Bryce Canyon Landforms
Bryce Canyon National Park is located in the High Plateaus region of the Colorado Plateau in Utah. Elevation, climate, rock type and the plateau's orientation are elements that, when combined, form unusual shapes called hoodoos. No where else in the world can one find a concentration of pinnacles with odd shapes like those found in Bryce Canyon.
Most visitors come to Bryce Canyon National Park by way of other National Parks on the Colorado Plateau such as Arches, Canyonlands, Natural Bridges, Capitol Reef and Bryce Canyon. Each park attracts visitors for different reasons.
The Virgin River cuts down through resistant sandstone forming the deep canyon of Bryce Canyon National Park. Gravity defying arches of Arches National Park form in resistant sandstone by frost wedging and water erosion in fractures. Continuous down cutting by the Colorado River forms deep incised meanders in sandstone layers at Canyonlands National Park.
Bridges form in sandstone by river action eroding into fins at Natural Bridges National Monument. Capitol Reef National Park was formed by water erosion that exposed vibrant rock layers folded into a monocline by an ancient fault. All the parks mentioned contain massive structures, which tower over awed spectators. It seems inconceivable that anything other than the strong erosive force of water could have carved and exposed these immense landforms.
Visitors at Bryce Canyon National Park come to see the unique shapes formed in the Claron Formation. Bulbous, wavy spires and fins protrude from the plateau's sides like the veins on plant leaves. These are commonly known as Hoodoos. The mystical shapes inspire imagination and intrigue.
It appears impossible that the destructive forces of water carved these fragile landforms. Instead many believe the hoodoos of Bryce Canyon were formed by wind. This is a mistaken idea. Wind is an effective form of erosion for many locations. However, for Bryce Canyon wind has little effect on the creation and destruction of the various shapes.
Hoodoos formed over thousands of years by the same processes that form the features of surrounding parks. Water, ice (at varying intervals) and gravity are the forces that form Bryce Canyon. These three erosive forces coupled with the differential erosion of the four rock types of the Claron Formation produced a different morphology than that of other parks. 10-15 million years ago the Paunsaugunt Plateau was caught and uplifted by the Colorado Plateau. Breaks called joints formed in the plateau during the uplift. Joints allowed water to flow into the rock. As water flowed through joints erosion widened them into rivulets and gullies. Over time, deep slot canyons formed in the sides of the plateau.
Bryce Canyon receives an average rainfall of 10 inches a year in the valley and approximately 19 inches a year on the plateau. Majority of the precipitation falls in mid to late summer. It comes in the form of monsoons, usually in the afternoon. These thunderstorms can be fierce, dropping an inch or two of rain in under an hour. Hail storms often accompany heavy rains in the region. Most of the rainfall is not absorb by the thin layer of soil covering the rocks. Because soils at Bryce Canyon are very dry, much of the water runs off the surface. Only the top inch, or so,of soil absorbs rainfall before it starts to run off. When this happens at Bryce Canyon flash floods are the result.
At Bryce Canyon water in the form of ice is the most efficient form of erosion for breaking rock into smaller pieces. The Paunsaugunt Plateau receives approximately 100 inches of snowfall a year. It also experiences about 200 days of freeze/ thaw. Which means that everyday a small amount of snow melts and runs into the joints and freezes at night. When water freezes it expands to form an ice wedge in the joint widening the space. As the ice wedge grows by more water leaking into the joint and freezing it will finally break the rock. This is called frost wedging.
Small pebbles and large Volkswagen bus sized boulders commonly fall from the sides of existing hoodoos and the sides of the Paunsaugunt Plateau by frost wedging and gravity. The smaller pieces are washed away by the monsoons and snow melt. Boulders explode into cobble sized pieces when they impact the ground. The resulting debris is washed down slope by snowmelt, flashfloods and gravity. Rock type is another factor in the creation of the bizarre shapes of hoodoos. The hoodoos at Bryce Canyon are carved in the Claron Formation. Limestone, siltstone,dolomite and mudstonemake up the four different rock types that form the Claron Formation. Each rock type erodes at different rates. The rock's resistance to erosion is what causes the undulating shapes of the hoodoos.
Dolomite, limestone and siltstone are very hard and form the protective caprock on most of the spires. Frost wedging is the erosional force that breaks apart the harder rocks. Mudstone is the softest rock in a hoodoo and is easily identified because it forms the narrowest portion of the pinnacles. As mudstone moistens it erodes easily and will run down the sides forming a stucco or protective coating. Every time it rains the stucco is renewed.
Eolian or wind forces erode at slow rates. If wind does not erode the stucco layer fast enough it will renew before eolian erosion affects the rock. For this reason wind has little to no affect on hoodoo formation or destruction.
Another sign that wind is not responsible for hoodoo formation is the absence of a dominant wind direction pattern carved into the plateau. If eolian forces were responsible for erosion in the area hoodoos would erode parallel with the prevailing wind direction.
At Bryce Canyon National Park hoodoos do not align with the prevailing air currents. Hoodoos protrude from the sides of the plateau in lines that follow joint patterns caused by faults that uplifted the area. Some of the walls and fins meet at almost a 90-degree angle. Wind erosion would not form patterns like this. (Below is a photo showing fins in a linear patterns extending from the plateau).
After a heavy rain, soil in the region dries out and forms a hard crust. Wind erosion requires loose particles to be transported with in the air column and impacted into a surface for erosion to take place. The particles need to be free and not attached to a crust. Because of the crust there is not a large supply of loose particles to be used for wind erosion in the area. Vegetation also keeps loose grains in place by their roots and by slowing the gusts of wind as it blows through the branches.
Erosional scours paralleling the hillslopes are carved on the slot canyon walls. They are common in many places within the park.
As hikers descend into Wall Street on the Navajo Loop a close inspectionof the canyon walls will show diagonal erosive marks cutting through horizontal bedding planes. (The photos show show horizontal bedding planes and the diagnol scour marks.) These scour marks show the erosion point of historical hillslopes. If wind erosion were responsible for the formation of walls, fins and hoodoos the old scour marks would have been eroded away along with the hillslope.
Hoodoo surfaces would be smoother and more round if wind erosion were responsible for their creation. Instead many hoodoos have sharp edges and jagged tops like the skyline of 'The Silent City'. Angular pinnacles, stuccoed sides, boxy erosional patterns and scour marks are some of the more obvious tells of water erosion.
While visiting Bryce Canyon National Park look for signs of wind and water erosion. It is suprizing how visible the numerous signs of water erosion are, when you know what to look for.
Our dynamic planet is constantly being shaped and reshaped by dramatic events such as earthquakes, volcanoes, and mudslides. Other changes may not be detected in a human lifetime. Geological timespans or Periods cover millions of years. The Cretaceous Period began some 144 million years ago and lasted until about 63 million years ago. The rock formations you see exposed at Bryce Canyon began to develop during this time. For 60 million years a great seaway extended northwestward into this area, depositing sediments of varying thickness and composition as it repeatedly invaded, retreated, then re-invaded the region. Retreating to the southeast, it left sediments thousands of feet thick. Their remnants form the oldest, lowest, gray-brown rocks at Bryce Canyon.
In the Tertiary Period, between 66 and 40 million years ago, highlands to the west eroded into shallow, broad basins. Iron-rich, limy sediments were deposited in the beds of a series of lakes and streams. These became the reddish rocks of the Claron Formation from which the hoodoos are carved and for which the Pink Cliffs are named.
The Cretaceous Seaway moved northward from the Gulf of Mexico into this region of North America (left). Sediments deposited as the sea invaded and retreated became the brown and gray marine rocks now exposed at the park's lowest elevations and across the Paria Valley.
Deformation, Uplift, and the Grand Staircase
Horizontal compression related to the formation of the Rocky Mountains deformed these rocks. Then volcanic flows from the north covered parts of the region: black rocks at the mouth of nearby Red Canyon and on the Sevier Plateau to the north still protect softer underlying layers. About 10 million years ago the Earth pulled apart, moving and tilting great blocks along north-south trending fault lines. Layers, once connected, were displaced vertically by several thousand feet, forming the High Plateaus of Utah.
Older Cretaceous layers rested side by side with younger Tertiary layers across fault lines. Streams began to remove sediments deposited by their ancestors. Working on the weakened edges of the upthrown blocks, water gradually removed the uppermost Tertiary layers and exposed Cretaceous rocks once again. Now these drab former marine sediments lay on the surface of the land side by side with the brightly colored deposits of freshwater lakes and streams.
Water erodes rock mechanically and chemically. Scouring, abrading, and gullying occur when fast-moving water scrapes its silt, gravel, and rock debris against firmer bedrock. Slow-moving or standing water enters minute rock pores and dissolves cements holding the rock together. This leaves loose grains to wash away. Softer Cretaceous rocks were loosened and carried away from the upthrown block by the Paria River. The resulting Paria Valley is carved out of rocks that lie deep beneath the Paunsaugunt Plateau, whose edge now is exposed to erosion.
Along the plateau rim, conditions are optimal for erosion. Its steep slope increases water speed and energy. Faults and joints from ancient compressional forces influence erosion patterns. Freezing and thawing loosen slope surfaces. Debris carried by runoff, scours softer rock and creates gullies; harder rock remains as fins.
As gullies widen to canyons, fins (left) become exposed to further erosion along vertical cracks. In winter, freezing water expands within cracks to peel off layers and carve vertical columns (right).
Hoodoos Cast Their Spell
Hoodoo - a pillar of rock, usually of fantastic shape, left by erosion. Hoodoo - to cast a spell. At Bryce Canyon National Park erosion forms a remarkable array of fantastic shapes we know as hoodoos. Surrounded by the beauty of southern Utah, these hoodoos cast their spell on all who visit. Geologists say that ten million years ago forces within the Earth created and then moved the massive blocks we know as the Aquarius and Paunsaugunt plateaus. Rock layers on the Aquarius now tower 2,000 feet above the same layers on the Paunsaugunt. Ancient rivers carved the tops and exposed edges of these blocks, removing some layers and sculpting intricate formations in others. The Paria Valley was created and later widened between the plateaus.
The Paria River and its many tributaries continue to carve the plateau edges. Rushing waters carrying dirt and gravel gully the edges and steep slopes of the Paunsaugunt Plateau on which Bryce Canyon National Park lies. With time, tall thin ridges called fins emerge. Fins further erode into pinnacles and spires called hoodoos. These in turn weaken and fall, adding their bright colors to the hills below.
Early Native Americans left little to tell us of their use of the plateaus. We know that people have been in the Colorado Plateau region for about 12,000 years, but only random fragments of worked stone tell of their presence near Bryce Canyon. Artifacts tell a more detailed story of use at lower elevations beyond the park's boundary. Both Anasazi and Fremont influences are found near the park. The people of each culture left bits of a puzzle to be pieced together by present and future archaeologists. Paiutes lived in the region when Euro-Americans arrived in southern Utah. Paiutes explained the colorful hoodoos as "Legend People" who were turned to stone by Coyote.
The Paiutes were living throughout the area when Capt. Clarence E. Dutton explored here with John Wesley Powell in the 1870s. Many of today's place names come from this time. Dutton's report gave the name Pink Cliffs to the Claron Formation. Other names — Paunsaugunt, place or home of the beavers; Paria, muddy water or elk water; Panguitch, water or fish; and Yovimpa, point of pines— were derived from the Paiute language.
The Paiutes were displaced by emissaries of the LDS Church who developed the many small communities throughout Utah. Ebenezer Bryce aided in the settlement of southwestern Utah and northern Arizona. In 1875 he came to the Paria Valley to live and harvest timber from the plateau. Neighbors called the canyon behind his home Bryce's Canyon. Today it remains the name not only of one canyon but also of a national park.
Shortly after 1900, visitors were coming to see the colorful geologic sights, and the first accommodations were built along the Paunsaugunt Plateau rim above Bryce's Canyon. By 1920 efforts were started to set aside these scenic wonders. In 1923 President Warren G. Harding proclaimed part of the area as Bryce Canyon National Monument under the Powell (now Dixie) National Forest. In 1924 legislation was passed to establish the area as Utah National Park, but the provisions of this legislation were not met until 1928. Legislation was passed that year to change the name of the new park to Bryce Canyon National Park.
Each year the park is visited by more than 1.5 million visitors from all over the world. Languages as varied as the shapes and colors of the hoodoos express pleasure in the sights. Open all year, the park offers recreational opportunities in each season. Hiking, sightseeing, and photography are the most popular summer activities. Spring and fall months offer greater solitude. In the winter months, quiet combines with the area's best air quality for unparalleled views and serenity beyond compare. In all seasons fantastic shapes cast their spell to remind us of what we protect here in Bryce Canyon National Park.
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