Vatnajökull

Long ago, in the Ice Age, ice covered all of Iceland. Then most of it melted away.

Later, snow piled up on the high mountains again. Small glaciers grew and joined together into one giant ice cap.

Vatnajökull is not left over from the Ice Age. The national park explains that the great ice sheet that once covered all of Iceland melted away, and by about 9,000 years ago probably only small glaciers were left on the highest mountains.

As summers grew cooler again, glaciers on mountain ranges between 1,200 and 2,000 meters high grew and joined together. Computer models suggest they merged into one ice cap about 1,000 to 1,500 years ago. During a cold period called the Little Ice Age, the ice kept growing, and it reached its biggest size in thousands of years at the end of the 1800s.

The national park stresses that Vatnajökull is not a remnant of the Weichselian ice sheet of the Last Glacial Maximum, about 20,000 years ago. Lake sediments from Lagarfljót show no glacial input by about 9,000 years ago; in the warmest part of the Holocene (8,000–5,000 years ago) probably only small glaciers survived on the highest summits, and glacial meltwater returned to the lake about 4,500 years ago. Tree logs about 2,000 years old in the forefields of Fláajökull and Skaftafellsjökull show those valleys were then ice-free.

The modern ice cap formed as glaciers on ranges between 1,200 and 2,000 m coalesced, about 1,000–1,500 years ago according to numerical models; by the settlement of Iceland (around 874 CE) it was continuous. Cooling culminated in the Little Ice Age (about 1450–1900); the southern outlet glaciers reached the lowlands in the 17th and 18th centuries, and the ice cap reached its maximum Holocene size at the end of the 19th century. UNESCO notes the ice cap has varied in size over the past 2.8 million years.

Iceland sits where two big pieces of Earth slowly pull apart.

Volcanoes are hidden under Vatnajökull's ice. When one erupts, it melts the ice. The water can rush out in a big flood.

Iceland sits on the Mid-Atlantic Ridge, where two of Earth's plates are pulling apart, about 19 millimeters each year, UNESCO says. Deep below, a plume of hot rock supplies plenty of magma. So volcanoes lie under Vatnajökull's ice, including Grímsvötn and Bárðarbunga, two of the most active volcanoes in Iceland.

When a volcano under the ice erupts or heats the rock, ice melts and water collects under the glacier. It can burst out suddenly in a flood called a jökulhlaup, which means "glacier run". Eruptions under ice also build unusual mountains and ridges of a volcanic rock called hyaloclastite, which the national park says is rare elsewhere in the world.

UNESCO describes the property's setting: Iceland exposes the only part of the actively spreading Mid-Atlantic Ridge above sea level, with plates separating by about 19 mm a year, and two rift zones, the Eastern and Northern Volcanic Zones, intersect above a mantle plume. The property holds ten central volcanoes, eight beneath the ice; the national park says the ice cap itself conceals seven central volcanoes, including Grímsvötn, Bárðarbunga, Kverkfjöll and Öræfajökull, four of the most active in Iceland.

Subglacial eruptions are explosive as magma meets water, and the fragments quickly cement into hyaloclastite; during the Gjálp eruption of 1996 a 7 km hyaloclastite ridge formed beneath the ice. At Skaftárkatlar, Grímsvötn and Kverkfjöll, volcanic and geothermal heat sustain subglacial lakes that drain in jökulhlaups. Britannica records peak discharges of about 50,000 m³ per second in the Grímsvötn floods of 1934 and 1938, and the meltwater builds the vast sandur (outwash) plains north and south of the ice cap.

Tiny living things live in lakes under the ice!

Some animals live in water deep in the ground. People have farmed near the ice for more than a thousand years. They learned to live with floods.

Life finds a way even here. UNESCO says single-celled living things thrive in the dark, icy lakes hidden beneath the glacier, places that scientists think may be like early Earth or the icy moons of Jupiter and Saturn. Some animals that live in underground water in the volcanic zones, found nowhere else, survived the Ice Age there.

People have lived near the ice cap for more than a thousand years. The national park explains that farmers had to adapt to eruptions, glacier floods and rivers that destroyed farmland. In some places the glaciers advanced over old farms in the 1600s and 1700s, and those areas are now ice-free again.

UNESCO highlights endemic groundwater fauna in the volcanic zones that survived the ice age, and single-celled organisms that prosper in subglacial lakes, environments that may replicate conditions on early Earth and the icy satellites of Jupiter and Saturn.

The national park describes more than a millennium of human adaptation around the ice cap: farmland destroyed by eruptions, glacial rivers and soil erosion; southern settlements cut off by glacial rivers, where horses trained for river crossings were the main transport for centuries, until the last river on the Ring Road was bridged in 1974; and the Öræfi district devastated by the eruption of 1362, with more damage in 1727. Breiðamerkurjökull advanced over farms of Iceland's early settlers in the 17th and 18th centuries; some of that land is ice-free again and is now one of Iceland's most popular tourist destinations.

Vatnajökull is getting smaller.

The world is getting warmer, so the ice is melting faster. Scientists watch the glaciers closely to learn how they are changing.

Since its biggest size at the end of the 1800s, Vatnajökull has been shrinking. The national park says it has lost more than 15 percent of its volume in the last century, and all of its southern outlet glaciers are retreating and thinning at unprecedented rates.

Scientists call it one of the ice caps most sensitive to climate change in the world. As the ice pulls back, it leaves behind ridges of rock called moraines, which show where the glaciers once reached. That makes Vatnajökull a natural laboratory for studying how glaciers respond to a warming world.

UNESCO notes that the ice cap reached its greatest extent at the end of the 18th century (the national park gives the maximum Holocene size at the end of the 19th century) and has on average retreated since, with retreat accelerating in response to global warming. The national park reports a loss of more than 15% of its volume over the last century, describes all southern outlet glaciers as retreating and thinning at unprecedented rates, and ranks Vatnajökull among the most climate-sensitive ice caps worldwide because of its high mass turnover.

Well-preserved lateral and end moraines record the late-19th-century maximum, and accessible outlet glaciers make the area a flagship site for glacial research; UNESCO counted at least 281 peer-reviewed papers on the property in a decade. Some of the meltwater is used for hydropower.

Iceland's weather changes fast.

Check the weather before you go. Stay on marked paths. Leave stones and plants where you find them.

Most of Vatnajökull National Park is in Iceland's highlands, where summers are short and the weather is unpredictable. The park warns that roads can be damaged by floods, sandstorms and even snow at any time of year, and some highland roads cross rivers without bridges.

Before a trip, the park advises checking the weather forecast and road conditions and leaving a travel plan with Iceland's Safetravel service. Follow marked hiking routes, drive only on roads shown on the park's maps, and do not move stones or pick plants. Natural hazards such as eruptions and glacier floods are common here, so always follow warnings from the park.

The national park's travel advice notes that most of the park lies in the highlands, where summers are short, weather is unpredictable and roads can deteriorate from flooding, sandstorms and snow at any season; highland roads are often ill-defined gravel tracks with unbridged rivers, and driving is permitted only on roads marked on the park's maps. It recommends checking forecasts with the Icelandic Meteorological Office, road status with the Icelandic Road and Coastal Administration, the park's own area cautions, and registering travel plans on Safetravel.

UNESCO identifies risk management as a major issue in this highly dynamic setting where natural hazards are common, alongside wear and tear at popular sites as visitor numbers approached one million in 2017. Visitors protect the park by keeping to marked routes, camping only where permitted and leaving stones, plants and cultural remains undisturbed.