Wind Cave National Park and the Science Behind What Makes the Wind Blow

I recently visited Wind Cave National Park in South Dakota, which protects a beautiful expanse of the Northern Great Plains as well as one of the largest and most complex cave systems in the world. While well known for its geology, the park’s namesake feature is also an excellent example of the science behind a basic weather phenomenon – wind.

Wind, which is air in motion, is the result of differences in atmospheric pressure. These pressure differences are caused by the temperature differences created by the uneven heating of the Earth’s surface by the Sun.  Several factors contribute to this unbalanced process, including cloud cover, large bodies of water, topography, and vegetation.

As the surface warms, air heats and rises, creating an area of low pressure. To fill that void, air from an area of relatively higher-pressure rushes in, creating a flow of air that we recognize as wind. The greater the pressure differences between these two areas, the stronger the breeze.

Atmospheric pressure conditions at the cave entrance during my visit. Credit: Melissa Fleming

At Wind Cave, given its vast size, the air pressure inside the cave is constantly working to equalize with that above ground. Therefore, when there is an area of high pressure at the surface, the wind will blow into the cave. If there is an area of low pressure on the surface, the wind will blow out of the cave. For this reason, the cave is described in the oral histories of the Lakota – a Native American tribe who consider it scared – as “the hole that breathes cool air”.

Park Ranger demonstrates the flow of air coming out of the small cave entrance with a ribbon. Credit:RVDreamLife

While other large cave systems can generate barometric winds, those at Wind Cave are more noticeable because of the small size of its entrance. As the Venturi Effect shows, when space is constricted, air will flow faster. Legend says that the first non-native settlers to discover the cave – two brother named Jesse and Tom Bingham – did so by accident when the wind from its entrance blew the hat off one of their heads in 1881.

According to the NPS, winds at the cave’s natural entrance have reached up to 25-mph.

Wind Cave National Park, SD. Credit: Melissa Fleming

Road Trip Highlights US Environmental History and Shows Big Changes are Possible

Last week, I was in Pittsburgh, PA to serve as a Mentor at a Climate Reality Project training event. Having never been in that part of the country before, I spent a few extra days to explore the area. The overall experience felt like a road trip through US environmental history and was a great reminder that large-scale changes are possible, especially in this era of climate policy backpedaling.

First stop: Donora, PA. This Pittsburgh suburb was the site of the “Killer Smog of 1948”. As the longtime home of the Donora Zinc Works Factory and the American Steel and Wire Plant, smoke-filled skies were not unusual here in the early part of the 20th century. In October 1948, however, the air turned deadly. An inversion layer, a weather phenomenon where the temperature in the atmosphere increases with height instead of decreasing, trapped emissions from the factories. The sulfuric acid, nitrogen dioxide, fluorine, and other poisonous gases created a thick, yellowish smog. It hung over the area until the weather pattern changed five days later. As a result, twenty-six people died and thousands of others became ill.

This tragedy garnered national attention and spurred federal regulations on air pollution. In 1955, Congress provided funding for pollution research and later passed the Clean Air Act of 1963. In 1970, the EPA was created and Congress passed the Clean Air Act Amendments, which established national air quality standards.

Donora is proud of their role in this change in national environmental policy. Outside of their local Historical Society/Smog Museum is a sign that says “Clean Air Started Here”.

Another highlight of this trip was Cuyahoga Valley National Park in northeastern Ohio. Established as a National Recreation Area in 1974 and upgraded to a National Park in 2000, it reclaimed and now preserves the natural landscape along twenty-two miles of the Cuyahoga River between Akron and Cleveland, OH. While relatively small, the river is an icon of American environmental history.

Starting in the late 1800s, the river became highly industrialized. For more than a century, the steel mills and factories that lined its banks dumped untreated waste directly into the river. The Cuyahoga became so polluted that it caught on fire thirteen times.

The last time was June 22, 1969, when sparks from a passing train ignited the oil and debris floating in the water. This fire, while not the largest or deadliest in the river’s history, caught the attention of Time Magazine and became national news. Appearing in their August 1 issue, the article described the Cuyahoga as a river that “oozes rather than flows”.

During the late 19th and early 20th century, river fires were common and seen as the price of industrial progress and prosperity. By the 1960’s, however, that way of thinking was starting to change. The country was becoming more environmentally aware and the Cuyahoga River fire put a national spotlight on the need to protect waterways from industrial pollution. The event helped to galvanize the Water Quality Improvement Act of 1970 and the Clean Water Act of 1972.

In the years since, the Cuyahoga River has made an amazing comeback. Bald Eagles – a symbolic emblem of this country – have returned to fish its waters and nest along its banks. In 1998, it was designated as an American Heritage River to recognize its historical significance.

Today, our environmental challenge is the carbon pollution that drives climate change. Its solution, as with conservation issues in the past, lies with policy adjustments. While these types of large changes can sometimes seem impossible, history reminds us that they are not. All that is required is the will to act. As Nelson Mandela once said, “It always seems impossible until it’s done”.

Cuyahoga River, past and present. Credit: Cleveland State University Library

A Look at Why Death Valley is the Hottest, Driest, and Lowest Place in US

Death Valley National Park is famous for being the hottest, driest, and lowest place in the United States. The interesting thing about all these extremes, as I learned during a recent visit, is how they interconnect.

Situated in eastern California near the Nevada border, the park’s topography is known as basin and range. This is where the earth’s crust is rifting apart, creating mountains in some areas and deep basins in others. Death Valley is a long, narrow basin that reaches a depth of 282 feet below sea level. It is also in the rain shadow of four different mountain ranges to the west – the Coastal Range, the Sierra Nevada, the Argus Range, and the Panamint Range.

As storms move inland from the Pacific, they must rise up and over each range. In doing so, they cool and their water vapor condenses into rain or snow that falls on the western side of these mountains. By the time a storm system reaches Death Valley, it has lost most of its moisture. The average annual rainfall in the park, according to NOAA, is just 2.36 inches.

These dry conditions, along with the valley’s below-sea-level elevation, help to produce the park’s famous heat. With cloud free skies and sparse vegetation, a maximum amount of sunlight can reach the ground. The rocks and parched soil absorb the heat and radiate it into the air. The warm air rises but becomes trapped by the steep valley walls. After cooling slightly, it is recycled back toward the valley floor where it is heated even further by atmospheric compression. During the summer months, this process generates hot winds and sizzling temperatures. The average high temperature in the park ranges from 67°F in January to 116°F in July. The hottest temperature ever recorded was 134°F on July 10, 1913 – a world record.

Looking ahead, as the climate changes, the southwestern region of the US is expected to become even hotter and drier. It seems like only a matter of time before Death Valley breaks its own heat record.

At 282 feet below sea level, Basin in Death Valley National Park is the lowest point in the US. Credit: Melissa Fleming

Climate Change is Changing Glacier National Park

Glacier National Park (GNP) in western Montana is on the verge of losing its namesake features to climate change. Given this fact, I made a point to visit the park this summer to see what remains of its famous glaciers before they completely melt away.

According to the National Park Service, the area that is now GNP was home to 150 glaciers at the end of the Little Ice Age in 1850. Today, because of rising global temperatures, only 25 remain and most are mere vestiges of what they once were. Looking ahead, if the current rate of melting continues, all of the park’s glaciers are expected to disappear by 2030, if not sooner.

Glaciers are dynamic entities that respond to changes in temperature and precipitation. They advance when more snow accumulates in the winter than melts in the summer. When this process is reversed, they retreat. Sadly, the new norm in GNP includes warmer summers and a decreasing snowpack.

The USGS, which monitors the park’s glaciers, reports that the mean annual temperature in GNP has increased 1.33°C (2.4°F) since 1900. That is nearly twice the global average. The park also now sees 16 fewer days each year with below-freezing temperatures. These warmer conditions mean that more precipitation is falling as rain rather than snow.

Beyond aesthetic changes to the landscape, the shrinking glaciers and reduced snow pack mean less melt water for the region and therefore warmer and drier summers. This, in turn, affects soil moisture and the proliferation of wildfires. It also has serious ramifications on the availability of fresh water for drinking and irrigation.

In arid regions, like the American West, people depend on mountain run-off from melting glaciers and winter snow packs for the majority of their fresh water. In western Montana, according to the NPS, snowmelt accounts for 60-80% of the annual freshwater supply. As temperatures rise and the stores of this precious resource dwindle, competition for it is expected to increase.

But, glaciers are not the only things changing in GNP. As the atmosphere heats up and the ice retreats, the park’s various ecosystems are also being reshaped. Sub-alpine trees are moving upslope replacing alpine meadows, for example. This changing distribution of vegetation affects the type of wildlife the park can support. While some animals can adapt and move upslope with their habitat, others, like the pika – a small furry relative of the rabbit who lives at high elevations and cannot survive temperatures above 75°F – already live at the end of their range and have no place to go.

The NPS has no plans to change the name of Glacier National Park.

"Repeat Photography", a USGS project, documents the changes to GNP's glaciers over the years. Credit: USGS/NPS

Images of Sperry Glacier from “Repeat Photography”, a USGS project, that documents the changes to GNP’s glaciers over the years. Credit: USGS/NPS

Giant Sequoias Challenged by Climate Change

Many things in nature are adapted to certain climate conditions. That said, some are choosier than others. Giant Sequoia trees, the largest living organisms on the planet, need a “Goldilocks” type of environment to grow and reproduce. Visiting Sequoia National Park recently, I had the opportunity to learn more about the climate requirements of these amazing trees.

Needing conditions that are not too hot and not too cold, as well as not too wet and not too dry, Giant Sequoias grow naturally in only one place on Earth. That unique place is a narrow band about 70-miles long on the western slopes of California’s Sierra Nevada Mountains known as the Sequoia Belt. According to the National Park Service (NPS), these trees only grow at elevations between 5,000 and 7,500 feet. Temperatures above 7,500 feet are usually too cold and conditions below 5,000 feet are too dry. Within this limited range, about 75 groves reveal where conditions for the massive trees are just right.

These ideal conditions are produced by a combination of weather and topography. When moisture-laden air from the Pacific runs into the Sierras, it rises and cools. On average, it cools about 3.6°F for every 1000 feet it rises. Since cooler air holds less moisture than warm air, the moisture is dropped as rain and snow over the mountains with precipitation amounts generally increasing with elevation. While California is in the midst of a multi-year drought, the NPS says the area around Giant Forest (elevation 6400 feet) usually gets an average of 44 inches of precipitation a year. It also typically sees only one day a year with temperatures below 10°F.

Compared to other sites within a five mile radius, the average conditions in Giant Forest are perfect for the giant sequoias. Upslope, Emerald Lake (elevation 9200 feet) gets 59 inches in average annual precipitation and sees around ten days a year with temperatures below 10°F. Downslope, Ash Mountain (elevation 1700 feet), only sees about 26 inches of precipitation a year and the temperature reportedly never falls below 10°F.

Given the narrow natural range in which these giant trees are able to thrive, they face serious challenges from climate change. As temperatures increase, more precipitation is coming down in the form of rain instead of snow. This reduces the snowpack and the subsequent spring and summer melt water available to the trees during the region’s dry season. While the resilient mature sequoias – some are over 3000 years old – are not in immediate danger, researchers say these big trees were not made to withstand decades of drought. The younger trees – seedlings and saplings – on the other hand, face a more difficult struggle for survival. The drier conditions make it harder for them to develop robust root systems and also leave them more susceptible to wildfires, which are projected to increase.

Given the impressive age of some of these trees, they must have endured natural climate fluctuations in the past. This time, however, the human caused change is happening very quickly and is forecast to produce conditions unfamiliar to even these ancient giants. According to the US National Climate Assessment, the southwest – which includes California – is normally the hottest and driest part of the country, but climate change is making it even more so. The report shows that 2001 through 2010 was the region’s warmest decade on record with temperatures almost 2°F above historic averages. Looking ahead, it projects continued increases in average annual temperature and a decrease in precipitation. In the meantime, scientists continue to monitor and research the giant sequoias to better understand how they will react to our changing climate and to offer informed recommendations to evolving conservation strategies.

Below is a short video by The Redwoods and Climate Change Initiative (RCCI) on the impact of extended drought on Giant Sequoias. Oh, and in case you were wondering, Giant Sequoias (sequoiadendron giganteum) and Coastal Redwoods (sequoia sempervirens) are closely related, but are two different species.

Air Quality Concerns in Sequoia National Park

Situated high is California’s Sierra Nevada Mountains, Sequoia National Park protects the only place on Earth where giant sequoias – the world’s largest trees by volume – grow naturally. Air pollution, however, does not recognize the boundaries set up by the National Park Service (NPS). While hiking there recently, I learned more about the air quality issues facing this national natural treasure.

According to a recent report by the National Parks Conservation Association, Sequoia National Park received an “F” for air quality. While other parks in the NPS system also have air quality concerns, Sequoia NP was rated the worst in the nation. In 2014, its Ash Mountain monitoring station recorded 56 days where the level of ozone was above federal health standards.

In most parts of the country, air quality issues are often connected to emissions from coal-fired power plants, but in California there are a few other factors at play. While the region’s notorious wildfires do create some air quality problems, the NPS says the vast majority of the pollution in the park comes from human activities outside its borders. With a prevailing westerly wind in the region during the summer months, emissions from large-scale industrial and agricultural activities as well as massive amounts of vehicle exhaust are swept eastward from San Francisco and across the San Joaquin Valley. Trapped by the topography of the valley, the polluted air is heated and forced to rise up to the elevation of the park. Pollutants found in the air include nitrogen oxides, ground level ozone, fine particulate matter, and traces of pesticides.

Of these pollutants, ground level ozone, which forms when nitrogen oxides react with heat and U.V. light, poses the most serious threat to human health. It is known to cause a variety of repository problems and is often the reason given for air quality alerts.  It is also harmful to plants and trees – the organisms that are supposed to be protected by the park.

While ozone does not seem to be impacting mature sequoias, the NPS says experiments have shown that it is stunting the growth of sequoia seedlings. That said, other trees in the park, such as Ponderosa and Jeffrey Pines are feeling its full effect. Damaging their stomata – tiny pores on their needles that usually absorb carbon dioxide -the pollutant reduces a tree’s ability to perform photosynthesis and therefore its ability to produce and store food.  As a result, they are weakened and more susceptible to disease and insects. The telltale sign of ozone damage is the yellowing and thinning of a conifer’s needles.

Air pollution is also responsible for the smog that obscures views in the park. On a clear day, according the NPS, the view from Beetle Rock – which is about 6,200 feet above sea level – extends for more than 100 miles. In summer, when the smog is worst, that view is often significantly reduced.

The good news is that air quality issues in the park – like much of the rest of the country – have improved in recent years as a result of measures associated with the Clean Air Act. The bad news is that it still remains a serious problem. Seeing that our actions can make a difference, we can continue to reduce air pollution by conserving energy and reducing emissions – a similar strategy to reducing the impacts of climate change.

View from the edge of Giant Forest. Credit: NPS

A view looking southwest from the edge of Giant Forest in Sequoia National Park. Credit: NPS

Pyrocumulus Cloud Forms Over Wildfire in Kings Canyon National Park

Fueled by drought, wildfires have been blazing across the American West all summer.   Sixteen are currently burning in California alone. While hiking in Kings Canyon National Park in the state’s rugged Sierra Nevada Mountains recently, I crossed paths with the “Rough Fire” and saw it produce a billowing pyrocumulus cloud.

Pyrocumulus clouds form when intense heat at the surface – usually from a wildfire or volcanic eruption – causes air to rise rapidly. As it travels upward, water vapor in the air condenses into droplets and forms a cloud. Filled with ash and smoke, the swelling cloud generally appears more grey than white.

Ignited by lightning over three weeks ago, the Rough Fire continues to spread and has even caused parts of Kings Canyon National Park to close. According to the NPS, smoke from the massive fire has also impacted the air quality in and around the park. To date, the fire has charred close to 50,000 acres and is only 17% contained.

Pyrocumulus cloud rising over California's Rough Fire in Sierra National Forest and Kings Canyon National Park. August 2015. Credit: The Weather Gamut.

Pyrocumulus cloud rising over California’s Rough Fire in Sierra National Forest and Kings Canyon National Park, August 2015. Credit: The Weather Gamut.

Climate Change in Saguaro National Park

The saguaro – the classic symbol of the American southwest – is the largest cactus species in the United States and only grows in the Sonoran Desert. Straddling the city of Tucson, AZ, Saguaro National Park protects over 90,000 acres of its namesake cactus. While visiting there recently, I learned how this unique environment is being impacted by climate change.

The Southwest is the hottest and driest part of this country and climate change is making it even more so.  According to the US National Climate Assessment, 2001 through 2010 was the region’s warmest decade on record with temperatures almost 2°F above historic averages. Looking ahead, the report projects continued increases in average annual temperature and a decrease in precipitation, especially in the southernmost part of the region. In a National Park Service (NPS) report on arid lands, the agency says it has already observed a widespread winter and spring warming trend and a lengthening of the frost-free season in the Sonoran Desert.

These warmer conditions are causing a variety of environmental changes in Saguaro National Park. While fewer cacti are dying from severe freeze events, evaporation rates are increasing, making an already parched area even drier. “Arid ecosystems,” the NPS says, “are particularly sensitive to climate change and climate variability because organisms in these regions live near their physiological limits for water and temperature stress.” Even slight changes in the environment can dramatically alter the distribution and abundance of many desert species. On average, the region currently receives less than 12 inches of rain per year.

The phenology, or the timing of natural events, is also being thrown out of sync as the climate changes. The vital rains of the region’s monsoon season traditionally begin in early July, but are projected to arrive later and later in the coming years. This can be a problem for the saguaros, because they have evolved to produce fruit in the beginning of July. While adapted for the dry desert environment, the cacti still depend on adequate rain during the summer growing season for both their own survival and the establishment of seedlings.

Another serious climate change challenge for the Sonoran Desert is the spread of non-native plant species. Buffelgrass, a native of Africa, was introduced to Arizona in the 1940’s for cattle forage. Thriving in the heat, this invasive species is crowding out the native plants (including the cacti), changing the look of the landscape, and increasing the risk of wildfires.

The Sonoran Desert did not evolve with fire as an ecological factor. Lush with vegetation by desert standards, the region usually had large gaps between groups of plants. This helped keep any wildfires small. Now, as the buffelgrass fills in those open spaces, fires can burn hotter and spread much more easily. Adding insult to injury, the buffelgrass grows back after a fire has killed the native plants.

The changing environment is also problematic for the animals that depend on the saguaros for food and shelter. These include a wide array of species, ranging from woodpeckers to coyotes.

Scientists are continuing to monitor and research how additional changes in temperature and precipitation will affect this beautiful and unique place.

Saguaro National Park, Arizona.  Photo Credit: The Weather Gamut

Saguaro National Park, Arizona.  Photo Credit: The Weather Gamut

Climate Change at Rocky Mountain National Park

Rocky Mountain National Park (RMNP) protects 415 square miles of spectacular mountain environments in northern Colorado. It is home to a diversity of ecosystems – alpine, subalpine, and montane – that are each uniquely adapted to the climate zone of their elevation. This is why, as I learned during a recent visit,  climate change is a serious issue for the park.

According to the National Park Service, the average annual temperature in RMNP has increased 3.4°F over the past century. A report from a weather station inside the park (Grand Lake), shows that the number of frost-free days has increased from an average of 65 in the mid-20th century to an average of 100 in this past decade.


In the 20th century, the area including Rocky Mountain National Park experienced a warming trend. The five-year rolling average (thick red line) allows the viewer to look beyond annual variability to focus on long-term trends. (Analysis of PRISM data, original source Daly 2008). Credit: NPS

This warming trend, says the NPS, has caused a number of environmental changes in RMNP. The winter snowpack is melting approximately 2 to 3 weeks earlier, resulting in less water being available for people, plants, and animals during the summer. There has been an explosive increase in the number of mountain pine beetles surviving the now warmer winter months, allowing them to devour more trees. The phenology, or the timing of natural events, can also be thrown out of sync when warm spring weather arrives earlier than normal. Wildflowers that bloom before the arrival of butterflies, for example, can leave the insects with a reduced food source. This puts a kink in how the larger food chain fits together.

In the park’s alpine tundra region, the American Pika is at particular risk. According to scientists, this small furry relative of the rabbit can only live at high elevations in cool, rocky environments. They say it cannot survive in temperatures above 75°F for more than a few hours.  While other species adapted to lower elevations can move upslope as average temperatures rise, the pika has nowhere to go.

American Pika on the rocky terrain of RMNP's alpine tundra region.  Image Credit: The Weather Gamut.

The American Pika, a native of RMNP, is sensitive to even small changes in climate.  Image Credit: The Weather Gamut.

Another impact of climate change is the spreading of non-native plant species that can thrive in the now warmer environment of RMNP. While Cheatgrass, a native of Eurasia, is found throughout the western US, it used to be limited to lower elevations.  Now, it is found as high as 9,500 feet in parts of RMNP. In addition to crowding out native plants and changing the look of the landscape, this invasive species is highly flammable. Its presence increases the danger of wildfires – something the West certainly does not need.

While these are just a few examples of the observed and expected impacts climate change is and will have on RMNP, scientists are continuing to research how additional increases in temperature will affect this national treasure.

Why Air Temperature Decreases with Height

While visiting Colorado recently, I had the opportunity to explore Rocky Mountain National Park, and it was largely a vertical experience. Within its borders are 72 named peaks that reach above 12,000 feet in elevation. Traveling from the Beaver Meadow Visitor Center – elevation 7,840 feet – to the Alpine Visitor Center – elevation 11,796 feet – the drop in temperature was anything but subtle.

The reason for air being cooler at higher elevations is twofold. First, the sun’s rays heat the Earth’s surface, which in turn, radiates that warmth into the atmosphere. As you climb in altitude, there is less surface area of land available to heat the air. Second, as air rises, it expands and cools. This is because air density and pressure aloft are lower than at the surface.

The exact rate at which the temperature decreases with height – the environmental lapse rate – varies with location and daily conditions. On average, however, for every 1000 feet gained in elevation, the temperature drops by about 3.6°F.

Image Credit:British Geographer

Image Credit: The British Geographer