The Slate Islands are a small archipelago in

Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh w ...

, Ontario, Canada, about south of the town of Terrace Bay. The island group, consisting of 15 islands in total, was created by a

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...

impact which formed a crater about wide. In 1985, the

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central C ...

government established the Slate Islands as a natural environment provincial park. The islands are notable for having Ontario's largest herd of

boreal woodland caribou The boreal woodland caribou (''Rangifer tarandus caribou''; but subject to a recent taxonomic revision. See Reindeer: taxonomy), also known as woodland caribou, boreal forest caribou and forest-dwelling caribou, is a North American subspecies o ...

Geography

The island group consists of two main islands (Patterson and Mortimer), five minor islands (McColl, Edmonds, Bowes, Delaute and Dupuis islands) and numerous islets. The total surface area is about . The nearby Leadman Group of islands, about east, is often considered part of the Slate Islands. This group includes Leadman, Cape, Spar and Fish Islands.

Human history

Human sites have been found on the islands dating to about 1000CE. A lighthouse was built on Patterson Island, the largest island, in 1903 to help ships locate the harbour at the nearby town of Jackfish, Ontario. The island is named after William Patterson, a former lieutenant-governor of

Saskatchewan Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North ...

. Later, a fishing station was built on McColl Island. The original forests on the islands were modified by logging and forest fires. Up until the 1940s, the islands were used to stockpile boomed logs from the mainland Lake Superior north shore for export on

lake freighter Lake freighters, or lakers, are bulk carrier vessels that operate on the Great Lakes of North America. These vessels are traditionally called boats, although classified as ships. Since the late 19th century, lakers have carried bulk cargoes of ma ...

s to pulp mills in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...

. In 1985, the Slate Islands were protected as an Ontario Natural Environment Provincial Park. The islands remoteness is enforced by almost of open, wild, Lake Superior water and its distance from any large communities. It is frequented by naturalists, fishing parties, sailors exploring this Great Lake, and recently by an increasing number of sea kayaking parties.

Fauna

The islands are home to woodland caribou which migrated by

ice bridge An ice bridge is a frozen natural structure formed over seas, bays, rivers or lake surfaces. They facilitate migration of animals or people over a water body that was previously uncrossable by terrestrial animals, including humans. The most signi ...

from the mainland most recently in 1907. They have been studied extensively from 1974 to 2007 by Dr. A.T. (Tom) Bergerud. The caribou are a classic example of

island biogeography Insular biogeography or island biogeography is a field within biogeography that examines the factors that affect the species richness and diversification of isolated natural communities. The theory was originally developed to explain the pattern o ...

in action; the islands are notable for species that are absent but present on the adjacent mainland (red squirrel, moose, white-tailed deer, and grouse). No ungulates were present on the islands until the caribou arrived in the early 1900s while predators have been present only sporadically. Caribou reached the highest population density in the world on the islands before the 1990s, with the herd estimated at 650 animals.Godwin (1996), p. 3 After a food shortage and die-off in 1990, the numbers were reduced to about 100. In 2012 there were about 200 caribou on the Slate Islands.

Wolves The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly u ...

reached the archipelago in the early 1990s, preying heavily on the caribou, but for reasons not entirely understood, they disappeared a few years later. Wolves are again present on the island since winter 2015/16 (or earlier) as evidenced by aerial observation and scat. The waters surrounding the Slate Islands have been protected from commercial fishing to preserve one of the last native stocks of

lake trout The lake trout (''Salvelinus namaycush'') is a freshwater char living mainly in lakes in northern North America. Other names for it include mackinaw, namaycush, lake char (or charr), touladi, togue, and grey trout. In Lake Superior, it can als ...

in Lake Superior. The Islands have been a source of lake trout brood stock used at the Dorion Fish Hatchery, and fingerlings are planted back to Lake Superior to restore the fishery.

Species

Mammals found on the islands include woodland caribou, grey wolf,

beaver Beavers are large, semiaquatic rodents in the genus ''Castor'' native to the temperate Northern Hemisphere. There are two extant species: the North American beaver (''Castor canadensis'') and the Eurasian beaver (''C. fiber''). Beavers a ...

muskrat The muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic rodent native to North America and an introduced species in parts of Europe, Asia, and South America. The muskrat is found in wetlands over a wide range of climates and habita ...

snowshoe hare The snowshoe hare (''Lepus americanus''), also called the varying hare or snowshoe rabbit, is a species of hare found in North America. It has the name "snowshoe" because of the large size of its hind feet. The animal's feet prevent it from sin ...

, red fox, meadow jumping mouse, and little brown bat. Bird species include

American bittern The American bittern (''Botaurus lentiginosus'') is a species of wading bird in the heron family. It has a Nearctic distribution, breeding in Canada and the northern and central parts of the United States, and wintering in the U.S. Gulf Coast ...

bald eagle The bald eagle (''Haliaeetus leucocephalus'') is a bird of prey found in North America. A sea eagle, it has two known subspecies and forms a species pair with the white-tailed eagle (''Haliaeetus albicilla''), which occupies the same nich ...

, Canada goose,

common loon The common loon or great northern diver (''Gavia immer'') is a large member of the loon, or diver, family of birds. Breeding adults have a plumage that includes a broad black head and neck with a greenish, purplish, or bluish sheen, blackish ...

great blue heron The great blue heron (''Ardea herodias'') is a large wading bird in the heron family Ardeidae, common near the shores of open water and in wetlands over most of North America and Central America, as well as the Caribbean and the Galápagos ...

, grey jay,

herring gull Herring gull is a common name for several birds in the genus '' Larus'', all formerly treated as a single species. Three species are still combined in some taxonomies: * American herring gull (''Larus smithsonianus'') - North America * European ...

red-breasted merganser The red-breasted merganser (''Mergus serrator'') is a diving duck, one of the sawbills. The genus name is a Latin word used by Pliny and other Roman authors to refer to an unspecified waterbird, and ''serrator'' is a sawyer from Latin ''serra ...

, and

peregrine falcon The peregrine falcon (''Falco peregrinus''), also known as the peregrine, and historically as the duck hawk in North America, is a cosmopolitan bird of prey ( raptor) in the family Falconidae. A large, crow-sized falcon, it has a blue-grey ...

. Amphibians present include blue-spotted salamander, boreal chorus frog, Cope's gray treefrog, western

American toad The American toad (''Anaxyrus americanus'') is a common species of toad found throughout Canada and the eastern United States. It is divided into three subspecies: the eastern American toad (''A. a. americanus''), the dwarf American toad (''A. a ...

, northern spring peeper, and wood frog.

Flora

The cooling effect of

makes the Slate Islands a particularly harsh habitat for its latitude. As a result, islands harbour arctic and alpine plant species such as alpine chickweed (at its most southerly occurrence),Pye (1997), p. 83 '' Dryas drummondii'' (not found again for 1600 km (1000 mi) north), and alpine bistort, an

Inuit Inuit (; iu, ᐃᓄᐃᑦ 'the people', singular: Inuk, , dual: Inuuk, ) are a group of culturally similar indigenous peoples inhabiting the Arctic and subarctic regions of Greenland, Labrador, Quebec, Nunavut, the Northwest Territories, ...

delicacy eaten with seal oil. These arctic disjuncts are reminders of ice ages and associated tundra conditions in this area in the past. Vascular plants found on the islands are: *balsam fir (''Abies balsamea'') *black spruce (''Picea mariana'') *eastern white cedar (''Thuja occidentalis'') *mountain ash (''Sorbus decora'') *trembling aspen (''Populus tremuloides'') *white birch (''Betula papyrifera'') *alpine bistort (''Bistorta vivipara'') *alpine chickweed (''Cerastium alpinum'') *alpine cliff fern (''Woodsia alpine'') *alpine sedge (''Carex glaciali'') *American dune grass (''Leymus mollis'') *American Mountain-ash (''Sorbus Americana'') *Appalachian fir-clubmoss (''Huperzia appalachiana'') *beach pea (''Lathyrus japonicus'') *bird's-eye primrose (''Primula mistassinica'') *black crowberry (''Empetrum nigrum'') *butterwort (''Pinguicula spp.'') *Canadian yew (''Taxa Canadensis'') *common butterwort (''Pinguicula vulgaris'') *creeping snowberry (''Gaultheria hispidula'') *cut-leaved anemone (''Anemone multifada'') *devil's club (''Oplopanax horridus'') *dwarf rattlesnake plantain (''Goodyera repens'') *entire-leaved mountain-avens (''Dryas integrifolia'') *goldie's round-leaved orchid (''Platanthera macrophyll'') *goldthread (''Coptis trifolia'') *heartleaf twayblade (''Listera cordata'') *horned dandelion (''Taraxacum ceratophorum'') *knotted pearlwort (''Sagina nodosa'') *Labrador tea (''Rhododendron groenlandicum'') *lady fern (''Athryium felix-femina'') *large-leaved sandwort (''Moehringia macrophylla'') *leafy lichen (''Peltigera spp.'') *low spike-moss (''Selaginella selaginoides'') *moonwort grape-fern (''Botrychium lunnaria'') *mountain avens/yellow dryas (''Dryas drummondii'') *mountain bladder fern (''Cystopteris montana'') *mountain cranberry (''Vaccinium vitis-idaea'') *mountain clubmoss (''Huperzia selago'') *mountain fir-moss (''Huperzia appalachiana'') *northern meadow sedge (''Carex praticola'') *northern white anemone (''Anemone parviflora'') *northern woodsia (''Woodsia alpina'') *old man’s beard (''Usnea spp.'') *prairie spikemoss (''Selaginella densa'') *prickly rose (''Rosa acicularis)'' *rand's goldenrod (''Solidago simplex ssp. Randii'') *red stemmed feather moss (''Pleurozium schreberi'') *reindeer lichen (''Cladonia rangiferina'') *rock tripe (''Umbilicaria spp.'') *rose twisted stalk (''Roseus streptosus'') *roundleaf shadbush (''Amelanchier sanguinea'') *scirpus sedge (''Carex scirpus'') *smooth woodsia (''Woodsia glabella'') *sphagnum moss (''Sphagnum spp.'') *spike trisetum (''Trisetum spicatum'') *stair-step moss (''Hylocomium splendens'') *viviparous knotweed (''Polygonum viviparum'') *white mountain-saxifrage (''Saxifraga paniculata'') *wild chives (''Allium schoenoprasum var. sibiricum'') *wild sarsaparilla (''Aralia nudicaulis'')

Geology

The islands are not made of

slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic ro ...

; the rock is mainly of metamorphosed volcanic rocks greater than 2.7 billion years old. Also present are sedimentary rocks of the Rove and Gunflint formations, approximately 1.85-2.10 billion years old. There is evidence that about 1.1 billion years ago, there was volcanic centre on Paterson Island, however almost all volcanic rocks have been removed by erosion.Pye (1997), p. 84 The youngest rocks are

diatreme A diatreme, sometimes known as a maar-diatreme volcano, is a volcanic pipe formed by a gaseous explosion. When magma rises up through a crack in Earth's crust and makes contact with a shallow body of groundwater, rapid expansion of heated water ...

s, referring to

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...

-filled

volcanic pipe Volcanic pipes or volcanic conduits are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. They are considered to be a type of '' diatreme''. Volcanic pipes are composed of a deep, narrow cone ...

s that were formed by gaseous explosions. They occur as dikes or sills which criss-cross the all older rocks types. Also located in the islands are good examples of shatter cones, rare geological features formed in bedrock by the high velocity shock waves created by meteorite impacts. They have a distinctively conical shape with thin grooves (striae) that radiate from the top (apex) of the cone. The Slate Islands are home to a shatter cone measuring , one of the largest examples in the world (pictured here). Allogenic

is present, notably on the east and north sides of the islands.

Impact crater

The Slate Islands mark the centre of a large

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

. The original crater rim is estimated at about in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid fo ...

, but this and most of the crater has subsequently eroded away, leaving the islands which are interpreted as a central uplift. The age of the

impact event An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or ...

is estimated to be about 450 million years (

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

). Another source estimates the age at 800-500 million years (late

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

to early

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

).Sharpton, Dressler, (1996), p. 1178 It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor event, including the Decorah crater in Iowa, the

Ames crater Ames crater is a meteorite crater (astrobleme) in Major County, Oklahoma, United States. Ames, Oklahoma is near the center of the structure, which is southwest of Enid, Oklahoma.

in Oklahoma, and the Rock Elm crater in Wisconsin.

Provincial park

The Slate Islands Provincial Park was established in 1985 to protect the biodiversity and provincially significant elements of the natural and cultural landscape, and to maintain the islands' ecology by controlling development and focusing recreational use. While it is a non-operating park, some facilities are available, such as a dock, warm-up shelter, and five backcountry campsites. Permitted activities include boating, camping, canoeing, fishing, and hiking. It is only accessible via boat or floatplane.

References

Bibliography

* * Pye, E.G. (1997). ''Roadside Geology of Ontario: North Shore of Lake Superior'', Ontario GEOservices Centre, ROCK ON Series 2. * Sharpton, V.L. and Dressler, B.O. 'The Slate Islands Impact Structure: Structural Interpretation and Age Constraints', ''Lunar and Planetary Science''. March 1996: vol. 27 * Godwin, L. (February 1996
"Woodland Caribou in Northwestern Ontario - Why they are different..."
''Northwestern Ontario Boreal Forest Management Technical Note TN-07''

External links

*
Aerial exploration of the Slate Islands Impact Crater
{{Ontario parks Impact craters of Ontario Ordovician impact craters Landforms of Thunder Bay District Islands of Lake Superior in Ontario Archipelagoes of Canada