Watching Al Jazeera

Like most Americans, I first became aware of Al Jazeera during the months following the September 11 terrorist attacks.  Based on reports from U.S. news organizations, it had the image of an underground network of jihadist sympathizers, known for their access to messages and videos from Osama Bin Laden. Never giving it much attention, I stumbled across an Al Jazeera broadcast several weeks ago while looking for something of value amidst the carnage of American cable channels.

To my surprise, it was a very sophisticated program, moderated from a massive, modern studio in Qatar; indeed, this Arab news organization was launched by the Emir of Qatar in 1996 and is still heavily funded by that government.  Watching for an hour or so, I viewed field reports from across the globe, including a few from the U.S.; rather than hearing the expected, negative rhetoric about America, I watched a report on our severe drought among other issues of concern to the average American.  While there was some coverage of our presidential race and of the ongoing conflicts in Syria and Afghanistan, these issues were placed in a broader, international context.  Throughout the program, I did not discern any hint of anti-American bias in the reports and it was refreshing to view our country and its policies from a distant and less encumbered perspective.

I am proud to be an American and relish the freedoms that we enjoy.  Nevertheless, despite our international generosity and our propensity for military intervention, we tend to be a self-absorbed nation.  Most Americans have little interest in foreign countries and know very little about their culture (let alone their location on a map).  Any hope for developing a cooperative spirit across this planet will hinge on our willingness to understand one another's point of view and the opportunity to watch news reports and discussions from other countries seems to be a good first step.

A Message from Birds

Birdwatchers take up their hobby for a variety of reasons.  First and foremost, birds are colorful and interesting creatures that are represented by a wide variety of species.  Furthermore, in most regions of our globe, their population changes with each season, composed of local residents, migrants and rare vagrants.  This keeps us interested throughout the year and birdwatching appeases the hunting instinct that, to some degree, is found in all humans.

In addition, since bird populations vary from one ecological region to another, the hobby of finding and listing the varied species is a good excuse for travel and adventure, taking us to local nature preserves, State Parks, National Wildlife Refuges and, for some birders, to unique birdwatching sites across the globe.  Finally, the study of birds leads to a broader knowledge of their habitats, including the plants in which they nest and feed and the other wildlife species that share their environment.  In the end, we come to better understand the diversity and complexity of nature itself.

Hopefully, most birders eventually recognize the unique lesson that birds have to offer.  More than any other group of creatures, birds tend to occupy different habitats in the course of a year; some migrate long distances, others meander about during the lean winter months and others, while remaining in the same general region, shift their favored habitat, diet and behavior as one season gives way to another.  Their welfare is thus dependent upon the health of varied habitats, whether clustered in one area or spread from one pole to another, highlighting the interdependence of ecosystems across our planet.  The more we accept that message, the more committed we become to the protection of all natural ecosystems, however distant they might be; in turn, the welfare of all creatures, including humans, is enhanced.

The Conservation Business

I assume that readers of this blog share my passion for habitat protection and wildlife conservation and, therefore, regularly donate to organizations that promote those causes.  However, I also assume that many of you, like myself, are dismayed by the weekly mailings and unwanted "gifts" that arrive from many of those organizations.  At times, I feel that the majority of my donations are consumed by this relentless solicitation and that, in fact, I am supporting an army of communication specialists rather than the conservation efforts that I hope to foster.

Of course, the organizations will cite the importance of their recruitment programs and likely have data to demonstrate the effectiveness of their mail campaigns.  Nevertheless, one wonders how conservation groups, mindful of deforestation and global warming, are so unconcerned about the tons of paper that they produce and the carbon footprint of their advertising and solicitation divisions.  A quarterly email would be far more appropriate.

For many of us, there is also an undercurrent of concern that many conservation organizations are, at heart, just money-making businesses, mimicking the deceptive nature of commercialized religions and some relief organizations.  Aware of the large and often affluent population of conservation-minded citizens, they may be primarily devoted to income generation (though they are, as an organization, officially nonprofit).  Perhaps my concerns are unwarranted but I have stopped supporting groups that respond to my check with a deluge of mail and thank you gifts.

A Dry Wetland

On our first visit to the Forum Nature Area in two months, we found that our local wetland preserve is completely dry.  Thanks to the prolonged heat and drought, the seasonal lake is now a broad grassland and the hillside woodlands have taken on the yellow-brown foliage of a color-starved autumn.

Since the floodplain soil receives moisture from those uplands, the purple and gold wildflowers of late summer adorn the fields, including goldenrods, blazing star and thistles.  Cardinals, American goldfinches, yellow warblers and indigo buntings also offer their color to the parched landscape but the frog chorus has been stifled as resident amphibians and aquatic turtles have been forced into their winter retreats far too early.

Hopefully, late summer and early autumn rains will recharge the streams and rejuvenate the marsh.  For now, herons, rails and egrets have escaped to the Missouri River floodplain, summer ducks and geese  have flown off to deeper lakes and migrant shorebirds will have to look elsewhere for their nutritious mudflats.  Except for the stagnant pools along Hinkson Creek, water cannot be found at the Forum wetland.

Castle Rock Escarpment

From Quinter, Kansas, Castle Rock Road leads southward, toward the Smoky Hill River Valley.  Yesterday afternoon, I followed that even, dirt-gravel road as it undulates across the High Plains, now a mosaic of parched grasslands and dry stream beds.  Swainson's hawks perched on the phone poles, prairie falcons cavorted above the yucca-studded hillsides and a lean, juvenile coyote loped across the road as my pickup and its dust cloud approached.  About 5 miles south of Quinter, outcrops of Cretaceous sea deposits appeared along the creek valleys and, at 10 miles, the route to Castle Rock cuts to the east on a narrower but equally even road.  Another 4 miles brought me to the preserve entrance, which is on private land; after crossing a cattle guard, one can take a loop road past the Castle and its adjacent, spectacular escarpment (be aware that this road is deeply rutted and uneven, requiring a four-wheel drive vehicle with high clearance).

The Castle, composed primarily of Cretaceous chalk, sits out from the escarpment, an erosional remnant as the valley has gradually widened; three of its pinnacles remain (though leaning precariously) while a fourth crumbled back in 2001.  While the Castle is an interesting and solitary geologic feature, the escarpment, to its south-southwest, is spectacular, with sculpted cliffs and badlands of Cretaceous chalk, limestone, shale and sandstone.  Amidst the broad, High Plains of Central Kansas, it seems to be out of place, better consigned to the colorful canyonlands of the Colorado Plateau.

This Cretaceous wonderland reminds us that some (if not most) of America's spectacular scenery cannot be viewed from our major highways and scenic byways; one must be willing to take graveled backroads and foot-trails to enjoy such gems.  Were Castle Rock and its Escarpment located in a smaller, eastern State, it would surely be a State Park, complete with paved roads, manicured trails, comfort facilities and an Interpretive Center.  While such development, to paraphrase Edward Abbey, might draw crowds of gawking tourists, it would also help to insure protection of the site and further the education of those who visit.  Then again, I enjoyed my visit in quiet solitude, broken only by the sound of the prairie wind.

Sea Floor Spreading

Sea floor spreading is the engine of Continental Drift, the heat-driven process that causes the geography of Earth's surface to undergo constant change.  This spreading occurs along a network of mid-oceanic ridges that lace the globe; separating tectonic plates, they do not necessarily run down the middle of our geographic oceans.  As the oceans open, the diverging plates cause other tectonic plates to collide, subduct or scrape along one another, lifting mountain ranges, igniting volcanoes and triggering earthquakes.

Spreading rates along these plate boundaries vary.  Divergence along the Mid-Atlantic Ridge, which does follow the general midline of that ocean, is among the slowest on Earth, averaging 2-3 cm per year, while that along the East Pacific Rise, which cuts across the southeastern quadrant of the Pacific Ocean, is 5 times that rate; indeed, the divergence between the Pacific and Nazca Plates, off the west coast of South America, is currently the most rapid sea floor spreading on our planet, exceeding 17 cm per year.  At the other extreme, there is no current spreading at some oceanic crust boundaries, such as that between the South American and Antarctic Plates.  Continent rift zones, such as the Rio Grande Rift of the American Southwest and the East African Rift are young spreading zones that, if not aborted, will eventually become mid oceanic ridges.

Ocean crust forms at these diverging plate boundaries and is recycled into the mantle along subduction zones, where it dips below more buoyant continental crust or another segment of oceanic crust.  Based on the rate of spreading and the maximum distance between a mid oceanic ridge and its corresponding subduction zones, oceanic crust has a current maximum age of 200 million years; in other words, the oldest oceanic crust on planet Earth, about to subduct in the northwest Pacific, formed near the end of the Triassic Period, when dinosaurs ruled the land.  Continental crust, on the other hand, while constantly changing its shape due to the combined effects of faulting, rifting and accretion, is very old, having initially formed at least 4 billion years ago; of course, most surface rock formations, deposited and molded atop the ancient Precambrian basement, are much younger, dating from 600 million years ago to recent volcanic, stream and glacial deposits.

Evolution on Mars

Now that Curiosity has safely landed on the surface of Mars, its future discoveries are greatly anticipated though, it seems to me, fairly predictable.  We already know a good deal about the Red Planet, including topographic evidence of past volcanism and stream erosion.  While specific details will unfold over the coming years, it is reasonable to assume that the evolution of Mars mirrored that of Earth during the first billion years of its history.

There is little reason to doubt that the same inorganic elements are found on both planets (though their relative abundance may vary) and that the early, tumultuous histories of Mars and Earth were very similar, including widespread volcanism and a gradual cooling of the planets' surfaces.  Despite its greater distance from the sun, Mars likely developed an Earth-like atmosphere while radiative heating and greenhouse gases offered temporary protection from the deadly chill of space.  Oceans formed as water accumulated in the geologic basins and surface streams, fed by rain, ice and snow, molded the volcanic ranges and carved stark canyons across the Martian plains and plateaus.  Assuming such conditions persisted for a billion years or so, unicellular life may have evolved in the oceans and might still exist in sub-surface aquifers.

By the time that more complex marine organisms were appearing on Earth, the surface conditions on Mars were deteriorating and the process of evolution had ground to a halt; the heat transfer mechanisms that produced continental drift and a protective atmosphere on Earth could not be sustained on a smaller planet so distant from the sun. There is little reason to believe that multicellular plants and animals ever appeared on Mars and essentially no chance that they ever colonized Martian land.  Nevertheless, many scientists suspect that Curiosity will find evidence of past unicellular marine life and that, some day, we might discover living microscopic organisms beneath the cold, desolate landscape of the Red Planet.

To Bury a Fox

Heading out to work on our Colorado farm this morning, I found a dead fox in the side yard.  It was the juvenile male that took up residence on the farm this spring.  Over the past two weeks, I have watched him trot along with a vole in his mouth, munch on our crop of apples and sniff his way across the pastures in search of other quarry.

On initial inspection, there was no apparent injury; I imagined he may have consumed something poisonous since he has had the habit of bringing baseballs, chew bones and other items in from neighboring properties.  Then, when I turned him over, I found a bloody gash across his chest, no doubt the handiwork of a coyote or older male fox.  If our farm was larger, I might have left him where he lie, a natural victim of nature's cycle.  I had no intention of calling the county wildlife patrol and have him end up in a landfill; neither could I leave him in place since the odor of decay would certainly annoy the locals.  So, despite the dry, hard-packed earth, I managed to bury him near a fence line, throwing on a layer of mulch for good measure.

It's always sad to come across dead animals, especially the young that have just begun to explore their home environment.  We accept the fact that nature is a balance of life and death but, given our own fears and our instinct for self-preservation, one is prone to mourn their fate.  Those of us who feel a kinship with wild creatures also want their death to be honored, not with ritual and mysticism, but by returning their body to nature's recyclers.

A Hummingbird Shower

Birdwatchers use a variety of means to attract hummingbirds; they are, after all, among our most attractive and fascinating birds.  Some of us use traditional feeders, filled with sweet, homemade nectar, while others plant a variety of flowering plants, such as trumpet vine, that hummingbirds visit.  Of course, a source of clean, fresh water is also effective, as with all birds.

Yesterday evening, while watering a row of chokecherries and lilacs, I discovered the most effective means of attracting hummingbirds that I had yet to experience.  Within a few minutes of spraying the shrubs with my patented thumb-pressure method, broad-tailed hummingbirds began to arrive from all directions, dipping through the mist or perching near the edge of the spray to cleanse their feathers.  At least ten individuals took advantage of the shower though only a few were bold enough to receive a thorough soaking; the latter group, relishing the downpour, were oblivious to my presence, offering a very close view of their attractive plumage.

This shower method of drawing in hummingbirds was surely augmented by our recent hot weather and dearth of rainfall.  It was easy to empathize with the joy of their discovery and I was hesitant to move on until their enthusiasm waned.  Like the hummingbirds and the plants, I thoroughly enjoyed the experience.

Year of the Crabapple

Despite the heat and drought, this has been a good year for fruit production on our Littleton, Colorado, farm.  A mild spring, devoid of a late hard freeze, has led to large crops of apples, pears, chokecherries, wild cherries, Oregon grapes and mulberries; we've even had a fair number of apricots and peaches, an unusual occurrence since those trees bloom early, during the fickle weather of March.  But this year's productivity award goes to the crabapple trees, especially a large one next to our garage.

Loaded with more fruit than I have ever seen in an individual tree, the crabapple has started to drop its cargo early this year, likely in response to the hot, dry weather.  The small, hard, sour apples litter our backyard and every small breeze produces another windfall, drumming against the garage roof and pelting the ground like hail.  Yet, an abundant supply remains within the tree, glowing amidst the green leaves during the day and regularly thudding to earth overnight, often awaking us from sleep.

A fastidious lawn master may be disgruntled by this crabapple bonanza but we let the farm naturalize as much as possible.  Mule deer wander in to munch on the fruit and raccoons, skunks and mice surely raid the fallen apples at night; even our resident fox joins in the feast.  While some birds such as jays, magpies and waxwings may eat crabapples, most songbirds are attracted to the insects that invade the fruit or to the nectar that those blighted apples liberate.  Despite their firm, tart pulp, crabapples have long been harvested by humans as well, who use them to produce chutney, jellies, sauces or juice; like other apples, they are nutritious, rich in fiber and antioxidants.

Basalt: Rock of the Ages

As the primordial Earth began to cool, almost 4.6 billion years ago, the magma across its surface was subjected to the planet's gravity and lighter elements and minerals moved upward, forming a layer of inorganic material that would eventually coalesce to cover 30% of the globe.  The other 70% would cool to form basalt, a more dense, fine grained rock, rich in silica, ferro-magnesium minerals and, in some regions, olivine.  The lighter elements formed the continental crust while basalt formed the oceanic crust; as heat currents evolved in the underlying mantle, the crust broke into tectonic plates, some of which were comprised of both continental and oceanic crustal segments.

Throughout the history of our planet and continuing today, basalt forms from magma along the mid-oceanic ridges and moves outward as oceanic crust on the diverging plates.  Should the oceanic plates move over a hotspot, produced by a mantle plume, basalt volcanic islands are produced; the Hawaiian Chain provides the classic example of hotspot basalt islands while Iceland has formed from basalt volcanism above the mid Atlantic ridge.  At subduction zones, where an oceanic plate is forced down toward the mantle by an overriding continental or oceanic plate, the basalt melts and returns to the surface via subduction volcanoes, mixing with andesite if the upper plate is continental crust.  Basalt also rises to the surface at rift zones, where continental crust is pulling apart; this can occur in the form of volcanoes or surface flows.  Among the latter were the massive flows of the Siberian Traps (late in the Permian Period), the Deccan Traps of India (late in the Cretaceous Period) and the Columbia River Plateau of the Pacific Northwest (late in the Tertiary Period).  Smaller areas of basalt volcanism continue today in the Rio Grande and East African Rift Valleys, among other locations; such rifting activity may abort or may eventually produce a new seaway and thence a new ocean (as the rift zone converts to a mid oceanic ridge).

Having played a major role in the formation of Earth's crust and in the ongoing process of continental drift, basalt is truly a rock of the ages.  Needless to say, it is the most abundant and widespread rock on the surface of our planet (though most remains hidden beneath the ocean waters).

The Nature of Rocks & Minerals

Rocks, whether pebble or mountain sized, are composed of one or more minerals. Minerals are naturally occurring elements or chemical compounds with a unique crystalline structure; among these compounds are various sulfates, sulfides, halides, carbonates, nitrates, oxides, hydroxides, phosphates, silicates and others.  It is the chemical structure of a mineral that determines its physical characteristics, such as hardness, transparency, friability, color, luster, specific gravity, radioactivity and fluorescence.  To date, more than 3000 minerals have been identified on Earth; common examples include quartz, talc, dolomite, copper, gold, rock salt and hematite.

Rocks are broadly classified as igneous (having formed from magma), sedimentary (having formed from debris that settled in topographic basins, along stream channels or at the bottom of lakes and oceans) or metamorphic (igneous or sedimentary rocks that have been transformed by heat and pressure).  Granite is the classic example of igneous rock, sandstones, shales and limestones are common sedimentary rocks and both marble and slate are well-known metamorphic rocks.  Igneous rocks are sub-classified as intrusive (having cooled beneath the surface), extrusive (having cooled above the surface) or hypabyssal (having cooled within fractures or between layers of the continental crust); laccoliths, plutons and batholiths are examples of intrusive rock formations, basalt flows (the Deccan Traps, the Columbia Plateau) provide a classic example of extrusive rock strata while pegmatites, amalgams of various minerals and rocks, offer an example of hypabyssal formations.

Of course, this outline is deceivingly simple.  Even minor changes in the mineral content of rocks can dramatically alter their appearance and other physical characteristics.  But an amateur rockhound has to start somewhere and these general classifications provide a basic structure for delving into the complex geochemistry of our home planet.

Hunting Rocks

Having become enthused with agate collecting during our recent trips to Lake Superior, my wife and I have taken up the broader hobby of rock hunting.  While I have long been interested in geology, plate tectonics, natural history, rock formations and landscapes, my knowledge regarding specific types of rock has been lacking and this seemed like a good opportunity to broaden my education.

Heading to our Colorado farm, we thus took along a copy of Gem Trails of Colorado, by James Mitchell, to guide our collecting efforts.  Surprisingly, our first stop would be along the Republican River Valley on the High Plains of eastern Colorado, about 20 miles north of Burlington.  There we scoured the Tertiary and Upper Cretaceous sediments for agates, jasper, opals and other gemstones, eroded from the Rockies and carried eastward by large, meandering rivers; petrified wood may also be found in that area.  Today, we headed to Golden Gate Canyon, northwest of Golden, Colorado, where we searched outcrops of pegmatite for mica, black tourmaline and feldspar among many other colorful rocks of the Front Range foothills.

Like birdwatching and the study of wildflowers, rock hunting can be a frustrating experience for the beginner, attempting to compare samples and sightings with the limited illustrations in field guides. But, like the other disciplines of nature study, this endeavor will open our eyes to a whole new area of science and, in the process, make us better appreciate and understand the magnificent diversity of our planet.  Besides, it will provide fodder for a wide assortment of blog topics!

Crossing Parched Terrain

Traveling across the Great Plains of North America can be monotonous at times but yesterday's journey was both depressing and worrisome.  The severe heat, intense sunshine and prolonged drought of this brutal summer have produced dry and yellowed grasslands, sunburned trees and barren crop fields.  The major streams are shallow and sluggish, farm ponds have given way to mudflats and the only greenery is provided by stressed riparian woodlands, roadside weeds, tangles of prairie sunflowers and, ironically, irrigated crop circles on the High Plains.  The Flint Hills of eastern Kansas, usually covered by olive grasslands and copious wildflowers in early August, were reminiscent of the Colorado Plateau, with its sparse vegetation and dry stream beds.

Birds were rarely encountered, save the occasional flock of vultures, among the few species to benefit from the deadly drought.  Cattle huddled in the shade of trees or billboards while goats and pronghorns were the only mammals that seemed to be comfortable amidst the parched landscape.  Wind farm turbines whirled in a hot, south wind and only a few high cloud banks marred the clear blue sky.

Fortunately, intermittent monsoon showers have provided some relief along the Colorado Front Range and most of the trees and shrubs on our Littleton farm, adapted to a semi-arid climate, are alive and well.  Indeed, after eleven hours on the drought-plagued plains, it looked like the promised land when we arrived last evening.  Hopefully, late summer rains will soon bring relief to the farms, ranches and prairies of America's Heartland.

Send in the Clouds

We humans generally prefer mild, sunny weather but, after endless weeks of blazing sunshine, those of us in the Heartland appreciated the clouds that blanketed our region yesterday.  Triggered by an approaching cold front that brought severe storms to the Chicago area, the clouds did not provide much cooling but kept the intense sun at bay for most of the afternoon.

The rain, what little we received, arrived overnight and, unfortunately, skies are now clearing to the west.  Sunshine is forecast for the coming week though afternoon highs should remain in the nineties and morning lows will start dropping into the sixties.  What we really need is a prolonged period of wet, cloudy weather to resuscitate the vegetation, refill the ponds and recharge the streams but, heading into the driest months of the year, that is not likely to occur in the near future.

A glimmer of hope is offered by Tropical Storm Ernesto, now churning westward through the Caribbean.  While most forecast models take it into Mexico or Central America, there is an outside chance that it may angle northwestward through the Gulf and, just maybe, sweep its cargo of moisture across the Southern Plains and lower Mississippi Valley.  Perhaps it will park over Missouri for a week or so, producing gray skies and steady rain.  One can dream.

Cave Men: Then & Now

Often depicted as hirsute, dim-witted creatures who lived in caves and survived by brute force, our ancestors deserve more respect.  As they spread out from Africa, about 80,000 years ago, they were clearly resourceful, creative and cooperative beings, every bit as intelligent as modern humans.  Indeed, those traits spawned their migration and ensured the survival of our species.  Were it not for their resilience, we would not be here to belittle their reputation.

One wonders how many modern humans would survive if suddenly deprived of modern technology.  We may have acquired a great deal of knowledge and built shining cities of glass and steel but, in the process, have lost many of the skills that were essential to our distant ancestors.  Sadly, we have also abandoned the cooperative spirit that gave them the courage to face the many challenges of life in the wilderness.

There are, unfortunately, modern cave men.  I am not referring to primitive tribes that, cut off from the commerce and technology of modern society, retain their self-sufficiency and nature-based lifestyle.  Rather, I point to those who, for a variety of reasons, eschew the benefits of education and focus on their own narrow-minded view of humans and our place in the Universe.  Tucked within their cave of ignorance, they foment intolerance and discrimination, condemning any suggestion of compromise or cooperation.  In the end, they may undo the achievements of our distant ancestors.

Flushing Out a Killer

Watering a flower bed last evening, I flushed out a praying mantis that was lounging in the black-eyed susans.  Crawling to the top of those summer blossoms, it waited out my disturbance, gently swaying to blend with the movement of the vegetation.

Though docile and fragile in appearance, the praying mantis, one of twenty mantids in North American, is a ferocious predator, snaring insects with its barbed forelegs.  Equipped with a highly mobile "neck," two large compound eyes and three simple eyes, this hunter is very adept at locating and catching prey as small as mosquitoes; it also feeds on larger victims such as crickets and grasshoppers (and juvenile mantids) and female mantises, larger than the males, are known to devour their suitor after (or while) mating.  Since they are also active at night, praying mantises often stake out a porch light, feasting on hapless months and beetles that are drawn in from the darkness.

Pregnant females deposit their eggs in a frothy tube that is generally attached to plant stems but may be placed under the eaves of sheds and porches; this hardens into a firm egg case that is often raided by birds or mice during the winter months.  If undisturbed, the case will yield up to 200 hatchlings in the spring, all tiny replicas of the adults that died in the autumn chill.  Those not eaten by shrews, mice, snakes or songbirds will stalk our shrubs and gardens, welcome and natural agents of insect control.

Alaska's Collage of Terranes

As the Mesozoic Era dawned, 225 million years ago, only northern and northeastern Alaska were part of North America.  Since that time, numerous terranes and sub-terranes, have accreted to that primitive coast, producing the vast and varied landscape of present-day Alaska.

Many of these terranes, carried in on oceanic plates, were once part of other continents or sub-continents, having rifted away as new seaways opened.  Others formed as volcanic island arcs above subduction zones, either along the expanding coast of Alaska or elsewhere.  Still other terranes were composed of oceanic crust, trapped and lifted between colliding continental segments or scraped from the upper surface of a subducting oceanic plate.  Those terranes arriving from other regions of the globe were composed of rock much older than the sedimentary or volcanic rocks that formed along their margins at the time of accretion and possess fossils that provide clues to their site of origin. For example, the Alexander Terrane of southeastern Alaska contains Silurian rocks that harbor marine fossils also found in the northern Ural Mountains of Siberia, suggesting that the two land areas once bordered the same sea.

As the various terranes assembled, from the Triassic Period to the present day, the collisions lifted mountain ranges; on either side of these mountain corridors, downwarping of the crust produced basins that, over time, filled with erosional debris from the adjacent highlands.  In other areas, volcanism along subduction zones (which shifted southward with each new terrane accretion), produced volcanic ranges, basalt flows, igneous plutons, ash sediments and lava dikes that, today, are interspersed with the strata of the terranes.  Fault lines remain active between many of the terranes (triggering intermittent earthquakes) and volcanism continues to mold the coastline, especially along the Aleutian Chain.  Needless to say, the geology of Alaska is highly complex, a jumbled collage of strata that range in age from ancient Precambrian rock to Pleistocene gravels, that originated anywhere from the tropics to polar latitudes and that have since been lifted, folded, incised, buried and eroded by tectonic forces, streams and glaciers.