Ribbed moraines
Encyclopedia
A Rogen moraine is a subglacially (i.e. under a glacier
or ice sheet
) formed type of moraine
landform
, that mainly occur in Fennoscandia
, Scotland
, Ireland
and Canada
. They cover large areas that have been covered by ice, and occur mostly in what is believed to be the central areas of the ice sheets. Rogen moraines are named after Lake Rogen in Härjedalen
, Sweden
, the landform’s type locality.
The landform occurs in groups that are often closely and regularly spaced. They consist of glacial drift, with till
being the most common constituent. The individual moraines are large, wavy ridges orientated transverse to ice flow. Drumlins are often found in close proximity of Rogen moraines, and are often interpreted to be formed at the same time as the Rogen moraines. Although Rogen moraines can span a large range of sizes, the most common distribution seems to be 10-30 metres high, 150-300 metres wide and 300-1,200 metres long.
The exact mechanics of Rogen moraine formation are not known, but since the 1970’s, several theories on the formation have been proposed:
However, it has been suggested that, due to the diversity of morphological characteristics displayed by Rogen moraine, different processes might be able to create the landform. This means that all four of the processes mentioned above might be correct. The different theories that proposed a formation near or at the glacial margin have largely been abandoned. Some of these theories proposed that Rogen moraines had an origin as a series of end moraines, that they formed in association with calving ice termini in glacial lakes, or that Rogen moraines formed in dead-ice
, where supraglacial material fell down into crevasses in the ice.
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
or ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
) formed type of moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
landform
Landform
A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
, that mainly occur in Fennoscandia
Fennoscandia
Fennoscandia and Fenno-Scandinavia are geographic and geological terms used to describe the Scandinavian Peninsula, the Kola Peninsula, Karelia and Finland...
, 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...
, 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...
and 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...
. They cover large areas that have been covered by ice, and occur mostly in what is believed to be the central areas of the ice sheets. Rogen moraines are named after Lake Rogen in Härjedalen
Härjedalen
' is a historical province or landskap in the centre of Sweden. It borders the country of Norway as well as the provinces of Dalarna, Hälsingland, Medelpad, and Jämtland...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, the landform’s type locality.
The landform occurs in groups that are often closely and regularly spaced. They consist of glacial drift, with till
Till
thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....
being the most common constituent. The individual moraines are large, wavy ridges orientated transverse to ice flow. Drumlins are often found in close proximity of Rogen moraines, and are often interpreted to be formed at the same time as the Rogen moraines. Although Rogen moraines can span a large range of sizes, the most common distribution seems to be 10-30 metres high, 150-300 metres wide and 300-1,200 metres long.
The exact mechanics of Rogen moraine formation are not known, but since the 1970’s, several theories on the formation have been proposed:
- Megaripples eroded in the basal ice fill during subglacial outburst floods.
- Already existing landforms, such as drumlins and flutesFlute (glacial)A glacial flute is a landform created by the movement of a glacier around a boulder. They are long ridges on the ground parallel to the movement. Examples can be found in many places including Iceland, Alaska and Canada....
or marginal morainesTerminal moraineA terminal moraine, also called end moraine, is a moraine that forms at the end of the glacier called the snout.Terminal moraines mark the maximum advance of the glacier. An end moraine is at the present boundary of the glacier....
are reshaped due to a ~90° change in the direction of the ice flow. - Debris-rich basal ice or pre-existing sedimentSedimentSediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s are sheared and stacked, or folded during compressive ice flow. - Sediment sheets become fractured and extended during a transition of the overlying glacier from being cold based ice to warm based.
However, it has been suggested that, due to the diversity of morphological characteristics displayed by Rogen moraine, different processes might be able to create the landform. This means that all four of the processes mentioned above might be correct. The different theories that proposed a formation near or at the glacial margin have largely been abandoned. Some of these theories proposed that Rogen moraines had an origin as a series of end moraines, that they formed in association with calving ice termini in glacial lakes, or that Rogen moraines formed in dead-ice
Dead-ice
Dead-ice occurs when a glacier or ice sheet ceases to move and melts in situ. After the ice has melted it leaves behind a hummocky terrain produced by the deposition of glacio-fluvial sediments and ablation till as the ice melted. Such features include kettle holes...
, where supraglacial material fell down into crevasses in the ice.