Glacier Bay Basin in southeastern Alaska, in the United States, encompasses the Glacier Bay and surrounding mountains and glaciers, which was first proclaimed a U.S. National Monument on February 25, 1925, and which was later, on December 2, 1980, enlarged and designated as the Glacier Bay National Park and Preserve under the Alaska National Interest Lands Conservation Till or glacial till is unsorted glacial sediment.. Till is derived from the erosion and entrainment of material by the moving ice of a glacier.It is deposited some distance down-ice to form terminal, lateral, medial and ground moraines.. Till is classified into primary deposits, laid down directly by glaciers, and secondary deposits, reworked by fluvial transport and other processes. Moraines are made up of pieces of rock that are shattered by frost action, embedded in the glaciers & brought down the valley. New Exchequer Dam is the largest dam on the river and forms Lake McClure, which holds 1,032,000 acre-feet (1.273109m3) of water for irrigation, flood control and hydropower generation. The Lake McClure gauge, located at the former mining town of Bagby, is probably the most accurate gauge for flows overall. The immense lateral moraine that was formed in the process is clearly visible from the moraine trail. It is strongly characterised and divided into different areas by end moraines, various glacial snouts and medial moraines. National Hydrography Dataset high-resolution flowline data. Other types of moraine include ground moraines (till-covered areas forming sheets on flat or irregular topography) and medial moraines (moraines formed where two glaciers meet). This glossary of geography terms is a list of definitions of terms and concepts used in geography and related fields, including Earth science, oceanography, cartography, and human geography, as well as those describing spatial dimension, topographical features, natural resources, and the collection, analysis, and visualization of geographic data.. Related terms may be found in Since 1980 numerous small glacial lakes formed behind the new terminal moraines of several of these glaciers. [40] Below this dam is Merced Falls Dam, an irrigation diversion dam. [14], Many species of plants are found throughout the middle and upper basin, including California poppy, white alder, Oregon ash, oak, poison oak, bigleaf maple, Indian rhubarb, buttonbush, willow, whiteleaf manzanita, and historically, sugar pine, before heavy logging in the late 19th century. After the Tioga Glacier retreated this moraine formed a lake that flooded nearly the entire valley. [29] Some towns that followed were Hopeton, Snelling and Merced Falls, the latter named for a set of rapids on the Merced River near the present-day site of McSwain Dam. In addition, the river is fed by dozens of high Sierra lakes, the largest of which include Merced Lake, Tenaya Lake, Ostrander Lake, the Chain Lakes, and May Lake. Whitewater rafting is permitted throughout Merced River Canyon from the downstream half of Yosemite Valley to the entrance of Lake McClure. The work of the glacier then left an overdeepened U-shaped valley that ends abruptly at a valley or trough end. moraines and erratics. Many other trails lead throughout the Merced River watershed, notably the John Muir Trail, which starts near Happy Isles and climbs the Giant Staircase, past Vernal and Nevada Falls, into Little Yosemite Valley and north along Sunrise Creek to join the Pacific Crest Trail near Tuolumne Meadows. Moraines. Birds that occur commonly in the middle and upper sections of the Merced River include mourning dove, Cassin's finch, California quail, dark-eyed junco, woodpecker, dipper, great blue heron, scrub jay, red-winged blackbird, red-tailed hawk, turkey vulture, cliff swallow, canyon wren, merganser, and bald eagles. Depending ond the location of the deposits, moraines can be divided into 4 types: ground moraines, lateral moraines, medial moraines and terminal moraines. There are no trails along some segments, including the lower Bridalveil Creek, upper South Fork, and specifically Tenaya Canyon, which is extremely dangerous.[6]. These various areas of the lake have their own names. A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. Dover functioned as an "inland seaport" where boats delivered supplies from the San Francisco Bay area to settlers in the San Joaquin Valley. Gradual sedimentation filled Lake Yosemite, creating a broad and flat valley floor. A V shaped valley is formed due to the erosional work of a river. 'study of ice') is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice. Over a period of time, the amount of load in the flow starts increasing. Campgrounds along the Merced River and its tributaries include ones at Railroad Flat, McCabe Flat, Willow Placer, Merced Lake, Vogelsang Lake, Sunrise Creek, May Lake, Bridalveil Creek, and a ski hut at Ostrander Lake, the source of Bridalveil Creek. U.S. Geological Survey. Irrigation return flows carry pesticides, fertilizer and other pollutants into the river. A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. The Tioga glacier left at the mouth of Yosemite Valley a rocky moraine. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were formed at the foot, marking the maximum advance of the glacier. This modern structure was preceded by the old Exchequer Dam forming 281,000-acre-foot (347,000,000m3) Exchequer Reservoir. [8][9], The Merced River is the third largest tributary of the San Joaquin River. Moraines are made up of pieces of rock that are shattered by frost action, embedded in the glaciers & brought down the valley. Environmental measures enacted in the late 20th century have had some success in boosting chinook salmon populations, from a record low of 500 fish during several years in the 1950s, to a high of 30,000 in 1984. Despite its partial status as a National Wild and Scenic River, the Merced River has many dams and irrigation diversions. Other types of moraine include ground moraines (till-covered areas forming sheets on flat or irregular topography) and medial moraines (moraines formed where two glaciers meet). [18] Extensive layers of marine sedimentary rock that originally made up the ancient Pacific seabed were also pushed up by the rising granite, and the ancestral Merced River formed on this layer of rock. Intense pressure underground caused some of the Pacific Plate to melt, and the resulting upwelling magma pushed up and hardened into the granite batholith that makes up much of the Sierra Nevada. Sediments of glacial origin continued to travel down the Merced River following then, helping to form the flat floor of the Central Valley. moraines and erratics. Gradual sedimentation filled Lake Yosemite, creating a broad and flat valley floor. There are many activities within the watershed, including boating, fishing, camping and hiking. Fall chinook salmon travel up a fish ladder into the hatchery's pools, which are supplied with water diverted from the Merced River.[15][37]. [4][5][6] Tenaya, Yosemite, Bridalveil and Pigeon Creeks join the Merced River in Yosemite Valley. [17], When the North American Plate on its slow journey westwards encountered the Pacific Plate approximately 250 million years ago during the Paleozoic, the latter began to subduct under the North American continent. The Sierra Miwok and Mono Lake Paiute eventually, through cultural interaction over time, formed a new culture, the Ahwahnechee, derived from Ahwahnee, meaning "the valley shaped like a big mouth" (referring to U-shaped Yosemite Valley). As a whole, the system includes about 4,000 control gates and 793 miles (1,276km) of canals and laterals. The depositional landforms of glacial are described in below: A) Moraines (Fig 1): Ridges or layers of till are called moraines, they are of four types: i) ground moraines, ii) lateral moraines, iii) medial moraines, and iv) terminal moraines. An outwash plain, also called a sandur (plural: sandurs), sandr or sandar, is a plain formed of glaciofluvial deposits due to meltwater outwash at the terminus of a glacier.As it flows, the glacier grinds the underlying rock surface and carries the debris along. [27] Moraga's expedition was part of a series of exploratory ventures, funded by the Spanish government, to find suitable sites for missions in the Central Valley and the Sierra Nevada foothills. Many depositional landforms result from sediment deposited or reshaped by [12] Finally, for the gauge at Happy Isles, the largest flow ever recorded was 10,100 cubic feet per second (290m3/s) in the 1997 Yosemite floods, which destroyed many campgrounds, roads, paths, and bridges in the valley. [38][39], Downstream of New Exchequer Dam is McSwain Dam, which serves as a regulating forebay for New Exchequer Dam and also generates power. When lateral moraines adjacent to each other join, they create medial moraines, which are also carried down on the surface of the moving ice. Due to differences in climate, there is a large disparity between species found in the upper watershed (above Lake McClure) and along the lower river. The California Gold Rush brought many people into California and some settled in towns along the lower Merced River. One of these trips, headed by lieutenant Gabriel Moraga, arrived on the south bank of the Merced River on September 29, 1806. Glaciology is an interdisciplinary Earth science that integrates geophysics, geology, physical geography, geomorphology, climatology, meteorology, hydrology, biology, and ecology. Leaving Merced Lake, the river continues to the west northwest for 2.3 miles (3.7km) where the canyons open up into Echo Valley. Environmental movements led by John Muir and Robert Underwood Johnson convinced the U.S. Congress to establish Yosemite National Park in 1890. Kettles are formed when glacial retreat and melting is rapid, and blocks of ice are still buried under till. Later, when the glaciers retreated leaving behind their freight of crushed rock and sand (glacial drift), they created characteristic depositional landforms.Examples include glacial moraines, eskers, and kames. One of the first was Dover, established in 1844 at the confluence of the Merced River with the San Joaquin River. Eventually, plans to establish a mission chain in the Valley were abandoned. In the early 20th century, when the upper Merced River basin lay mostly protected, the lower river was the subject of dam-building and irrigation diversions by the Merced Irrigation District. Classified as a "high hazard" structure, it was originally considered for inclusion on the National Register of Historic Places but was deemed too dangerous, and was subsequently removed. Little Yosemite Valley formed as a result of the underlying rock being harder than that below the Giant Staircase, the cliff wall containing Vernal Fall and Nevada Fall. When lateral moraines adjacent to each other join, they create medial moraines, which are also carried down on the surface of the moving ice. It is most well known for its swift and steep course through the southern part of Yosemite National Park, where it is the primary watercourse flowing through Yosemite Valley. Around 11,000 years ago, the terminus of the glacier was in the Rhne Valley and the glacier's edge reached almost as far as Riederfurka. Quick facts, basic science, and information about snow, ice, and why the cryosphere matters The cryosphere includes all of the snow and ice-covered regions across the planet. Many depositional landforms result from sediment deposited or reshaped by Since 1980 numerous small glacial lakes formed behind the new terminal moraines of several of these glaciers. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were formed at the foot, marking the maximum advance of the glacier. Over millions of years, the Merced cut a deep canyon through the softer sedimentary rock, eventually hitting the hard granite beneath. When the ice under the till melts, the till slumps in and forms depressions called kettles. By late autumn the river level has dropped considerably, and some smaller tributaries dry up altogether. Together, these diversions remove almost half the natural flow of the Merced River, and an even greater proportion during dry years. In the mid-20th century, the flow in the Merced River diminished to such a degree that very few salmon returned to spawn in the lower section of the Merced River. We can also trace how the Great Aletsch Glacier has grown and receded in the landscape of the Aletsch Forest. These glaciers rose in branches upstream of Yosemite Valley, descending from the Merced River headwaters, Tenaya Canyon and Illilouette Creek. By the late 1950s and early 1960s, irrigation in the San Joaquin Valley was to such an extent that many of the rivers ran dry in sections. The Merced River drops over Nevada Fall and Vernal Fall, together known as the "Giant Staircase", then receives Illilouette Creek and flows into Yosemite Valley, where it meanders between pine forests and meadows that fill the valley floor. State Route 140 follows the river out of the west entrance to the national park, a few miles before the South Fork Merced River, the largest tributary, joins from the left. Glaciology (from Latin glacies 'frost, ice', and Ancient Greek () 'subject matter'; lit. In the late 1880s a flour mill, woolen mill and a few lumber mills were constructed at Merced Falls. [35] Glaciology (from Latin glacies 'frost, ice', and Ancient Greek () 'subject matter'; lit. [16] Common insects found along the river include mayflies, stoneflies and caddisflies. Camping throughout the upper Merced watershed is generally only permitted in designated campgrounds. [36], Irrigation with water from the Merced River continued to grow substantially until most of the arable land around the river, some 120,000 acres (490km2), was under cultivation. El Portal Road, constructed through Merced Canyon in 1926, put an end to passenger service on the railway, but operations continued until the mid-1940s, when major flooding occurred, destroying sections of the railroad.
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