Geology and Ecology of National Parks

Denali National Park and Preserve

Mountain View, Denali National Park

Denali National Park and Preserve view of the mountain.

(Credit: Trent Caswell.)

Denali National Park and Preserve spans over 6 million acres in the heart of Alaska where spectacular mountains and glaciers encompass a remote sub-arctic wilderness.  A majority of the land requires travel either by aircraft or on foot and there is only one road entering and exiting the park. Anchorage is the closest major city located 137 miles to the south. In 1917, the wilderness area became the first national park created specifically to protect wildlife, and then became a designated international biosphere reserve in 1976.  Denali National Park and Preserve became its official name in 1980 to honor Denali Mountain, the highest point of North America.

Southwest view of Denali Peak above Kahiltna Glacier

Southwest view of Denali Peak above Kahiltna Glacier.

(Credit: Dee Williams , USGS. Public domain.)

Denali is well known for its elevation reaching 20,310 ft., but many people are unaware that Denali is actually a full mile taller than Mt. Everest. A mountains’ height is measured from base to summit. Denali measures around 18,000 ft from base to summit, while Mount Everest is around 5,000 ft less. This is possible because Mount Everest is the highest mountain on earth, but not the tallest. While Denali is technically taller, the base starts out at a lower elevation than Everest, reducing the overall height it can reach. Specifically, Denali’s base is located a mere 2,000 ft above sea level while Everest's base begins at 14,000 ft above sea level. So, while Everest reaches the highest point in the atmosphere, the distance from base to peak of Denali constitutes a greater vertical rise.

The name Denali derives from the Koyukon Alaska Native language, which translates to “Tall one”. Alaska has a rich Native American history and many other Athabascan tribes also had their own unique names for the mountain. The park and mountain experienced a recent name change from Mt. McKinley in 2015 under President Barack Obama. The mountain was dubbed McKinley at the start of the Alaskan gold rush to honor the (not yet elected) President McKinley. Despite the publicity he received from the naming of the mountain, President McKinley never once visited the state nor the mountain that bore his name. This, along with the close ties of the mountain to the Alaska Native community, was one of the principal arguments for returning it to the original name.

Geology

Denali’s elevation is a product of processes called plate tectonics. Tectonic plates on Earth’s surface essentially float on the underlying mantle. The mantle is partially molten and can move the plates on top of it due to convection currents within the mantle. In Alaska, these currents cause the tectonic plates referred to as the Pacific Plate and Yakutat microplate to move northward. As these plates have moved northward, they have collided with the stable North America Plate and, in this case, cause a mountain building period referred to as an orogeny.

Image: Denali Fault

(Credit: Peter Haeussler, U.S. Geological Survey. Public domain.)

The upward growth of a mountain is referred to as uplift. Mt. Denali is a part of the Alaska Range and the uplift of the range as a whole started during the Cenozoic era. The uplift of Denali National Park and Preserve is caused by the collision of tectonic plates as well as its location along a prominent fault. A geological fault is where significant amounts of rock have been displaced, and there is such a fault (aptly named the Denali fault) that has a bend where Denali is situated. This bend causes the rocks to stack on top of one another and increase the mountain's height. The fault itself runs almost 1,200 km long from the Yukon border all the way to the Bering sea. The Denali fault crosses most of Alaska’s width and is considered active, causing the height of Denali to increase by about .5 mm per year. There are many smaller faults throughout the park and preserve.

Denali mountain is composed primarily of igneous rocks crystallized from magma and metamorphic rocks. Metamorphic rocks are rocks that were changed or altered from their original state into something new, due to intense amounts of heat or pressure. Four particularly evident types of metamorphic rock in Denali are slate, marble, quartzite, and schist. The Pacific plate is an oceanic plate, and the North American plate on which Alaska sits is a continental plate. Oceanic plates are significantly denser than continental plates, so when they collide the lighter continental plate is lifted up as the oceanic plate slides under it.

Image: Denali Fault: Canwell Glacier

Denali fault, Canwell Glacier.

(Credit: Peter Haeussler, U.S. Geological Survey. Public domain.)

Much of Alaska is composed of accreted terranes, a phrase which refers to fragments of other continents, ocean basins, and islands that collide and attach themselves to a new continent. The two major terranes are the Yukon-Tanana terrane which collided with Alaska around 225 million years ago, and the Talkeetna Superterrane which collided with Alaska 110 to 85 million years ago.  There are other smaller terranes in Denali National Park and Preserve but these two make underlie the majority of the park's landforms. The collisions where accreted terranes are attached happens very slowly. In fact, the most recent collision of the Yakutat terrane with southern Alaska began around 30 million years ago and is still underway.

Much of Denali’s landscape was forged by glaciers and the resulting meltwater. Glacial melt refers to glacier water runoff that serves as a mechanism of erosion, wearing away rock and sediment over time. A very powerful form of erosion is the glacier itself, forming at the highest elevation where ice and snow won't melt due to the low temperatures.  Eventually the glacier moves downhill under the force of gravity and its own immense weight. Movement of glaciers can carve valleys, ridges and other rock features and even form lakes if melted. These traveling glaciers can be so powerful that they may pick up large boulders and carry them downhill, depositing rocks in completely foreign terrain, often with completely different composition.

Denali mountain is known to be one of the coldest in the world. This is due to its high elevation and extreme northern location, which is much farther north than Mt. Everest. Denali National Park and Preserve contains over 400 glaciers, with the most well-known being the Kahiltna Glacier and the Ruth Glacier. Kahiltna Glacier is by far the longest glacier in the park at 44 miles long, while Ruth glacier is the thickest. The presence of the glaciers are supported by the high latitude of the park, elevation of the mountain, and the permanent snowpack above 7,000 ft elevation. The majority of Denali’s glaciation occurred during 4 widespread glaciation periods that encompassed much of North America in the past 3 million years.

Glaciers used to cover far more of Denali’s landscape but are slowly disappearing due to a warming planet. In fact, Alaska has warmed more than twice the rate of the rest of the United States.

 

Geology of Denali National Park and Preserve by Time Period

Precambrian: 4,600 million years - 541 million years ago

The oldest rocks in Denali National Park and Preserve originate from the late Precambrian and early Paleozoic era, and are found on the Yukon-Tanana terrane. These geologic units are metamorphic rocks such as schist, amphibolite, greenstone, and quartzite. These rocks were formed and then deformed by metamorphism in an ancient ocean basin when North America was still part of the supercontinent Rodinia.

 

Paleozoic: 541 million years - 251.9 million years ago

The Paleozoic was the start of volcanic activity in Denali and coincided with the breakup of the supercontinent. Layers containing mud, sand, marine life, and volcanic ash were deposited during this period and later deformed by extensive metamorphism. These limey mud layers were later metamorphosed into marble.

Ordovician: Common rocks in Denali National Park from the Ordovician period are chert, slate, greenstone, limestone, and dolostone.

Devonian: During the Devonian period, the area was an island arc (a chain of volcanic islands) which made limestone, lava flows, and volcanic ash dominant rock types.

Carboniferous-Permian: Due to the area being marine during this time period, the most common rocks are limestone, mudstone, and sandstone.

 

Mesozoic: 251.9 million years - 66 million years ago

The Mesozoic was a period of intense mountain building (orogeny), which led to many accreted terranes on the western edge of the continent. This led to deformation of the existing ocean basin. The Mesozoic encompasses the Triassic, Jurassic, and Cretaceous periods.

Triassic: Volcanic hotspot activity is evident from the remaining greenstone, tuffs, and basalt lava flows.

Jurassic-Cretaceous: The Jurassic and Cretaceous periods were dominated by formations of sandstone, argillite, conglomerates, limestones, and a large variety of other rock types. This represents widespread plate tectonic activity. The orogeny that led to the formation of the ancestral Alaska Range began in the Cretaceous period.

 

Cenozoic: 66 million years ago- present day

These time periods led to formations of large amounts of rhyolite, andesite, granite, and other intrusive igneous rocks at depth and sandstone and mudstone at the surface.

Tertiary: During the Tertiary period there was extensive faulting that created large basins that collected sediment. These basins led to the formation of many coal seams and swamp environments.

Quaternary: As recently as 6 million years ago, the rapid uplift of the Alaska Range was still underway. At the same time this uplift occurred, several ice age cycles occurred as well, contributing to glacial formations and diversion of major streams and rivers to flow north. Following these ice age cycles, the first vegetation and coniferous forests took root. Evidence of them can be found in many organic deposits in the park.

 

Notable Formations:

Wickersham Wall

One of the most well-known geological formations in Denali National Park and Preserve is the Wickersham Wall, which contains one of the highest continuous mountain faces in the world. Glaciers off of Wickersham wall can reach lengths of up to 45 miles long.

Kantishna Hills

The Kantishna Hills of Denali National Park and Preserve are composed of metamorphic rocks from the Precambrian to Paleozoic era, and contain geological features called dikes dating back to the Cretaceous period. Dikes are slabs or sheets of rock that form in fractures of pre-existing rock beds. One of the most interesting geological features of the Kantishna Hills is the Kantishna Hills Anticline, which is underlain by a cluster of recent earthquakes and is actively deflecting river courses. An anticline is where rock beds have been folded into an arch by tectonic activity, with the oldest rock beds at the center of the arch.

Polychrome Overlook

Polychrome overlook is a popular stop on the one road winding through Denali, notable for its multi-colored rock and sediment caused by the volcanism. Volcanism was active in the park as recently as 38 million years ago, though these rocks formed closer to 56 million years ago. The rocks are composed of rhyolite tuffs, layered with other volcanic flows.

Wonder Lake, Denali National Park

Wonder Lake. 

(Courtesy: Trent Caswell)

Wonder Lake

Wonder lake is a kettle lake and reaches a depth of 268 feet. A kettle lake is a lake the forms in depressions left by receding ice blocks that fill with water. There are many opportunities for viewing waterfowl as this region of Denali tends to be wetter than other areas in the park. It is also a popular camping and hiking destination.

Eielson Visitor Center

Eielson Visitor Center is open only during summer but is well known for being near some of the best Denali views. From the visitor center you can see evidence of some of the parks most recent volcanism which formed Mt Galen. Mt Galen is primarily composed of basalt, dacite, rhyolite, and andesite lava formations.

Image: Teklanika Campground Sign

Sign for Teklanika campground at Denali National Park.

(Public domain.)

Teklanika Campground

Visiting Teklanika Campground, you would be standing atop what is called the Cantwell Formation. The Cantwell Formation is significantly younger than the rocks below it, meaning that there is a gap in the time record referred to by geologists as an unconformity. The gap in time amounts to somewhere between 65-100 million years of “missing time”.

 

Forget Me Not

Alpine Forget-me-not is the Alaska State Flower.

(Courtesy: Trent Caswell)

 

 

 

 

 

 

Ecology 

All of the geologic evolution discussed above has, in turn, affected what kinds of plants and animals are able to thrive in the park. Within Denali National Park and Preserve there are known to be two major climates, one on either side of the Alaskan Range. North of the range, winters are known to be very long and very cold as that climate is greatly affected by Arctic pressure systems. This also leads to very low precipitation. As a result, certain vegetation is more suitable to the south than the north, such as spruce trees which grow in greater numbers north of the range and also grow over permafrost. These conditions are subalpine and alpine in elevation, so scrub vegetation and spruce trees are the dominant vegetation. While many people do not think of wildfires occurring in such a cold area, wildfires from lightning storms are common north of the range. Due to the frequent fires clearing trees, a majority of the Spruce are less than 120 years old. The most common shrubs north of the range where it is drier are grasses, sage brush, juniper, and other herbaceous perennials. The very tops of the high alpine segment of the park are unvegetated and composed only of bare rock. The upper limit of plant growth is about 7,500 ft and the growth above this point is typically only small lichens.

 

 

 

 

 

 

 

Denali National Park & Preserve- Bell Heather

Denali National Park & Preserve- Bell Heather

(Courtesy: Trent Caswell)

 

 

South of the Alaska Range there is less permafrost than north of the range, and the snowfall is very high. This climate is more suitable to lush vegetation than the harsh north. The forests here have greater variety in species and are much denser, less scattered forests. There are also many lowlands within the park that are dominated by black spruce, white spruce, and birch forests that became fully established after the last glacial period. Rivers and warmer south facing slopes can sometimes support herbs, aspen, and poplar. Other shrubs in the area include willow, blueberry, dwarf birch, rose, grasses, lupine, cow parsnip, bell heather, and brush cranberry.

 

 

 

 

 

 

 

 

 

 

 

Grey Wolf

Denali is famous for its wolves- depicted here is a Grey Wolf spotted near the main entrance of the park.

(Courtesy: Trent Caswell)

Wildlife

There is abundant wildlife to be found in Denali National Park & Preserve, including bears, caribous, wolves, moose, and Dall sheep. Smaller animals coexist within the park as well, in fact the dark has 39 different species of mammal.  Caribou within the park travels as a heard as is currently the largest heard in North America that is not allowed to be hunted (provided they remain within the parks bounds). The parks wolves are some of the most studied animals within the park and the park is known for being one of the best places in the world to view wolves in the wild.

 

 

 

 

 

 

 

 

 

Human Settlement

The two primary settlements nearest Denali National Park & Preserve are Nenana Canyon and Talkeetna. Talkeetna is a railroad town whose name means “where rivers join” in the Athabascan language. It is also the base camp for climbers looking to summit Denali, taking a plane to the nearby Kahiltna Glacier before starting their trek. Nenana Canyon is on the opposite side of Denali and known for having a great variety of hotels, shopping, and rafting companies.

Map of Denali National Park and Preserve

Map of Denali National Park and Preserve 

(NPS, Public domain.)