Opposing Winds Help Shape Great Sand Dunes National Park

When you think of the Rocky Mountains, sand dunes are probably not the first thing that come to mind. While driving across southern Colorado earlier this month, however, giant white sand dunes glimmered in the distance. No, it was not a mirage; it was Great Sand Dunes National Park and Preserve.

Sprawling across the arid San Luis Valley between the San Jose Mountains to the west and the Sangre de Cristos to the east, the dunes cover 30 square miles and rise as high as 750 feet. They are the tallest dunes in North America and were formed, and continually maintained, by a complex interaction of geology and weather.

Over the millennia, according to the National Park Service, rocks from the surrounding mountains eroded and their sandy sediments were transported by stream to the valley floodplain. Prevailing southwesterly winds then carried the sand grains toward a low curve in the Sangre de Cristo Mountains, where they accumulated in a natural pocket.  On occasion, when the wind direction reverses during storms, the sand is pushed back toward the west. This process causes the dunes to grow vertically.

Two mountain streams, the Medano and Sand Creeks, also border the dunes. They capture sand grains from the eastern side of the dunes and carry them back to the valley floor.  This effectively recycles the sand and re-exposes it to the winds.

While the forces of wind and water are continually reshaping the massive dunes, they essentially remain in the same position.

Sand dunes nestled against the foothills of the Sangre de Cristo Mountains, Great Sand Dunes National Park, CO.  Image Credit The Weather Gamut.

Massive sand dunes nestled against the foothills of the Sangre de Cristo Mountains, Great Sand Dunes National Park, CO.  Image Credit: The Weather Gamut.

Air Quality Concerns in Great Smoky Mountains National Park

Straddling the border of North Carolina and Tennessee, Great Smoky Mountains National Park protects 800 square miles of the southern Appalachian Mountains. It is the largest federally protected upland landmass east of the Mississippi River.  Air pollution, however, does not recognize these human-drawn borders. While traveling in the Smokies recently, I learned more about the air quality issues facing this country’s most visited national park.

According to the NPS, most of the air pollution impacting the park originates outside its boundaries. Emissions of sulfur dioxide and nitrogen oxides from power plants, factories, and vehicles are the main sources. Carried by wind to the southern Appalachians, the height of the mountains and the prevailing weather patterns of the region tend to trap the pollution in and around the park.

Originally named for its naturally occurring smoke-like blue haze, the park in recent years has been shrouded by unnatural white smog. Produced by tiny sulfate particles – released into the air by the burning of fossil fuels – the smog scatters light and reduces visibility. It has degraded views from the park’s scenic mountain overlooks and dulled its signature blue haze. Since 1948, according the NPS, human-made pollution has decreased average visibility in the region by 40% in winter and 80% in summer.

Ground level ozone, formed when nitrogen oxides react with heat and U.V. light, is known to have negative impacts on human health.  In the Smokies, it is also injuring trees and plants. Damaging leaves, it reduces photosynthesis and limits a plant’s ability to produce and store food.  As a result, they are more susceptible to disease, insects, and extreme weather events.

Acid rain is another problem for the park that is rooted in air pollution. It develops when sulfur dioxide and nitrogen oxides react with water and oxygen in the atmosphere to form solutions of sulfuric acid and nitric acid. This type of precipitation alters the chemistry of forest soils and streams. It jeopardizes the health of entire ecosystems, as a large array of species – from fish to trees – cannot adapt to the more acidic conditions. The average pH of rainfall in the Smokies, according to the NPS, is 4.5. That is 5–10 times more acidic than the pH range of normal rainfall.

While air quality issues in the park – like much of the rest of the country – have improved in recent years, it still remains a serious problem. Addressing the matter, the NPS says: “The Park Service is working with state regulatory agencies, the Environmental Protection Agency, and industrial and utility interests to develop a comprehensive plan to prevent future damage through such measures as offset programs, the use of improved technology, and determination of emission caps and government standards for various pollutants. To remedy air pollution problems at the park, additional reductions of nitrogen oxides and sulfur dioxide are necessary.”

The Blue Haze of the Great Smoky Mountains

Traveling in North Carolina and Tennessee recently, I had the opportunity to visit Great Smoky Mountains National Park. While renowned for its “wondrous biodiversity”, the park’s name is derived from a localized atmospheric phenomenon.

The Cherokee, who originally inhabited the area, called the mountains, “Shaconage”, meaning “place of the blue smoke”. It refers to the smoke-like bluish haze that hovers over the park’s rugged peaks and valleys, especially after a rainstorm. According to the NPS, it is a natural by-product of plant transpiration.

While all trees and plants exhale water vapor, the conifer trees in the park also emit terpenes – a naturally occurring organic compound. Released in large quantities, the mix of terpenes and moisture react with natural low level ozone molecules to form tiny particles that scatter blue light. As a result, the mountains appear to be bathed in a gauzy blue mist.

In recent years, according to the NPS, human-made air pollution has been obscuring the Smokies’ signature blue haze.

View of blue haze in Great Smoky Mountains National Park.  Image Credit: NPS

View of the bluish- haze in Great Smoky Mountains National Park. Image Credit: NPS

Alaska’s Glaciers and Climate Change

Glaciers are dynamic.  Over time, they advance or retreat depending on climatic conditions.  They form, and spread, when more snow accumulates in the winter than melts in the summer. Since the end of the Little Ice Age in the mid-1800s, most glaciers have been either stable or in slow retreat.  In the last half century, however, that rate of retreat has increased.

This summer, I had the opportunity to travel around Alaska. While there, I visited a few of its nearly one hundred thousand glaciers and learned more about how they are responding to climate change.

According to the U.S. Fish and Wildlife Service,  Alaska’s  statewide  glacial  mass  balance – the net gain or loss of ice – has been negative since the middle of the 20th century.  While conditions at individual glaciers vary, the majority are melting. Recognizing that natural variables like the Pacific Decadal Oscillation (PDO) and El Nino Southern Oscillation (ENSO) have always affected Alaska’s glaciers, most scientists agree that human-caused global warming has accelerated glacial retreat across the state.   Earth’s average temperature increased 1.4°F in the last century, but Alaska is warming even faster.  The E.P.A. reports that Alaska’s average temperature has increased 3.4°F in the past fifty years with winters warming by an average of 6.3°F.  These warmer temperatures coupled with shifting precipitation patterns are causing glaciers to both shrink in length and thin in volume.

A striking visual example to this process is Exit Glacier in Kenai Fjords National Park. It is one of forty glaciers in the park that flow out of the Harding Ice Field, but is the only one easily accessible by foot. As such, the trail leading up to it is marked with signs that point out the glacier’s previous extent and progressive retreat over nearly two hundred years. The first sign, 1815, is now over one and a half miles from the current terminus.  According to the National Park Service, this glacier has been receding at a rate of forty three feet per year, on average.  Between September 2011 and October 2012, however, it retreated one hundred thirty three feet.

While shrinking glaciers in Alaska may seem like a remote environmental issue, they have far reaching impacts. A recent study by NASA and the University of Alaska – Fairbanks found that the state’s melting glaciers are one of the largest contributors to rising global sea levels.

Exit Glacier with melt water running off into the outwash plain.  Image Credit: The Weather Gamut

Exit Glacier with melt water running off into the outwash plain.                                                  Image Credit: The Weather Gamut

Sign along the Exit Glacier trail that marks the location of the terminus in 1926. The glacier's current position is visible in the background.  Image Credit: The Weather Gamut

Sign along the Exit Glacier trail that marks the location of the terminus in 1926. The glacier’s current position is visible in the background behind the trees.                                                       Image Credit: The Weather Gamut

The progressive retreat of Exit Glacier in Kenai Fjords National Park, Alaska.

Mapping the progressive retreat of Exit Glacier in Kenai Fjords National Park, Alaska.                     Image Credit: NPS

Denali’s Wood Frogs Freeze for the Winter

While traveling in Alaska recently, I had the opportunity to visit Denali National Park and Preserve.  Its landscape, which includes Mt. McKinley – the highest mountain in North America – and its diverse wildlife were nothing short of impressive.  However, it was the tiny wood frog – the park’s only amphibian – that peaked my curiosity when I learned how it survives the region’s subarctic winters.

Situated at roughly 63°N latitude, winters in Denali are long and extremely cold.  From October to March, temperatures can range from 20°F to as low as -40°F.  These cold conditions drive many creatures to hibernate in dens or migrate south. The wood frog, however, makes it through winter by burrowing into leaf litter and literally freezing solid until spring.

According to wildlife biologists, a wood frog responds to falling temperatures by converting glycogen in its liver into glucose (sugar) and pumping it throughout its body.  Acting like a natural anti-freeze, the glucose lowers the freezing point of water inside the frog and protects its tissues and organs.  As temperatures continue to drop, however, the frog does eventually freeze.

Throughout the winter, the frog is essentially lifeless.  Its heart stops beating and it does not breathe.  Yet, as temperatures rise in spring, the frog thaws and comes back to life. While scientists are not exactly sure how this amazing resurrection works, they have noted that the wood frog’s heart and liver freeze last and thaw first.

Although the wood frog can be found across North America, the Alaskan wood frog is known to endure colder temperatures and freeze for longer periods of time than its southern cousins.  It is also the only frog found north of the Arctic Circle.


Wood Frog

Image Credit: NPS

Weather History: Death Valley Heat Record

One hundred years ago today, the temperature at California’s Furnace Creek in Death Valley National Park soared to 134°F.  To this day, that is the highest air temperature ever recorded on Earth.

Situated in the Mojave Desert and 282 feet below sea level, Death Valley is the lowest and driest place in the United States.  Its unique geography traps hot desert air and helps to heat it even further.  While the area does have seasons, summer is extremely hot.  From June through August, daytime highs in the triple digits and over-night lows in the 90s are not uncommon.

The heat wave that gripped the southwestern U.S. last month had some people thinking the Death Valley record might be broken, especially when the temperature reached 129°F on June 30th.  While this set a new monthly record for June, the century old world record still stands.

Death Valley, CA

Death Valley, CA

Image Credit: NPS

Floods Nurture Congaree National Park

Floods are often thought of as disasters, especially when people and property are harmed. In nature, however, some ecosystems thrive on periodic flooding. While traveling in South Carolina last week, I had the opportunity to visit one such place – Congaree National Park.

Situated in the floodplain of the meandering Congaree and Wateree Rivers, the park protects the largest expanse of old growth bottomland hardwood trees still standing in the southeastern United States.  It is home to a dazzling array of biodiversity, including a number of champion trees – tress that hold the size record for their species.  These include a bald cypress with a circumference of twenty-seven feet and a loblolly pine standing one hundred seventy feet tall.  These trees would not be able to flourish without the moisture and nutrient–laden sediments that flood waters bring to the forest floor.

This floodplain forest is typically inundated by water several times a year. During my visit, the park was about 90% flooded as a result of recent heavy rainfall on top of an already wet spring.  It was an impressive sight.

The elevated boardwalk trail in Congaree NP disappears into high flood waters.

The elevated boardwalk trail in Congaree NP disappears into high flood waters.

Image Credit: The Weather Gamut

Above the Clouds on Haleakalā

While traveling among the Hawaiian Islands, I had the opportunity to visit Haleakalā National Park.  Ascending its volcanic slopes, I was struck by its summit region known as “kua mauna”, the land above the clouds.  Its unique view is made possible by an elevated temperature inversion.

In the troposphere, the weather layer of our atmosphere, air temperature usually decreases with height.  An inversion occurs when something causes that situation to reverse and allows air temperature to increase with height.

At Haleakalā , the inversion is caused by a large-scale subsidence in the Trade Winds.  Blowing from centers of high pressure across the Pacific, cool, dense air aloft is warmed by compression as it descends to lower altitudes.  In opposition, solar heating warms air near the surface allowing it to rise and cool, forming clouds.  When these cool clouds meet the warmer air above them, an inversion layer is formed.

The inversion layer acts like a cap for cloud convection.  Therefore, the summit of Haleakalā (10,023 feet), rising above the inversion altitude, stands out like an island in a sea of clouds.

View from the summit of Haleakalā, Maui, Hawai'i

Photo Credt: MF at The Weather Gamut

Weather Journal of Lewis and Clark

I recently came across the book, Lewis and Clark: Weather and Climate Data from the Expedition Journals, edited by NWS meteorologist Vernon Preston.

Ever since my visit to the Jefferson National Expansion Memorial (Gateway Arch) in St. Louis, Missouri, I have been interested in the amazing journey of Meriwether Lewis and William Clark.  Between May 1804 and September 1806, these explorers traveled 4,162 miles from the Mississippi River to the Oregon Coast. Commissioned by President Thomas Jefferson, the “Corps of Discovery” had goals that were both scientific and commercial. Following their mandate, the expedition journals record the geography, flora, fauna, weather, and climate of the then uncharted territory of the American West.

Preston’s book focuses in on the weather and climate data found in the well-ordered journals.  It highlights both the positive and negative impacts the weather had on the expedition as well as how the explorers dealt with the elements. The book also supplements the journal data with route descriptions and historical maps.

A highly detailed book, it would be at home in the library of anyone interested in both meteorology and history.

Route of the Lewis and Clark Expedition

Image Credit: Wikipedia

Ancient Climate of the Tall Grass Prairie

While traveling in the Mid-West not too long ago, I enjoyed a visit to the Tall Grass Prairie National Preserve in the Flint Hills region of Kansas. When you hike through its beautiful open landscape, the limestone beneath the grass stands out as evidence of past climate change.

Climate can shape the geology of a region in many ways.  In this case, the freezing and thawing of glaciers affected the existence of an ocean that covered much of present-day Kansas and Oklahoma.  Today’s vast “sea of grass” was once the bed of the Permian Sea. According to scientists, this shallow sea rose and fell numerous times during the Permian Period of the Paleozoic Era, about 251-299 million years ago.

This ancient sea sustained an array of aquatic-life, including fish and plants.  Just like today, these marine organisms took calcium carbonate out of the water to form their shells and skeletons.  After they died, these prehistoric sea creatures fell to the ocean floor where their stored calcium carbonate accumulated to form limestone over time.

These layers of sedimentary rock and the fossils they contain give us a much different view of America’s heartland than we are used to today.

Open landscape at the Tall Grass Prairie National Preserve, Kansas.

Limestone at Tall Grass Prairie National Preserve, Kansas.

Photo Credit: MF at The Weather Gamut