gardeners, farmers and ranchers, they become naturalized "weeds or pests". Since common mullein is clearly here to stay, we might as well enjoy the seasonal beauty of these tall, sun-loving plants.
Senin, 05 September 2011
Weather and the Seasons
We humans define the seasons by the solar cycle or by our own, somewhat arbitrary calendar. According to the first, more natural definition, the seasons stretch between the solstices and the equinoxes while, on the latter, each is assigned a three month block, based on cultural and religious tradition.
It is, of course, the tilt of Earth's axis that produces our seasonal change, as the angle of sunlight (and subsequent surface heating) varies through the year. While there is limited annual solar variation in the Tropics, there is a dramatic seasonal change at the poles, with periods of perpetual light and darkness; between these extremes, the seasonal variance correlates with latitude but may also be affected by ocean currents or the proximity to large bodies of water, which moderate conditions on the adjacent land.
Nevertheless, as we all know, seasonal weather expectations, based on long term observations, are not always met. Stagnant weather patterns or sudden shifts in the jet stream can produce a spring without rain, a chilly summer or a week of balmy days in the midst of winter. While our wild neighbors respond primarily to the light cycle and readily adapt to changing conditions, we humans are prone to emotional turmoil when the weather and seasons are out of sync. Unfortunately, nature is oblivious to human expectations and we must accept (if not cherish) her whimsical temperament.
It is, of course, the tilt of Earth's axis that produces our seasonal change, as the angle of sunlight (and subsequent surface heating) varies through the year. While there is limited annual solar variation in the Tropics, there is a dramatic seasonal change at the poles, with periods of perpetual light and darkness; between these extremes, the seasonal variance correlates with latitude but may also be affected by ocean currents or the proximity to large bodies of water, which moderate conditions on the adjacent land.
Nevertheless, as we all know, seasonal weather expectations, based on long term observations, are not always met. Stagnant weather patterns or sudden shifts in the jet stream can produce a spring without rain, a chilly summer or a week of balmy days in the midst of winter. While our wild neighbors respond primarily to the light cycle and readily adapt to changing conditions, we humans are prone to emotional turmoil when the weather and seasons are out of sync. Unfortunately, nature is oblivious to human expectations and we must accept (if not cherish) her whimsical temperament.
Sabtu, 03 September 2011
Front Range Upslope
As I packed my truck yesterday morning, it was sunny and mild in Littleton, Colorado. However, I noticed a swath of low clouds across the eastern horizon and the Front Range foothills had taken on a hazy appearance. Before I left the city, heading east, the gray clouds had spread westward, shrouding most of Metro Denver, and the temperature dropped in concert. East of the city, near Byers, I encountered mist and dense fog, which enveloped the highway until I crossed the Palmer Divide; beyond that topographic barrier, as the air was forced to decend, the fog disappeared and breaks appeared in the gray overcast.
The above account is typical of an upslope weather event, which occurs along the Front Range in the wake of a cold front; while the Continental Divide blocks the first band of clouds and precipitation as the front moves from west to east, northeast winds develop behind the front, pushing cool air and moisture toward Denver from the northern High Plains. As the air is forced to rise across increasingly higher terrain, low clouds form and precipitation develops; depending on both the availability of moisture over the Plains and the temperature of the air, this precipitation may be light or heavy and may fall as rain or snow. Once the front moves further east and the upslope flow resolves, the clouds and precipiation dissipate.
Yesterday's system was relatively starved of moisture and precipitation was minimal. I finally caught up with the front itself in western Kansas; while Goodland was raked with chilly, north winds under cloudy skies, Colby, just 30 miles to the east (but still ahead of the front) was sunny and warm, with strong, southwesterly winds. Though many regions of our country claim to experience rapidly changing weather, few compare to the Mountain West, where the varied topography has a dramatic effect on weather systems and where wind direction is often the primary factor when it comes to temperature and precipitation.
The above account is typical of an upslope weather event, which occurs along the Front Range in the wake of a cold front; while the Continental Divide blocks the first band of clouds and precipitation as the front moves from west to east, northeast winds develop behind the front, pushing cool air and moisture toward Denver from the northern High Plains. As the air is forced to rise across increasingly higher terrain, low clouds form and precipitation develops; depending on both the availability of moisture over the Plains and the temperature of the air, this precipitation may be light or heavy and may fall as rain or snow. Once the front moves further east and the upslope flow resolves, the clouds and precipiation dissipate.
Yesterday's system was relatively starved of moisture and precipitation was minimal. I finally caught up with the front itself in western Kansas; while Goodland was raked with chilly, north winds under cloudy skies, Colby, just 30 miles to the east (but still ahead of the front) was sunny and warm, with strong, southwesterly winds. Though many regions of our country claim to experience rapidly changing weather, few compare to the Mountain West, where the varied topography has a dramatic effect on weather systems and where wind direction is often the primary factor when it comes to temperature and precipitation.
Kamis, 01 September 2011
Sharptail Ridge
South of Metro Denver, the terrain gradually rises toward the Palmer Divide and has been sculpted into a maze of ridges and mesas by the tributaries of the South Platte River. Douglas County has set aside one of these ridges as an open space preserve, chosen to protect breeding habitat for sharp-tailed grouse. A parking area off Roxborough Park Road is the access point for a 4.4 mile trail that winds up and along the ridge, eventually intersecting a network of trails in the foothills. From the trailhead, which sits at an elevation of 5800 feet, the trail winds southward and gradually upward, crossing shortgrass prairie studded with yuccas, prickly pear cacti and a wide variety of wildflowers. Grassland sparrows, Say's phoebes, meadowlarks, sharp-tailed grouse and open country raptors, such as kestrels, prairie falcons and golden eagles, are often observed along the way and signs warn visitors to watch for prairie rattlesnakes that may sun themselves on the trail.
As the trail climbs higher, changing views of the nearby foothills, distant mountains and Metro Denver unfold to the west and north. Two miles from the trailhead, near an elevation of 6000 feet, the path reaches a swath of foothill shrublands which blanket the more shaded slopes of the ridge. Here you may find rufous-sided and green-tailed towhees, lesser goldfinches, blue-gray gnatcatchers, black-headed grosbeaks, scrub jays and other avian residents of the lower Transition Zone. Just past this area the trail reaches the crest of the ridge and views extend to other ridges and mesas of the Plum Creek watershed; unfortunately, one also observes that residential developments are spreading westward, toward the foothills, placing emphasis on the importance of Sharptail Ridge and other open space preserves.
Those who plan to visit this scenic refuge are advised that dogs and trail bikes are not permitted. In addition, the preserve is closed to the public during most weeks from mid September to late November, when licensed deer and elk hunting occur in the area. Indeed, elk herds winter along this ridge and may attract mountain lions from the adjacent foothills; other predators include coyotes, red fox and raptors, as mentioned above.
As the trail climbs higher, changing views of the nearby foothills, distant mountains and Metro Denver unfold to the west and north. Two miles from the trailhead, near an elevation of 6000 feet, the path reaches a swath of foothill shrublands which blanket the more shaded slopes of the ridge. Here you may find rufous-sided and green-tailed towhees, lesser goldfinches, blue-gray gnatcatchers, black-headed grosbeaks, scrub jays and other avian residents of the lower Transition Zone. Just past this area the trail reaches the crest of the ridge and views extend to other ridges and mesas of the Plum Creek watershed; unfortunately, one also observes that residential developments are spreading westward, toward the foothills, placing emphasis on the importance of Sharptail Ridge and other open space preserves.
Those who plan to visit this scenic refuge are advised that dogs and trail bikes are not permitted. In addition, the preserve is closed to the public during most weeks from mid September to late November, when licensed deer and elk hunting occur in the area. Indeed, elk herds winter along this ridge and may attract mountain lions from the adjacent foothills; other predators include coyotes, red fox and raptors, as mentioned above.
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