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109-605: The Boundary Waters Canoe Area Wilderness ( BWCAW or BWCA ) comprises 1,090,000 acres (440,000 ha) of pristine forests, glacial lakes, and streams in the Superior National Forest . Located entirely within the U.S. state of Minnesota at the Boundary Waters , the wilderness area is under the administration of the United States Forest Service . Efforts to preserve the primitive landscape began in

218-468: A 20-year ban on mining upstream from the BWCAW. The BWCAW attracts over 150,000 visitors per year. It contains more than 2,000 backcountry campsites, 1,200 miles (1,900 km) of canoe routes, and 12 different hiking trails and is popular for canoeing , canoe touring , fishing, backpacking , dog sledding , and enjoying the area's remote wilderness character. Permits are required for all overnight visits to

327-406: A Boundary Waters National Recreation Area (NRA) of 527,000 acres (213,000 ha), permitting logging and mechanized travel in the latter area and removing from wilderness designation a number of large scenic lakes such as La Croix, Basswood, Saganaga, and Seagull. The bill was strongly opposed by environmentalists. October 21, 1978, Boundary Waters Canoe Area Wilderness Act, U.S. Public Law 95-495,

436-408: A distinctive composition or mode or origin. Special names still in wide use include amphibolite, greenschist , phyllite, marble, serpentinite , eclogite, migmatite , skarn , granulite , mylonite, and slate. The basic classification can be supplemented by terms describing mineral content or texture. For example, a metabasalt showing weak schistosity might be described as a gneissic metabasalt, and

545-451: A distinctive layering called foliation (derived from the Latin word folia , meaning "leaves"). Foliation develops when a rock is being shortened along one axis during recrystallization. This causes crystals of platy minerals, such as mica and chlorite , to become rotated such that their short axes are parallel to the direction of shortening. This results in a banded, or foliated, rock, with

654-459: A large area of contiguous wilderness lakes and forests called the "Quetico-Superior country", or simply the Boundary Waters . Lake Superior lies to the south and east of the Boundary Waters. Nearly 20% of the BWCAW's total area, or 190,000 acres (77,000 ha), is water. Within the borders of the area are over 1,100 lakes and hundreds of miles of rivers and streams. Much of the other 80% of

763-464: A marble will not be identical with the amphibolite facies of a pelite. However, the facies are defined such that metamorphic rock with as broad a range of compositions as is practical can be assigned to a particular facies. The present definition of metamorphic facies is largely based on the work of the Finnish geologist, Pentti Eskola , with refinements based on subsequent experimental work. Eskola drew upon

872-522: A metamorphic rock to be classified in this manner, the protolith should be identifiable from the characteristics of the metamorphic rock itself, and not inferred from other information. Under the British Geological Survey's classification system, if all that can be determined about the protolith is its general type, such as sedimentary or volcanic, the classification is based on the mineral mode (the volume percentages of different minerals in

981-462: A mixed conifer-hardwood forest known as the North Woods , a transition province between the northern boreal forest and deciduous forests to the south. While the forest is dominated by Conifers that include several varieties of pine , fir , and spruce trees, principal deciduous species such as mountain ash , maple , aspen and paper birch are also rather common, note the paper birch, one of

1090-413: A pelite containing abundant staurolite might be described as a staurolite pelite. [REDACTED] A metamorphic facies is a set of distinctive assemblages of minerals that are found in metamorphic rock that formed under a specific combination of pressure and temperature. The particular assemblage is somewhat dependent on the composition of that protolith, so that (for example) the amphibolite facies of

1199-403: A permit must be filled out at the permit stations located at each entry point. Each permit must specify the trip leader, the specific entry point and the day of entry. The permits are for an indefinite length, although visitors are only allowed one entry into the wilderness and cannot stay in one campsite for more than 14 nights. The BWCAW contains a variety of hiking trails. Shorter hikes include

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1308-532: A pit latrine and a fire grate, and no permits or fees. Additionally, dispersed camping is permitted anywhere on undeveloped public land without permit or fee. An exception is made for the designated wilderness of the Boundary Waters Canoe Area, which requires special permits for entrance. Tofte Ranger District In January 2023, the Biden administration set a 20-year moratorium on mining in 225,000 acres of

1417-519: A relatively mild grade of metamorphism, at temperatures of 350–500 °C (662–932 °F) and pressures of 200–500 MPa (2,000–5,000 bar). They can be divided into a lower group of metabasalts, including rare meta komatiites ; a middle group of meta-intermediate-rock and meta-felsic-rock; and an upper group of metasedimentary rock. The greenstone belts are surrounded by high-grade gneiss terrains showing highly deformed low-pressure, high-temperature (over 500 °C (932 °F)) metamorphism to

1526-410: A variety of metamorphic facies. Where subduction is taking place, the basalt of the subducting slab is metamorphosed to high-pressure metamorphic facies. It initially undergoes low-grade metamorphism to metabasalt of the zeolite and prehnite-pumpellyite facies , but as the basalt subducts to greater depths, it is metamorphosed to the blueschist facies and then the eclogite facies . Metamorphism to

1635-417: Is a great variety of metamorphic rock types. In general, if the protolith of a metamorphic rock can be determined, the rock is described by adding the prefix meta- to the protolith rock name. For example, if the protolith is known to be basalt , the rock will be described as a metabasalt. Likewise, a metamorphic rock whose protolith is known to be a conglomerate will be described as a metaconglomerate . For

1744-420: Is a popular activity in the BWCAW. Game species include northern pike , walleye , largemouth bass , smallmouth bass , and occasional panfish . Trout including brook trout , lake trout , rainbow trout and splake are also found. White sucker, burbot, and whitefish also occur. Limited stocking of walleye and lake trout is done on some lakes where natural recruitment is limited. The wilderness contains one of

1853-426: Is called a paired metamorphic belt . The main islands of Japan show three distinct paired metamorphic belts, corresponding to different episodes of subduction. Metamorphic rock is also exposed in metamorphic core complexes , which form in region of crustal extension. They are characterized by low-angle faulting that exposes domes of middle or lower crust metamorphic rock. These were first recognized and studied in

1962-511: Is dominated by metamorphic rock that has reached the amphibolite facies. Within the upper crust, which is the only part of the Earth's crust geologists can directly sample, metamorphic rock forms only from processes that can occur at shallow depth. These are contact (thermal) metamorphism , dynamic (cataclastic) metamorphism , hydrothermal metamorphism , and impact metamorphism . These processes are relatively local in occurrence and usually reach only

2071-584: Is estimated to contain 455,000 acres (184,000 ha) of old growth forest , woods that may have burned but have never been logged. Before fire suppression efforts began during the 20th century, forest fires were a natural part of the Boundary Waters ecosystem, with recurrence intervals of 30 to 300 years in most areas. On July 4, 1999, a powerful wind storm, or derecho , swept across Minnesota, central Ontario, and southern Quebec. Winds as high as 100 miles per hour (160 km/h) knocked down millions of trees, affecting about 370,000 acres (150,000 ha) within

2180-476: Is formed as tectonic plates move apart. Hydrothermal metamorphism is extensive here. This is characterized by metasomatism by hot fluids circulating through the rock. This produces metamorphic rock of the greenschist facies. The metamorphic rock, serpentinite , is particularly characteristic of these settings, and represents chemical transformation of olivine and pyroxene in ultramafic rock to serpentine group minerals. Contact metamorphism takes place when magma

2289-403: Is injected into the surrounding solid rock ( country rock ). The changes that occur are greatest wherever the magma comes into contact with the rock because the temperatures are highest at this boundary and decrease with distance from it. Around the igneous rock that forms from the cooling magma is a metamorphosed zone called a contact aureole . Aureoles may show all degrees of metamorphism from

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2398-452: Is instituted by the U.S. Forest Service. Cans and glass bottles are prohibited from the Boundary Waters. According to the U.S. Forest Service, the measure is expected to reduce refuse by 360,000 pounds (160 t), saving $ 90,000 per year on cleanup. October 1975, Eighth District Representative James Oberstar (D-MN) introduced a bill that if passed would have established a Boundary Waters Wilderness Area of 625,000 acres (253,000 ha) and

2507-405: Is known as burial metamorphism . This tends to produce low-grade metamorphic rock. Much more common is metamorphic rock formed during the collision process itself. The collision of plates causes high temperatures, pressures and deformation in the rocks along these belts. Metamorphic rock formed in these settings tends to shown well-developed schistosity. Metamorphic rock of orogenic belts shows

2616-712: Is located in Cook , Lake , and Saint Louis counties in northeastern Minnesota. Forest headquarters are located in Duluth , outside the boundaries of the forest. There are local ranger district offices in Aurora , Cook , Ely , Grand Marais , and Tofte . The forest covers 3.9 million acres (6,100 mi or 16,000 km ), and has over 445,000 acres (1,800 km ) of water. Its waters include some 2,000 lakes and rivers, more than 1,300 miles (2,100 km) of cold water streams, and 950 miles (1,530 km) of warm water streams. Many of

2725-435: Is not the deposition of glacial drift (unlike most of the rest of Minnesota), but the remodeling of the landscape by the scraping away of softer surfaces down to bare hard rock. The land therefore is raw, with many outcroppings of ancient bedrock, overlain in places by thin layers of gravelly soil and, in the west, silts deposited by Glacial Lake Agassiz . The forest contains a small slice of true boreal forest ( taiga ), and

2834-506: Is sufficiently hard and dense that it is difficult to quarry. However, some quartzite is used as dimension stone , often as slabs for flooring, walls, or stairsteps. About 6% of crushed stone, used mostly for road aggregate, is quartzite. Marble is also prized for building construction and as a medium for sculpture. Schistose bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness. A hazard may exist even in undisturbed terrain. On August 17, 1959,

2943-408: Is the most popular method of exploring the BWCAW. A 2007 study found more than 94% of overnight visitors used a non-motorized boat to travel through the park. The BWCAW's size and abundance of campsites, lakes, rivers and portage trails allow for almost countless options for different routes. Many online maps and guidebooks offer suggested routes based on entry point, duration and difficulty. Fishing

3052-545: Is transformed physically or chemically at elevated temperature, without actually melting to any great degree. The importance of heating in the formation of metamorphic rock was first noted by the pioneering Scottish naturalist, James Hutton , who is often described as the father of modern geology. Hutton wrote in 1795 that some rock beds of the Scottish Highlands had originally been sedimentary rock but had been transformed by great heat. Hutton also speculated that pressure

3161-400: Is uncertain. Special classifications exist for metamorphic rocks with a volcaniclastic protolith or formed along a fault or through hydrothermal circulation . A few special names are used for rocks of unknown protolith but known modal composition, such as marble, eclogite , or amphibolite . Special names may also be applied more generally to rocks dominated by a single mineral, or with

3270-426: Is used only when very little else is known about the rock that would allow a more definite classification. Textural classifications may be prefixed to indicate a sedimentary protolith ( para- , such as paraschist) or igneous protolith ( ortho- , such as orthogneiss). When nothing is known about the protolith, the textural name is used without a prefix. For example, a schist is a rock with schistose texture whose protolith

3379-475: Is usually devoid of schistosity and forms a tough, equigranular rock. If the rock was originally banded or foliated (as, for example, a laminated sandstone or a foliated calc- schist ) this character may not be obliterated, and a banded hornfels is the product. Contact metamorphism close to the surface produces distinctive low-pressure metamorphic minerals, such as spinel , andalusite, vesuvianite , or wollastonite . Similar changes may be induced in shales by

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3488-470: Is very low in silica) to metafelsic-rock (with a high silica content). Where the mineral mode cannot be determined, as is often the case when rock is first examined in the field , then classification must be based on texture. The textural types are: A hornfels is a granofels that is known to result from contact metamorphism. A slate is a fine-grained metamorphic rock that easily splits into thin plates but shows no obvious compositional layering. The term

3597-597: The American Bird Conservancy as a globally important bird habitat. Woodland caribou once inhabited the region but have disappeared due to encroachment by deer, and the effects of a brainworm parasite carried by deer which is harmful to both caribou and moose populations. Very rare sightings have been reported in nearby areas as recently as the 1980s. The north country was inhabited by the Paleo Indian culture circa 8000 BC. Limited artifacts have been found in

3706-566: The Basin and Range Province of southwestern North America, but are also found in southern Aegean Sea , in the D'Entrecasteaux Islands , and in other areas of extension. Continental shields are regions of exposed ancient rock that make up the stable cores of continents. The rock exposed in the oldest regions of shields, which is of Archean age (over 2500 million years old), mostly belong to granite-greenstone belts. The greenstone belts contain metavolcanic and metasedimentary rock that has undergone

3815-585: The Gunflint Trail , Echo Trail (County Road 116) and Fernberg Road (County Road 18) allow access to many wilderness entry points. The weather station Ely 25E is on the southern edge of Snowbank Lake (Minnesota) , a lake in the Boundary Waters Canoe Area Wilderness. Boundary Waters Canoe Area Wilderness has a dry winter humid continental climate ( Köppen Dwb ), bordering on a subarctic climate ( Köppen Dfc ). The lakes of

3924-704: The Kekekabic Trail . The Kekekabic Trail continues for another 39 miles (63 km), beginning near the Gunflint Trail and passing through the center of the BWCAW before exiting it near Snowbank Lake. Both the Border Route and the Kekekabic Trail are part of the longer North Country National Scenic Trail and together these represent the most remote segment of the NCT's 4,800 miles. Canoeing or other non-motorized boating

4033-717: The Misquah Hills including Eagle Mountain , the state's highest point, and other uplands along the Laurentian Divide separating the watershed of the Great Lakes and Atlantic Ocean from that of Hudson Bay and the Arctic Ocean. Despite the presence of dramatic cliffs and other local differences in elevation, the area is essentially flat, as it is part of an old peneplain eroded by weathering, water, and especially glaciers. The principal surficial result of recent glaciation

4142-589: The Ojibwe people, who traveled the waterways in canoes made of birch bark . Within the BWCAW are hundreds of prehistoric pictographs and petroglyphs on rock ledges and cliffs. It is thought that the Hegman Lake Pictograph located on a large overlooking rock wall on North Hegman Lake was most likely created by the Ojibwe. The pictograph appears to represent Ojibwe meridian constellations visible in winter during

4251-644: The Superior craton located near Ely, Minnesota, is up to 2.7 billion years old. Igneous rocks of the Duluth Complex comprise the bedrock of the eastern Boundary Waters. Ancient microfossils have been found in the banded iron formations of the Gunflint Chert . The Boundary Waters area is near the border of the true boreal forest and the Laurentian Mixed Forest Province (commonly called

4360-450: The atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact. Metamorphic rocks are characterized by their distinctive mineral composition and texture. Because every mineral is stable only within certain limits, the presence of certain minerals in metamorphic rocks indicates the approximate temperatures and pressures at which

4469-632: The bald eagle and other raptors , the ubiquitous common loon , and northern waterfowl . The Superior National Forest features a long segment of the 4,800-mile North Country National Scenic Trail [1] from just south of Burntside Lake by Ely to just south of Temperance River State Park near Schroeder. This segment includes (from West to East) the Kekekabic Trail, Border Route Trail, and Superior Hiking Trail. The Superior National Forest maintains developed fee campgrounds with amenities like drinking water and garbage disposal, rustic campgrounds without drinking water or fees, and backcountry campsites with only

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4578-402: The crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process. Metamorphic rocks are typically more coarsely crystalline than the protolith from which they formed. Atoms in the interior of a crystal are surrounded by a stable arrangement of neighboring atoms. This is partially missing at the surface of

4687-480: The "North Woods"), a transitional zone between the boreal forest to the north and the temperate hardwood forest to the south that contains characteristics of each. Trees found within the wilderness area include conifers such as red pine , eastern white pine , jack pine , balsam fir , white spruce , black spruce , and white-cedar , as well as deciduous birch , aspen , ash , and maple . Blueberries and raspberries can be found in cleared areas. The BWCAW

4796-471: The 1730s, La Vérendrye and others opened the region to trade, mainly in beaver pelts. By the end of the 18th century, the fur trade had been organized into groups of canoe-paddling voyageurs working for the competing North West and Hudson's Bay Companies, with a North West Company fort located at the Grand Portage on Lake Superior. The final rendezvous was held at Grand Portage in 1803, after which

4905-729: The 1900s and culminated in the Boundary Waters Canoe Area Wilderness Act of 1978. The area is a popular destination for canoeing , hiking, and fishing, and is the most visited wilderness in the United States. The BWCAW extends along 150 miles (240 km) of the Canadian border in the Arrowhead Region of Minnesota. The combined region of the BWCAW, Superior National Forest, Voyageurs National Park , and Ontario's Quetico and La Verendrye provincial parks make up

5014-480: The BWCAW and injuring 60 people. This event became known officially as the Boundary Waters–Canadian derecho , commonly referred to as "the Boundary Waters blowdown". Although campsites and portages were quickly cleared after the storm, an increased risk of wildfire due to the large number of downed trees became a concern. The U.S. Forest Service undertook prescribed burns to reduce the forest fuel load in

5123-756: The BWCAW are located in depressions formed by differential erosion of the tilted layers of the Canadian Shield . For the past two million years , massive sheets of ice have repeatedly scoured the landscape. The last glacial period ended with the retreat of the Laurentide Ice Sheet from the Boundary Waters about 17,000 years ago. The resulting depressions in the landscape later filled with water, becoming today′s lakes. Many varieties of Precambrian bedrock are exposed including: granite , basalt , greenstone , gneiss , as well as metamorphic rocks derived from volcanic and sedimentary rocks . Greenstone of

5232-631: The BWCAW from that era and the subsequent Archaic period circa 6000 years ago. Artifacts from the Early Woodland Era (circa 1300 years ago) have not been found there, but pottery and clay pipes from the Later Woodland Indians have been found there. The area was then sparsely populated by the Sioux . Then the Ojibwe arrived and the Sioux migrated westward. The area then became a part of the homeland of

5341-644: The BWCAW since 2008. According to the US forest service "This designation confirms what people in the area have enjoyed for thousands of years. Dark skies, starry nights, and astonishing northern lights displays have been part of the experience long before the area was designated wilderness..." Superior National Forest Under the administration of the United States Forest Service , the Superior National Forest comprises over 3,900,000 acres (6,100 mi or 16,000 km ) of woods and waters. The majority of

5450-408: The BWCAW. Quota permits are required for groups taking an overnight paddle, motor, or hiking trip, or a motorized day-use trip into the BWCAW from May 1 through September 30. These permits must be reserved in advance. Day use paddle and hiking permits do not require advance reservation and can be filled out at BWCAW entry points. From October 1 through April 30, permit reservations are not necessary, but

5559-538: The Boundary Waters regulations much as they are today, with limitations on motorboats and snowmobiles , a permit-based quota system for recreational access, and restrictions on logging and mining within the area. That same year the Forest Service began referring to it as "BWCAW" to recognize its wilderness character. Some aspects of the BWCAW's management and conservation have been controversial. A 1971 rule limiting visitors to "designated campsites" on heavy-use routes

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5668-452: The Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust. Some examples of metamorphic rocks are gneiss , slate , marble , schist , and quartzite . Slate and quartzite tiles are used in building construction. Marble is also prized for building construction and as a medium for sculpture. On

5777-435: The Earth's surface, where they are subject to high temperatures and the great pressure of the rock layers above. They can also form from tectonic processes such as continental collisions, which cause horizontal pressure, friction, and distortion. Metamorphic rock can be formed locally when rock is heated by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at

5886-619: The Moose, Farm and Seagull Chain of Lakes. 1999 – Trucks return to two of the three truck portages, Prairie and Trout Lake portages, as a result of Congressman Oberstar including this provision in his 1998 Transportation Bill. A snowmobile trail located 400 feet (120 m) from the border provoked a lawsuit in 2006. In 2015, a judge ruled that the snowmobile trail did not violate the Wilderness Act. It has been known for decades that there are about four billion tons of copper and nickel ore, "one of

5995-619: The North West Company moved its operations further north to Fort William (now Thunder Bay ). In 1821 the North West Company merged with the Hudson's Bay Company and the center of the fur trade moved even further north to the posts around Hudson Bay. During the late 18th and early 19th centuries, the area's legal and political status was disputed. The Treaty of Paris , which ended the American Revolutionary War in 1783, had defined

6104-566: The Ontario government to encourage them to preserve some of the area's land on their side of the border, noting that the area could be "an international forest reserve and park of very great beauty and interest". This collaboration led to the creation of the Superior National Forest and the Quetico Provincial Park in 1909. The BWCAW itself was formed gradually through a series of actions. By the early 1920s, roads had begun to be built through

6213-478: The Superior National Forest to promote public access to the area for recreation. In 1926 a section of 640,000 acres (260,000 ha) within the Superior National Forest was set aside as a roadless wilderness area by Secretary of Agriculture William Marion Jardine . This area became the nucleus of the BWCAW. In 1930, Congress passed the Shipstead-Newton-Nolan Act, which prohibited logging and dams within

6322-641: The Thye-Blatnik Bill authorized the government to purchase the few remaining privately owned homes and resorts within the area. In 1949, President Harry Truman signed Executive Order 10092 which prohibited aircraft from flying over the area below 4,000 feet. The area was officially named the Boundary Waters Canoe Area in 1958. The Wilderness Act of 1964 organized it as a unit of the National Wilderness Preservation System . The 1978 Boundary Waters Canoe Area Wilderness Act established

6431-467: The United States and Canada using the old trading route running along the Pigeon River and Rainy River (today the BWCAW's northern border). The BWCAW area remained largely undeveloped until gold, silver and iron were found in the surrounding area during the 1870s, 1880s and 1890s. Logging in the area began around the same time to supply lumber to support the mining industries, with production peaking in

6540-529: The University of MN conduct feasibility tests on the three truck portages. It is determined that trucks should remain. 1990 – Friends of the Boundary Waters, Sierra Club and six other environmental groups sue to have trucks removed; CWCS joins the U S Forest Service as intervenors. 1992 – Appeals court sides with U S Forest Service that trucks should remain. Friends of the Boundary Waters and coalition appeal to 8th Circuit Court of Appeals . Trucks are removed from

6649-477: The amphibolite or granulite facies. These form most of the exposed rock in Archean cratons. The granite-greenstone belts are intruded by a distinctive group of granitic rocks called the tonalite - trondhjemite - granodiorite or TTG suite. These are the most voluminous rocks in the craton and may represent an important early phase in the formation of continental crust. Mid-ocean ridges are where new oceanic crust

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6758-509: The area is forest. The BWCAW contains the largest remaining area of uncut forest in the eastern portion of the United States. The Laurentian Divide between the watersheds of the Great Lakes and Hudson Bay runs northeast–southwest through the east side of the BWCAW, following the crest of the Superior Upland and Gunflint Range . The crossing of the divide at Height of Land Portage was an occasion for ceremony and initiation rites for

6867-521: The area to preserve its natural water levels. Through additional land purchases and shifts in boundaries, the amount of protected land owned by the government in the area grew even further. In 1938, the area's borders were expanded and altered (roughly matching those of the present day BWCAW), and it was renamed the Superior Roadless Primitive Area. Additional laws focused on protecting the area's rustic and undeveloped character. In 1948,

6976-404: The bands showing the colors of the minerals that formed them. Foliated rock often develops planes of cleavage . Slate is an example of a foliated metamorphic rock, originating from shale , and it typically shows well-developed cleavage that allows slate to be split into thin plates. The type of foliation that develops depends on the metamorphic grade. For instance, starting with a mudstone ,

7085-420: The bulk composition of a rock. Hot fluids circulating through pore space in the rock can dissolve existing minerals and precipitate new minerals. Dissolved substances are transported out of the rock by the fluids while new substances are brought in by fresh fluids. This can obviously change the mineral makeup of the rock. However, changes in the mineral composition can take place even when the bulk composition of

7194-399: The burning of coal seams. This produces a rock type named clinker . There is also a tendency for metasomatism between the igneous magma and sedimentary country rock, whereby the chemicals in each are exchanged or introduced into the other. In that case, hybrid rocks called skarn arise. Dynamic (cataclastic) metamorphism takes place locally along faults . Here intense shearing of

7303-435: The circulation of fluids through buried rock, to the list of processes that help bring about metamorphism. However, metamorphism can take place without metasomatism ( isochemical metamorphism ) or at depths of just a few hundred meters where pressures are relatively low (for example, in contact metamorphism ). Metamorphic processes change the texture or mineral composition of the metamorphosed rock. Metasomatism can change

7412-427: The collision of tectonic plates at convergent boundaries . Here formerly deeply buried rock has been brought to the surface by uplift and erosion. The metamorphic rock exposed in orogenic belts may have been metamorphosed simply by being at great depths below the Earth's surface, subjected to high temperatures and the great pressure caused by the immense weight of the rock layers above. This kind of regional metamorphism

7521-491: The contact area to unmetamorphosed (unchanged) country rock some distance away. The formation of important ore minerals may occur by the process of metasomatism at or near the contact zone. Contact aureoles around large plutons may be as much as several kilometers wide. The term hornfels is often used by geologists to signify those fine grained, compact, non-foliated products of contact metamorphism. The contact aureole typically shows little deformation, and so hornfels

7630-612: The crystal, producing a surface energy that makes the surface thermodynamically unstable. Recrystallization to coarser crystals reduces the surface area and so minimizes the surface energy. Although grain coarsening is a common result of metamorphism, rock that is intensely deformed may eliminate strain energy by recrystallizing as a fine-grained rock called mylonite . Certain kinds of rock, such as those rich in quartz, carbonate minerals , or olivine, are particularly prone to form mylonites, while feldspar and garnet are resistant to mylonitization. Many kinds of metamorphic rocks show

7739-454: The early evening, knowledge of which may have been useful for navigating in the deep woods during the winter hunting season. The Grand Portage Indian Reservation , just east of the BWCAW at the community of Grand Portage , is home to a number of Ojibwe to this day. In 1688 the French explorer Jacques de Noyon became the first European known to have traveled through the BWCAW area. Later, during

7848-423: The eclogite facies releases a great deal of water vapor from the rock, which drives volcanism in the overlying volcanic arc . Eclogite is also significantly denser than blueschist, which drives further subduction of the slab deep into the Earth's mantle . Metabasalt and blueschist may be preserved in blueschist metamorphic belts formed by collisions between continents. They may also be preserved by obduction onto

7957-679: The event of a wildfire. The first major wildfire within the blowdown area occurred in August 2005, burning 1,335 acres (540 ha) between Alpine Lake and Seagull Lake in the northeastern BWCAW. In 2006, two fires at Cavity Lake and Turtle Lake burned more than 30,000 acres (12,000 ha). In May 2007, the Ham Lake Fire started near the location of the Cavity Lake fire, eventually covering 76,000 acres (31,000 ha) in Minnesota and Ontario and becoming

8066-564: The first time since the 1970s, as the Greenwood Fire threatened access and spread rapidly to the south of its origin, and other smaller fires were burning within the wilderness. Animals found in the BWCAW include deer , moose , beaver , timber wolves , black bears , bobcats , bald eagles , peregrine falcons , and loons . It is within the range of the largest population of wolves in the contiguous United States , as well as an unknown number of Canada lynx . It has also been identified by

8175-437: The following sequence develops with increasing temperature: The mudstone is first converted to slate, which is a very fine-grained, foliated metamorphic rock, characteristic of very low grade metamorphism. Slate in turn is converted to phyllite , which is fine-grained and found in areas of low grade metamorphism. Schist is medium to coarse-grained and found in areas of medium grade metamorphism. High-grade metamorphism transforms

8284-549: The forest is multiple-use, including both logging and recreational activities such as camping, boating, and fishing. Slightly over a quarter of the forest is set aside as a wilderness reserve known as the Boundary Waters Canoe Area (BWCA), where canoers can travel along interconnected fresh waters near land as well as over historic portages once used by Native American tribes and First Nations people, but later also by European explorers and traders. The forest

8393-559: The forest that are upstream of the Boundary Waters Canoe Area Wilderness. The moratorium protects the waters of the Rainy River watershed from pollution and blocks the proposed Twin Metals mine . [REDACTED] Media related to Superior National Forest at Wikimedia Commons Parts of this article were taken from the Forest Service website. As a work of the U.S. federal government ,

8502-446: The fur-trading Voyageurs of the 18th and early 19th centuries. The wilderness also includes the highest peak in Minnesota, Eagle Mountain (2,301 feet (701 m)), part of the Misquah Hills . Located around the perimeter of the BWCAW are six ranger stations: in Cook , Aurora , Ely , Isabella , Tofte and Grand Marais . The two nearby communities with most visitor services are Ely and Grand Marais. Several historic roads such as

8611-449: The identical composition, Al 2 SiO 5 . Likewise, forsterite is stable over a broad range of pressure and temperature in marble , but is converted to pyroxene at elevated pressure and temperature in more silicate-rich rock containing plagioclase , with which the forsterite reacts chemically. Many complex high-temperature reactions may take place between minerals without them melting, and each mineral assemblage produced indicates

8720-486: The lakes are located in depressions formed by the differential erosion of tilted layers of bedded rock; these depressions were given their final form by glacial scouring during recent ice ages . The forest is located on part of the Canadian Shield . The area is on a low plateau which is part of the Superior Upland . High points include the Sawtooth Mountains , a range of hills along the shore of Lake Superior ,

8829-448: The largest concentrations of native lake trout lakes in the lower 48 states. In 2020 the BWCA became a designated Dark Sky Sanctuary, one of 20 in the world. "It differs from other Dark Sky designations in that sanctuaries are the most remote and often darkest places in the world whose conservation state is 'most fragile'." The U.S. Forest Service had been working towards gaining this status for

8938-504: The largest population of gray wolves in the lower 48 states, with approximately 300-400 wolves within the boundaries of this forest. Ely's International Wolf Center protects all North American gray wolves from extinction. Located at the northern edge of the range of the hummingbird and near the southern edge of the range of the Canada jay , this forest has 163 nesting species of birds, the largest number of any national forest. Species include

9047-458: The late 1910s and gradually trailing off during the 1920s and 1930s. In 1902, Minnesota's Forest Commissioner Christopher C. Andrews persuaded the state to reserve 500,000 acres (200,000 ha) of land near the BWCAW from being sold to loggers. In 1905 he visited the area on a canoe trip and was impressed by the area's natural beauty. He was able to save another 141,000 acres (57,000 ha) from being sold for development. He soon reached out to

9156-437: The low-pressure facies, such as the hornfels and sanidinite facies . Most metamorphic rock is formed by regional metamorphism in the middle and lower crust, where the rock reaches the higher-pressure metamorphic facies. This rock is found at the surface only where extensive uplift and erosion has exhumed rock that was formerly much deeper in the crust. Metamorphic rock is extensively exposed in orogenic belts produced by

9265-576: The most extensive wildfire in Minnesota in 90 years. In 2011, the Pagami Creek Fire grew to over 92,000 acres (37,000 ha), spreading beyond the wilderness boundary to threaten homes and businesses. Smoke from the Pagami Creek Fire drifted east and south as far as the Upper Peninsula of Michigan , Ontario , Chicago , Poland, Ukraine, and Russia. In 2021, it was closed due to wildfire for

9374-474: The most numerous trees in the forest. Characteristic aquatic plants include water lilies and wild rice . Fish species such as walleye , northern pike , smallmouth bass , lake trout , brook trout , rainbow trout , and brown trout can be found in abundance in the forest's waters. Larger wildlife species include northern woodlands white-tailed deer , western moose , Canadian lynx , eastern black bear , and eastern wolf packs . Northern Minnesota has

9483-649: The northern border between the United States and Canada based on the inaccurate Mitchell Map . Ownership of the area between Lake of the Woods and Lake Superior was unclear, with the United States claiming the border was further north at the Kaministiquia River and Canada claiming it was further south beginning at the Saint Louis River . In 1842, the Webster–Ashburton Treaty clarified the border between

9592-453: The other hand, schist bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness. Metamorphic rocks form one of the three great divisions of rock types. They are distinguished from igneous rocks , which form from molten magma , and sedimentary rocks , which form from sediments eroded from existing rock or precipitated chemically from bodies of water. Metamorphic rocks are formed when existing rock

9701-460: The overriding plate as part of ophiolites . Eclogites are occasionally found at sites of continental collision, where the subducted rock is rapidly brought back to the surface, before it can be converted to the granulite facies in the hot upper mantle. Many samples of eclogite are xenoliths brought to the surface by volcanic activity. Many orogenic belts contain higher-temperature, lower-pressure metamorphic belts. These may form through heating of

9810-475: The rock by ascending magmas of volcanic arcs, but on a regional scale. Deformation and crustal thickening in an orogenic belt may also produce these kinds of metamorphic rocks. These rocks reach the greenschist , amphibolite, or granulite facies and are the most common of metamorphic rocks produced by regional metamorphosis. The association of an outer high-pressure, low-temperature metamorphic zone with an inner zone of low-pressure, high-temperature metamorphic rocks

9919-421: The rock does not change. This is possible because all minerals are stable only within certain limits of temperature, pressure, and chemical environment. For example, at atmospheric pressure, the mineral kyanite transforms to andalusite at a temperature of about 190 °C (374 °F). Andalusite, in turn, transforms to sillimanite when the temperature reaches about 800 °C (1,470 °F). All three have

10028-458: The rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous , sedimentary , or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by their protolith, their chemical and mineral makeup, and their texture . They may be formed simply by being deeply buried beneath

10137-423: The rock to gneiss , which is coarse to very coarse-grained. Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with distinctive growth habits, will not be foliated. Marble lacks platy minerals and is generally not foliated, which allows its use as a material for sculpture and architecture. Metamorphic rocks are one of the three great divisions of all rock types, and so there

10246-495: The rock typically forms mylonites. Impact metamorphism is unlike other forms of metamorphism in that it takes place during impact events by extraterrestrial bodies. It produces rare ultrahigh pressure metamorphic minerals, such as coesite and stishovite . Coesite is rarely found in eclogite brought to the surface in kimberlite pipes , but the presence of stishovite is unique to impact structures. Slate tiles are used in construction, particularly as roof shingle. Quartzite

10355-407: The rock underwent metamorphism. These minerals are known as index minerals . Examples include sillimanite , kyanite , staurolite , andalusite , and some garnet . Other minerals, such as olivines , pyroxenes , hornblende , micas , feldspars , and quartz , may be found in metamorphic rocks but are not necessarily the result of the process of metamorphism. These minerals can also form during

10464-486: The rock). Metasedimentary rocks are divided into carbonate-rich rock (metacarbonates or calcsilicate-rocks) or carbonate-poor rocks, and the latter are further classified by the relative abundance of mica in their composition. This ranges from low-mica psammite through semipelite to high-mica pelite . Psammites composed mostly of quartz are classified as quartzite. Metaigneous rocks are classified similarly to igneous rocks, by silica content, from meta-ultramafic-rock (which

10573-406: The sedimentary rock limestone and chalk change into larger crystals in the metamorphic rock marble . In metamorphosed sandstone, recrystallization of the original quartz sand grains results in very compact quartzite, also known as metaquartzite, in which the often larger quartz crystals are interlocked. Both high temperatures and pressures contribute to recrystallization. High temperatures allow

10682-416: The size of motors, and regulated the number of motorboats and long established motorized portages . It called for limiting the number of motorized lakes to 16 in 1984, and 14 in 1999, totaling about 24% of the area's water acreage. 1989 Truck portage testing. According to the 1978 BWCAW Act: Nothing in this Act shall be deemed to require the termination of the existing operation of motor vehicles to assist in

10791-404: The temperatures and pressures at the time of metamorphism. These reactions are possible because of rapid diffusion of atoms at elevated temperature. Pore fluid between mineral grains can be an important medium through which atoms are exchanged. The change in the particle size of the rock during the process of metamorphism is called recrystallization . For instance, the small calcite crystals in

10900-454: The text is in the public domain . Metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism . The original rock ( protolith ) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000  bar ) or more, causing profound physical or chemical changes. During this process,

11009-504: The three truck portages. 1994 – As a result of the Friends of the Boundary Waters lawsuit against the 1992 BWCAW Management Plan, canoe rests, pontoon boats and sailboats are banned from the Boundary Waters. 1999 – As a result of the Friends of the Boundary Waters lawsuit against the 1992 BWCAW Management Plan, the courts redefined the phrase ‘that particular lake’ and exempt permits were eliminated for property owners, resorts and outfitters on

11118-701: The trail to Eagle Mountain (7 miles (11 km)). Loop trails include the Pow Wow Trail , the Snowbank Trail , and the Sioux-Hustler Trail . The Border Route Trail and Kekekabic Trail are the two longest trails running through the BWCAW. The Border Route Trail runs east–west for over 65 miles (105 km) through the eastern BWCAW, beginning at the northern end of the Superior Hiking Trail and following ridges and cliffs west until it connects with

11227-556: The transport of boats across the portages from Sucker Lake to Basswood Lake, from Fall Lake to Basswood Lake, and from Lake Vermilion to Trout Lake, during the period ending January 1, 1984. Following said date, unless the Secretary determines that there is no feasible non-motorized means of transporting boats across the portages to reach the lakes previously served by the portages listed above, he shall terminate all such motorized use of each portage listed above. 1989 – U S Forest Service with

11336-451: The use of granulite as a classification for rock metamorphosed to the granulite facies. Instead, such rock will often be classified as a granofels. However, this approach is not universally accepted. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. The lower continental crust is mostly metamafic-rock and pelite which have reached the granulite facies . The middle continental crust

11445-409: The world's largest undeveloped mineral deposits", in the Duluth Complex , which underlies part of northeastern Minnesota. Resource companies have proposed mines south and west of the BWCAW upstream of the wilderness and within its watershed, leading to concerns that surface runoff could damage the wilderness. In December 2016 the federal government proposed banning mining for 20 years while the subject

11554-561: The zonal schemes, based on index minerals, that were pioneered by the British geologist, George Barrow . The metamorphic facies is not usually considered when classifying metamorphic rock based on protolith, mineral mode, or texture. However, a few metamorphic facies produce rock of such distinctive character that the facies name is used for the rock when more precise classification is not possible. The chief examples are amphibolite and eclogite . The British Geological Survey strongly discourages

11663-419: Was important in metamorphism. This hypothesis was tested by his friend, James Hall , who sealed chalk into a makeshift pressure vessel constructed from a cannon barrel and heated it in an iron foundry furnace. Hall found that this produced a material strongly resembling marble , rather than the usual quicklime produced by heating of chalk in the open air. French geologists subsequently added metasomatism ,

11772-522: Was signed by President Jimmy Carter . The act added 50,000 acres (20,000 ha) to the Boundary Waters, to then encompass 1,098,057 acres (444,368 ha), and extended greater wilderness protection to the area. The name was changed from the Boundary Waters Canoe Area to the Boundary Waters Canoe Area Wilderness. The Act banned logging, mineral prospecting, and mining, and all but bans snowmobile use (two snowmobile routes remain to access Canada). The act limited motorboat use to about two dozen lakes, limited

11881-615: Was studied. The Trump administration cancelled the study in September 2018, clearing the way for mining leases in the national forest. The Antofagasta PLC subsidiary Twin Metals Minnesota would operate a proposed mine. In October 2021, the Biden administration filed an application for a "mineral withdrawal" that will put a hold on the development of the mine proposal while the environmental impacts are studied. The completed study could lead to

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