Markarfljót is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in the south of Iceland

Iceland

Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

. It is approximately 100 kilometers long.

The Markarfljót rises in the Rauðafossafjöll massif, east of the volcano Hekla

Hekla

Hekla is a stratovolcano located in the south of Iceland with a height of . Hekla is one of Iceland's most active volcanoes; over 20 eruptions have occurred in and around the volcano since 874. During the Middle Ages, Icelanders called the volcano the "Gateway to Hell."Hekla is part of a volcanic...

. The main sources for the river are the glaciers Mýrdalsjökull

Mýrdalsjökull

Mýrdalsjökull mire dale glacier" or " mire valley glacier") is a glacier in the south of Iceland. It is situated to the north of Vík í Mýrdal and to the east of the smaller glacier Eyjafjallajökull. Between these two glaciers is Fimmvörðuháls pass. Its peak reaches in height and in 1980 it covered...

 and Eyjafjallajökull

Eyjafjallajökull

Eyjafjallajökull is one of the smaller ice caps of Iceland, situated to the north of Skógar and to the west of Mýrdalsjökull. The ice cap covers the caldera of a volcano with a summit elevation of . The volcano has erupted relatively frequently since the last glacial period, most recently in...

. It flows through narrow gorges in the mountainous area between the glaciers Tindfjallajökull

Tindfjallajökull

Tindfjallajökull is a stratovolcano in the south of Iceland. It has erupted rocks of basaltic to rhyolitic composition, and a 5-km-wide caldera was formed during the eruption of the 54,000 year old Thórsmörk Ignimbrite....

 and Torfajökull

Torfajökull

Torfajökull is a rhyolitic stratovolcano and complex of subglacial volcanoes, located north of Mýrdalsjökull and south of Þórisvatn Lake, Iceland...

, then spreads in the wide sandur

Sandur

A sandur is a glacial outwash plain formed of sediments deposited by meltwater at the terminus of a glacier.- Formation :Sandar are found in glaciated areas, such as Svalbard, Kerguelen Islands, and Iceland...

 plains at Iceland's south coast, near Þórsmörk

Þórsmörk

Thórsmörk is a mountain ridge in Iceland that was named after the Norse god Thor . It is situated in the south of Iceland between the glaciers Tindfjallajökull and Eyjafjallajökull...

. The Markarfljót takes its course first north, then west of Þórsmörk and finally empties into the Atlantic west of Eyjafjallajökull.

One of the Markarfljót's tributaries is the river Krossá, flowing through Þórsmörk, which is notorious for sudden changes in its water level.

The highest discharge ever measured in the Markarfljót was 2100 m3/s in 1967, during the Steinholt jökulhlaup

Jökulhlaup

A jökulhlaup is a glacial outburst flood. It is an Icelandic term that has been adopted by the English language. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland which are triggered by geothermal heating and occasionally by a volcanic subglacial...

.

The first bridge over the river was opened in 1934 near Litli Dímon. It is 242 meters long and was at the time the longest bridge in Iceland. A second bridge was built in 1978 at Emstrur. A third bridge was opened in 1992 a few kilometers south of the first bridge.