August
The High Center: Drama Visible and Invisible
The continental divide should be the great topographic crescendo of North America, a fateful point on the landscape that governs whether a falling raindrop travels to the Atlantic Ocean or the Pacific Ocean. Where the divide coincides with a narrow ridge of rock that drops precipitously on either side, the topographic drama lives up to expectations. In much of Rocky Mountain National Park, however, I look around and ask myself, where exactly is the divide? The divide meanders along the high center of the park, passing points where the drop-off is steep to both east and west, as expected, but for the most part obscure amidst the subtle topography. The high center of the park is not so much a concentration of towering peaks as a broad, gently undulating plateau at very high elevations, with individual peaks rising above the plateau.
The existence of the high center reflects hundreds of millions of years of geologic history. Each time the Rocky Mountains were uplifted, the topography was rejuvenated. Rock falls and landslides brought sediment from the hillslopes. Glaciers and rivers carried the sediment to lower elevations. As uplift slowed and erosion continued, the rivers deposited broad wedges of sediment from the mountains toward the east. Earlier iterations of the Rockies were much higher than today’s mountain range and the rivers draining these heights spread sand and gravel worn from the mountains into the Great Plains as far as what is now the Colorado-Nebraska or Colorado-Kansas border. The central part of the mountains wore down to relatively round, gentle peaks.
As movement of molten material beneath Earth’s crust caused renewed uplift, the relatively flat bedrock surfaces that had been created by prolonged weathering and erosion were lifted skyward. New glaciers and rivers cut into the flanks of the bedrock surfaces, carving deep valleys but leaving a central portion relatively unaffected—the high center.
Explaining why the continental divide in the Colorado Front Range includes some fairly flat but high-elevation landscapes leaves unanswered the question of why the Front Range, or the greater Rocky Mountains, of which the Front Range forms a part, even exist. That is a bigger geologic story.
The Mountain Rope of the Americas
The Rockies are a part of the Cordilleran Mountain system that dominates the western edge of North and South America. Cordillera comes from a Spanish word for chain of mountains, derived from an old Spanish phrase for rope. Depending on your linguistic background, you might pronounce it cord-ee-yera, or cord-i-lera. Either way, it represents one of the most impressive mountainous regions on the planet, extending nearly 11,000 miles from the Aleutian Islands to the tip of South America. The Cordillera is part of an even larger system of mountains that rings the Pacific plate, recording the tumultuous history of that portion of the planet, with segments in Antarctica, New Zealand, the western Pacific islands, and Siberia. The North American segment of the Cordillera is about 6,000 miles long, stretching inland almost 1,000 miles at its widest point at 40° N latitude, right in Rocky Mountain National Park.
Earth’s crust deforms plastically as it sinks or rebounds beneath greater or lesser weight. The crust also behaves like a brittle solid, breaking and tearing under forces created by movements within the mantle. These forces have broken the crust into six major tectonic plates and multiple lesser plates. Over the course of geologic history the plates have been an unruly bunch, crashing into one another like bumper cars in a carnival ride, then pulling away again.
The continual shifting and jostling among the plates results in different types of plate boundaries. Where two plates come together in a convergent zone, the effects on each plate depend on their relative density. A dense oceanic plate converging on a lighter continental plate gets subducted, or forced downward into the mantle. This is an extremely messy, violent process. Any less dense portions of the subducting plate, such as volcanic mountains or islands, can be scraped off and accreted onto the edge of the continental plate. A geologic map of the western edge of North America is a colorful mosaic of different types and ages of rocks left behind by the Pacific plate as it descends into the depths. The edge of the Pacific plate does not go gentle into its goodnight: it sticks in place and then moves downward in an abrupt jerk that sends seismic waves out to shake the crust for hundreds of miles around. As heat and pressure increase with depth, the subducting plate begins to melt. Some of this less dense molten rock rises back toward the surface to break through in volcanoes or to bubble up the overlying rocks with magma that cools beneath the surface as a granitic pluton. The distance inland at which the volcanoes or plutons form traces the angle of the subducting plate. A steeply plunging plate produces mountains close to the coastline. A plate going down at a shallower angle deforms the overlying surface further inland.
The forces exerted on Earth’s crust by the movements of tectonic plates through time hold the key to understanding the distribution and history of mountain ranges. All of the processes of mountain building are known as orogeny, from the Greek oro for mountain and geny for production. Most mountains are belts of deformed rocks that parallel the edges of continents because the mountains reflect the history of plate interactions along those edges. Deformed rocks can be folded where compressional forces cause the rock to bend, or faulted where compressional or tensional forces exert such abrupt stress that they break the rock. Rising magma can heat the overlying rocks, causing some minerals to melt and move in liquid form, and changing the composition and structure of other minerals in processes known as metamorphism (from the Latin meta for boundary or turning post and the Greek morph for form). Rising magma can also bow up the overlying rocks before cooling below the surface as an intrusive mass known as a pluton, from Pluto, Greek god of the underworld. Once the overlying rocks are removed by weathering and erosion, the pluton is known as a batholith if it is exposed over more than about 40 square miles. A batholith forms the core of many of the individual ranges within the Rockies, including the Front Range of Colorado.
It has taken a long time to create the complicated mountainous topography of western North America. The Cordillera reflects interactions between the Pacific tectonic plate and the Americas plate over an interval of nearly a billion years. These interactions continue today, as evidenced by volcanic eruptions and earthquakes along the west coast. Because the action has occurred along a predominantly north-south line, the Cordillera consists of mountain belts that also run predominantly north-south, with the Rockies occupying the interior belt of the Cordillera. The period between about 290 and 50 million years ago was a time of widespread mountain building throughout the Cordillera, and is sometimes known as the Cordilleran orogeny. The Cordilleran orogeny is given local names such as the Laramide orogeny, named after Wyoming’s Laramie Range. The Laramide was a long interval of deformation that began 70 to 80 million years ago and ended sometime between 55 and 35 million years ago. During the Laramide, as during earlier orogenies, stress from the subducting Pacific plate deformed the western side of North America. Now I sit on the topographic remnants of that deformation, appreciating the clarity of the August sunlight and the broad sweep of space all around me.
High Summer in the High Center
The pace of geological change is currently slow in the high center, and the area appears deceptively benign on this sunny August morning. The heroic tundra flowers are in bloom, the size of each blossom dwarfing the rest of the diminutive plant. White-tailed ptarmigan hens lead groups of swiftly growing chicks in foraging among the dwarf willows. Pikas dash about among the boulders, uttering their sharp squeaks that can be so hard to trace back to the actual animal. Marmots move at a more sedate pace, revolving their tails like crank-handles as they walk.
A yellow-bellied marmot (Marmota flaviventris) in the high center at the peak of summer.
Despite the steady activity of the animals surrounding me, I think of Whitman’s line, “I loaf and invite my soul.” The start of classes at the end of the month looms on the metaphoric horizon, but for now I simply enjoy the feeling of fieldwork gradually winding down before classes ramp up—a breathing space in the busy year. Not a hint of cloud appears in the blue sky and even the wind is loafing for the moment. The world spreads out vast as I look north toward the Mummy Range and the Medicine Bows, east toward the Great Plains and the intervening ridges silhouetted by morning sunlight, south toward Pikes Peak, and west toward an alternating pattern of mountains and high, broad basins.
Winter better represents the challenges that limit the survival of the plants and animals of the surrounding tundra. Tundra is present at the highest elevations because the heights are too cold, too dry, and too windy for trees. Grasses, sedges, lichens, mosses, clubmosses, and a few dwarf varieties of woody shrubs hug the ground, able to survive because of their adaptations to the desiccating winds, intense sunlight, and extreme cold. These plants limit their exposure by growing shorter, slenderer, less-branched stems and fewer and smaller leaves. They store more carbohydrates in their roots after the growing season ends, allowing each plant to get a jump on spring by starting its growth at colder temperatures, growing quickly, and flowering and setting fruit earlier than plants at lower elevations. Many of the plants are covered with hair that creates a layer of still air immediately next to their stomata, the minuscule openings through which the plant absorbs carbon dioxide and releases oxygen, losing some water in the process.
Some animals of the tundra adapt by migrating to lower elevations during winter, like the elk or bighorn sheep that graze the tundra plants during summer. Others hunt incessantly to keep their metabolism stoked against the cold, or hibernate during the coldest times. Marmots, in particular, can hibernate for eight months. Accumulated fat is their sole source of energy during this long period of torpor—marmots do not worry about obesity—and the temperature in a marmot’s burrow strongly influences how much fat the animal burns during hibernation. Young marmots have a faster metabolism than adults, so many of the young hibernate with littermates and share body warmth. Even so, long, cold winters decrease survival.
Ptarmigan use a different strategy, relying on layers of fat like the marmots, but also thick feathers that cover even the bird’s legs and feet. Ptarmigan can remain still for long periods of time to conserve energy, and they take advantage of the insulation of powdery snow by burrowing beneath the surface to escape the coldest temperatures and strongest winds. Every inhabitant of the tundra needs some special physiology or behavior to survive winters where the temperature can reach –21°F and wind speeds can exceed 200 miles per hour.
Hamster-sized American pikas (Ochotona princeps) are some of the liveliest inhabitants of the high center during summer, as the animals leave piles of “hay” out to dry in the sun. Beyond carefully stocking the larder, pikas’ small bodies fully covered in dense fur from the soles of the feet to the ears help them to survive winter.
Some animals survive the alpine winter by storing food. One of the most endearing sights on the summer tundra is a pika darting between sheltered crevices as it lays out tiny piles of hay in the sunshine baking the boulder fields. I find pikas adorable, but their incessant activity in August is in deadly earnest, for they do not hibernate and now is the crunch time for laying in the winter food stores that will keep them alive. Many of the calls and social behaviors that I watch with delight are actually the pikas defending their hard-earned hay piles, for which the little animals selectively harvest plants with the highest caloric, protein, lipid, and water content available.
Pikas are so well adapted to cold that they are considered early warning systems for detecting global warming in the western United States. Continued monitoring indicates that pikas are moving to higher elevations, where higher elevations exist, in an attempt to find suitable habitat and cooler temperatures: if they cannot find refuge from the heat, pikas can die in six hours when exposed to temperatures above 78°F. When you live near the top of a mountain to start with, however, it can be hard to find suitable habitat by going up in elevation. Recognition of this dilemma for the pikas, along with evidence of decreasing pika populations, led the National Park Service to start the Pikas in Peril Project in 2010. The project focuses on identifying at-risk populations and seeking solutions that may keep the pikas alive as temperatures continue to warm.
Imagining overheating pikas running out of cooler land to move up to is a grim thought and a reminder that heat can be as implacable as the tundra’s winter cold. On a summer morning, however, the world of the tundra strikes me as gentle: the air is just pleasantly warm, the hiking easy, and the views stunning. Getting caught above timberline in an August thunderstorm can provide more insight into how much happens up here. Air masses heavy with water vapor sweep inland from the Gulf of Mexico, moving across the flat interior plains with little interruption. The enormous topographic obstacle of the Rockies forces the air masses to rise, causing the water vapor to cool, condense, and fall as precipitation. The foothills of the Rockies and the middle elevations, up to about Estes Park, receive the greatest volume of rain, as well as the largest amount of water per hour. By the time the air masses rise above the high center, much of the moisture has been wrung out of them. This can be hard to believe when getting drenched in an August thunderstorm, but the storm won’t last long enough or drop enough rain to cause floods in even the small creeks present at the highest elevations. I had one memorable day of fieldwork in the high center that changed from a cloudless sky to what appeared to be the end of the world—black clouds and hail zinging in at a 45-degree angle—and then back to a cloudless sky, in just over an hour.
Blowing in the Wind
The winds coming from the east that drop nitrogen over Loch Vale, gradually acidifying the lake waters, also deposit nitrogen across the high center. Alpine soils and plants have limited ability to absorb and store nitrogen. The characteristics that allow a biological community to sequester this nutrient—thick, stable soils, abundant vegetation, a long growing season, and diverse communities of soil microbes—are absent in the alpine zone. Steep slopes, shallow, rocky soils, sparse vegetation, a short growing season, and low rates of uptake by microbes and plants all limit the ability of alpine biological communities to use nitrogen. When excess nitrogen falls from the sky as dust and with rain and snow, the excess shows up in the plants. The diversity of lichen species declines as some species die off in response to the extra nitrogen. Plant species able to take advantage of the bonanza, mainly grasses and some species of herbaceous flowering plants such as clovers, increase in number. This causes increased rates of nitrogen cycling in the soil. The effect is as though the ecosystem has been switched to high speed: nitrogen reaches saturation levels and then starts to leak everywhere—into water running off the surface and entering streams and into gases emitted from the soil during the growing season. Eventually, streams and lakes can become acidified.
Ecologists and biogeochemists study the high-elevation biological communities of the park, sleuthing out the clues that reveal subtle changes through time. These studies show that the continental divide separates more than the downward flow of rivers. The western side of the national park receives about 1 to 2 pounds of nitrogen per acre each year from atmospheric sources. The eastern side, which gets upslope winds coming off the urban areas, crop fields, and animal feedlots at the base of the mountains, receives about 3.5 to 7 pounds per acre each year. The “about” preceding these numbers reflects very local differences. Half of the annual nitrogen deposition in the park occurs during the nine months of winter, when snow blown across the landscape by strong winds accumulates in lee areas and then melts, releasing its load of nitrogen. As a result, some sites receive up to 9 pounds of nitrogen per acre. Not surprisingly, these sites show the greatest response to enhanced nitrogen. By 2003, long-term records of alpine plant species indicated significant changes in the abundance of individual species during the preceding twenty to fifty years. Seventy-five percent of the increased east-side soil nitrogen can be accounted for by increased nitrogen deposition associated with human settlement of the regions beyond the national park. The remainder appears to result from global increases in nitrogen released to the atmosphere by human activities.
Despite the lower population density of the western United States, the region is more urbanized than even the mid-Atlantic portion of the country. Eighty-six percent of people in the western United States live in cities and the entire region has experienced high population growth since the 1970s. Although the western part of the country as a whole has relatively low background rates of nitrogen deposition, areas downwind from cities, such as Rocky Mountain National Park during spring and summer, are hot spots of elevated nitrogen deposition.
Rocky Mountain National Park is not unique in this respect. A comprehensive survey of eight national parks in the western United States indicates that, despite our best intentions to set aside national park lands “to conserve the scenery and the natural and historic objects and wildlife therein, and … to leave them unimpaired for the enjoyment of future generations,” as stated in the 1916 National Park Service Organic Act establishing the national park system, the parks exist within a greater landscape and air-scape beyond the control of the national park service. Air, vegetation, and snow at Glacier National Park contain high concentrations of pesticides coming from agricultural lands outside the park, as well as highly toxic synthetic compounds such as PCBs associated with an aluminum smelter. Air, vegetation, and snow in Olympic National Park contain mercury, PCBs, and pesticides. The story is repeated over and over, at Mount Rainier, Sequoia and Kings Canyon, North Cascades, Grand Teton, Crater Lake, Lassen Volcanic, Yosemite, Great Sand Dunes, Bandelier, and Big Bend National Parks. Even the far-flung reaches of the national park system are not so far for atmospheric transport: Wrangell–St. Elias, Glacier Bay, Katmai, Noatak, Gates of the Arctic, and Denali in Alaska contain historically used pesticides, mercury, and other contaminants, albeit at lower levels than national parks in the lower Forty-Eight. Every national park in the country in which scientists have assessed pollutants shows some level of contamination from sources outside the park boundaries.
The trends revealed by these studies suggest the importance of long-term monitoring and the importance of comparing diverse sites across the country. Acid rain received a great deal of attention starting in the 1970s because huge swaths of forest in regions downwind of industrial sources of sulfur and nitrogen began dying. The death of a forest is analogous to late-stage diagnosis of aggressive cancer: the problem has been developing for a long time and it is difficult to effectively halt the disease by the time it becomes obvious. In the case of forest die-off or lake eutrophication, the levels of acidity in the soil and water have increased over decades, triggering a cascade of changes in chemistry, microbial communities, and nutrient processing that cannot be quickly reversed. If long-term monitoring allows us to detect problems before they reach a crisis stage, there is hope that we can act to alleviate the situation causing the problem. Knowledge is only half the battle, however: knowledge has to lead to action.
Invisible Engineering
The high center epitomizes the invisible changes occurring within Rocky Mountain National Park. From the air come the nitrogen, mercury, pesticides, and PCBs that leave no obvious trace on the landscape but nonetheless insidiously work their way through the ecosystem, changing soil, water, and biological communities. And deep below lies the equally invisible engineering that sends water from the western side of the continental divide flowing to the east.
The national park map includes a dashed blue line, straight as a ruler, from Grand Lake on the west to a site labeled East Portal, just outside the park boundary on the east. This is the Alva B. Adams Tunnel, one component of the massive Colorado–Big Thompson Project that transfers water from west to east.
Water users have been eyeing Grand Lake as a source of water for the eastern slope for more than a century. An 1889 study evaluated the idea of cutting a canal across the mountains from the lake to South Boulder Creek. Proposals to divert Colorado River water directly through the Rockies via a tunnel date to a 1905 engineering class project at Colorado State College. The original proposal involved diverting water from Grand Lake to Moraine Park. The idea was revived in 1933, but met with strong objections from the park service. The park service worried about problems ranging from inadvertent draining of high-elevation lakes if the tunnel pierced fractures in the bedrock, to the unsightly disruption associated with reservoirs, power stations, and electrical lines. However, the politically powerful Bureau of Reclamation supported the project and state politicians and local newspapers aggressively promoted the idea.
The compromise solution was to build the diversion, but make it less visible. Instead of a surface ditch, the water went into an underground tunnel. The eastern portal of the tunnel was moved to a site just outside the park boundaries that is less visible than a portal at Moraine Park would have been. Grand Lake is a natural lake and the artificial reservoir of adjacent Shadow Mountain Lake was created in part to allow pumping from this water body so that the water level in Grand Lake could remain constant. Franklin Roosevelt approved the project in 1937 and the first water flowed eastward through the 13.1-mile-long tunnel in June 1947.
Now, when I climb the Flattop Mountain, North Inlet, or Tonahutu Creek Trails up to the high center, or stroll along one of the spur trails from Trail Ridge Road, I cannot see it, but some 3,000 feet below me is a tunnel just under 10 feet in diameter that sends up to 550 cubic feet per second of water under the continental divide.
Just as the continental divide is the starting point for the journey of a metaphorical drop of water flowing to the Atlantic or the Pacific, the invisible water engineering of the Adams Tunnel is the starting point for the changes in flow that have altered rivers across the western United States. On the eastern side, the more abundant water released from dams at a steady rate throughout the growing season has transformed the Platte River of the western prairie from a broad, shallow, braided channel to a narrow stream meandering through densely growing riparian forests. On the western side, the steady suck of the Colorado River’s water into thousands of canals and pipes has shrunk the once-mighty river into a salty trickle that no longer reaches the ocean in most years. The Adams Tunnel is not the only water engineering in the Platte and Colorado River basins, but it exemplifies the utilitarian hubris of water use in the western United States by rearranging water right at the start of each watershed. This history of altering rivers to facilitate human water consumption, navigation, and flood control is part of the reason that various agencies in federal and state governments now spend a great deal of time and money trying to restore rivers in each watershed.
Acting on Knowledge
Humans are hardly absent from the high center. Trail Ridge Road is a high-use corridor, complete with exhaust fumes, noise, and thousands of hikers. The road dramatically increased access to the tundra and was a controversial alteration of the high center. The first, unpaved road was built during 1929 to 1932, a period of increased emphasis on automobile access to national park interiors that also saw construction of the Sylvan Pass road in Yellowstone, Going-to-the-Sun highway in Glacier, and the Wawona road and tunnel in Yosemite. When Trail Ridge fully opened in 1933, 83,000 autos entered Rocky Mountain National Park. By 1938, that number increased to 200,000 cars. Steadily increasing visitor numbers after World War II seriously strained national park facilities across the country, and in 1956 the National Park Service began a ten-year program known as Mission 66. Among the infrastructure improvements implemented during this program was the paving and widening of Trail Ridge Road. Critics charged that making travel in the national park more attractive and comfortable detracted from the area’s naturalness, as well as luring more visitors (3 million people a year by 1978) into the high center. The critics were right, but the road is now a fait accompli around which the park service must design management to minimize direct human impacts to the tundra.
Numerous signs along Trail Ridge Road emphasize the fragility of the tundra, where thin soils exposed by trampling feet can erode readily in the wind, but plants grow back to cover the soil only very slowly. No one realized exactly how slowly until a woman named Beatrice Willard decided to systematically study the tundra. Willard received an undergraduate degree in biology from Stanford University in 1947. She dreamed of becoming a naturalist-interpreter for the National Park Service, but such a position was largely closed to women during the 1940s. But, where there’s a will, there’s a way. Bettie Willard moved to Colorado in 1957 to attend graduate school at the University of Colorado, just as the park service was getting ready to start Mission 66. She began working along Trail Ridge Road, which at that time had few formal parking areas or trails, allowing visitors to wander freely. Willard established permanently fenced sites in alpine areas near Forest Canyon Overlook and Rock Cut and monitored these plots annually for almost forty years. The resulting research constitutes one of the longest known records of alpine plant recovery and indicated that hundreds of years would likely be needed for full recovery of alpine areas trampled to bare soil by the feet of park visitors. Willard found that tundra sites trampled by people during the course of one year could recover nearly completely within four years, whereas areas trampled for decades would need a long, long time to once again accumulate the small mineral grains mixed with dead plant parts—soil—needed to support living plants. As Willard wrote in a 1971 paper, “The time-factor in tundra recovery is quite shocking.” Working with park service staff, Willard helped to develop trails that would channel future visitors like water flowing in a river network, thus limiting the impact of human hikers.
Willard taught at the Colorado School of Mines for many years and became famous for “belly botany” field courses, during which she had students lie on their stomachs to observe the details of alpine plants. She also wrote several technical papers on her research in the park, one of which starts with a wonderful opening line: “No civilized society has learned how to add Man to the landscape without robbing subsequent generations of resources and opportunities that are vital to their well-being” (Willard and Marr, 1970, p. 257). By teaching generations of university students, as well as leaders in business, industry, and government during her time on the President’s Council of Environmental Quality, Bettie Willard did as much as anyone could to add humans to the landscape without robbing subsequent generations. The woman who had a hard time finding a place with the National Park Service during the 1940s because of her gender was eventually presented with the Outstanding Environmental Leadership Award from the United Nations.
The presence of alpine vegetation in Rocky Mountain National Park may also be endangered by warming climate. Tundra derives from a Finnish word indicating a land with no trees, but the trees are waiting on the margins. Ecologists predict that every degree of increase in average air temperature will allow the tree line to encroach on the tundra by 250 feet. Only a few degrees warmer—easily within the range that climate scientists consider a real possibility—and the tundra will vanish. When I think of the pleasure I have experienced in watching pikas and marmots on the tundra, or in paddling among little chunks of glacial ice snapping and popping as they melt and release air bubbles in front of Greenland’s tidewater glaciers, I paraphrase Aldo Leopold’s famous phrase: I am glad that I shall never be young without frozen country to be young in.
Pondering the largely invisible changes far overhead and beneath my feet as I walk the tundra of the high center, I come back to the meaning of wilderness. What does wilderness mean in this paradox of an altered and managed ecosystem that is nonetheless largely set aside from the most obvious human alterations? Do the changes in alpine soils and vegetation caused by nitrogen deposition really matter? Probably. Time will tell, but then it may be too late on a timescale relevant to humans to reverse or mitigate those changes.
The complexities and uncertainties in ecosystem response to atmospheric deposition and to manipulation of water supplies make it difficult to predict these responses and to manage for them, but they also give us reason to hope. Ecosystems are resilient. Recent research indicates that urban streams preserve more ability to support aquatic life and to purify polluted water through natural processes than previously thought. Forest soils and vegetation can gradually recover if the acidity of precipitation is reduced. Reducing levels of phosphates in household detergents during the 1970s resulted in noticeable improvements in water quality across the country. My ruminations always return me to the thought that we can mitigate the damage we have done in the past, but only if we work at it: knowledge has to lead to action.