The Great Glen Fault is a long strike-slip (transcurrent) fault that runs through its namesake the Great Glen

Great Glen

The Great Glen , also known as Glen Albyn or Glen More is a series of glens in Scotland running 100 kilometres from Inverness on the Moray Firth, to Fort William at the head of Loch Linnhe.The Great Glen follows a large geological fault known as the Great Glen Fault...

 (Glen Albyn) in Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

. However, the fault is actually much longer and over 400 million years old.

Location

Aligned northeast to southwest, the Great Glen Fault extends further southwest in a straight line through Loch Linnhe

Loch Linnhe

Loch Linnhe is a sea loch on the west coast of Scotland....

 and the Firth of Lorne

Firth of Lorne

The Firth of Lorn is a body of water on Scotland's west coast, in Argyll and Bute. It lies between the Isle of Mull to the northwest and the Isles of Kerrera, Seil and Luing along with parts of the Scottish mainland southwest of Oban on the southeast side...

, and then on into northwestern Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, directly through Lough Foyle

Lough Foyle

Lough Foyle, sometimes Loch Foyle , is the estuary of the River Foyle in Ulster. It starts where the Foyle leaves Derry. It separates the Inishowen Peninsula in County Donegal, Republic of Ireland from County Londonderry in Northern Ireland.-Transport:...

, Donegal Bay

Donegal Bay

Donegal Bay is an inlet in the northwest of Ireland. Three counties – Donegal to the north and west, Leitrim and Sligo to the south – have shorelines on the bay, which is bounded on the west by the Atlantic Ocean...

 and Clew Bay

Clew Bay

Clew Bay is a natural ocean bay in County Mayo, Ireland. It contains Ireland's best example of sunken drumlins. According to tradition, there is an island in the bay for every day of the year. The bay is overlooked by Croagh Patrick, Ireland's holy mountain, and the mountains of North Mayo. Clare...

. To the northeast the fault connects to the Walls Boundary Fault and the associated Melby Fault and Nesting Fault, before becoming obscured by the effects of Mesozoic rifting to the north of Shetland. The fault continues on the North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

n side of the North Atlantic Ocean, but is no longer part of a contiguous fault, as the complete fault was broken when the Mid-Atlantic Ridge

Mid-Atlantic Ridge

The Mid-Atlantic Ridge is a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South...

 formed 200 million years ago. The North American side of the fault runs through the length of northwestern Newfoundland, Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, as the Cabot Fault (Long Range Fault) and on into the Gulf of St. Lawrence. It is at least 300 miles (480 km) long.

History

The Great Glen Fault has a long movement history. It formed towards the end of the Caledonian orogeny

Caledonian orogeny

The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...

 (mountain building) associated with the collision between the Laurentia

Laurentia

Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...

 and Baltic

Baltic Shield

The Baltic Shield is located in Fennoscandia , northwest Russia and under the Baltic Sea. The Baltic Shield is defined as the exposed Precambrian northwest segment of the East European Craton...

 tectonic plates at the end of the Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 period continuing into the Early Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 (likely age range - 430-390 Ma (million years)). The movement at this time was sinistral (left-lateral), the same as the closely related set of faults sub-parallel to the main part of the Great Glen Fault, these include the Strathconon Fault and Strathglass Faults to the northwest and the Laggan Fault, Tyndrum Fault, and Ericht-Laidon Fault to the southeast. The second main phase of movement was during the Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

, this time with a dextral (right-lateral) sense. The exact timing is uncertain but associated folds within the Devonian are cut by members of the Late Carboniferous to Early Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 dyke

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...

 swarm. The Great Glen Fault had its final phase of movement during the Late Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 to Early Tertiary

Tertiary

The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...

. The displacement is estimated to be 64 miles (104 km).

Erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

 along the fault zone during Quaternary glaciation

Quaternary glaciation

Quaternary glaciation, also known as the Pleistocene glaciation, the current ice age or simply the ice age, refers to the period of the last few million years in which permanent ice sheets were established in Antarctica and perhaps Greenland, and fluctuating ice sheets have occurred elsewhere...

 formed the famous Loch Ness

Loch Ness

Loch Ness is a large, deep, freshwater loch in the Scottish Highlands extending for approximately southwest of Inverness. Its surface is above sea level. Loch Ness is best known for the alleged sightings of the cryptozoological Loch Ness Monster, also known affectionately as "Nessie"...

.

The fault is mostly inactive today, but occasional moderate tremors have been recorded over the past 150 years.