Ice age map

Wind the clock back 21,000 years. The ocean stands 130 metres lower, Siberia touches Alaska, the North Sea is a hunting ground and a wall of ice sits where Toronto and Stockholm are today.

What this map shows

The map above is the modern world with one number changed: the height of the sea. Pull the slider to any moment in the last 21,000 years and the ocean drops to where it stood then. Every piece of today's seabed that was above the water at that time turns sand-coloured, and the white sheets mark where the great ice caps lay. Pick a place from the list, search for any town, or tap the map to learn how far away the coast was from that spot.

Nothing here is a guess drawn by hand. The land that appears comes from real depth soundings of the sea floor, the water level follows a published reconstruction of global sea level, and the ice follows the mapped limits of the sheets at their largest. The page is built to answer a simple question for any coast on Earth: what was here when the mammoths were alive?

The ice age map at 21,000 years ago: a wide plain of exposed seabed joins Siberia and Alaska across the Bering Strait, with ice sheets on the mountains — Beringia at 21,000 years ago. The Bering Strait and most of the Chukchi Sea are dry land, a plain roughly 1,000 km from north to south.

Why the ocean was 130 metres lower

Water does not vanish from a planet. During the last glacial period it was simply parked somewhere else: in ice sheets up to 3 or 4 km thick that covered Canada, the northern United States, Scandinavia, the British Isles and the shelves of the Arctic. Enough water left the ocean to lower it by about 120 to 134 metres at the peak, 26,000 to 20,000 years ago. Geologists call this the Last Glacial Maximum.

The continental shelves are shallow, often less than 100 metres deep, so a drop of that size exposed enormous areas of them. The sea floor between Britain and Denmark, between Siberia and Alaska, between Malaysia and Borneo, and between Australia and New Guinea all became land. Rivers crossed these plains, animals grazed them and people lived on them. Then the ice melted, the water came back, and the plains went under in a few thousand years.

Reconstruction of a group of woolly mammoths walking across a cold steppe with snow-covered hills behind — Woolly mammoths on the mammoth steppe, the grassland that stretched from Spain to Alaska across the exposed shelves. Illustration: Mauricio Antón / Wikimedia Commons, CC BY 2.5

When the sea came back

The rise was not steady. For several thousand years after the peak the ice barely moved. Then, from about 16,500 years ago, the sheets began to collapse, and the ocean rose by roughly 12 metres every thousand years until 8,000 years ago, with one burst around 14,500 years ago (Meltwater Pulse 1A) when it jumped about 20 metres in five centuries. The slider on this map follows the reconstruction by Lambeck and colleagues, published in 2014, rounded to whole metres:

Years ago	Sea level	What was happening
21,000	−134 m	Last Glacial Maximum, ice at its largest
18,000	−124 m	Slow early melting
15,000	−103 m	Ice sheets collapsing, people in Beringia
14,000	−78 m	Just after Meltwater Pulse 1A
12,000	−58 m	Younger Dryas cold snap, rise almost stops
10,000	−41 m	Rapid rise resumes, Sundaland breaking up
8,000	−14 m	Doggerland reduced to islands
6,000	−3 m	Most ice gone, coastlines near their modern shape
0	0 m	Today

Chart of global sea level over the last 24,000 years rising from about minus 120 metres to today, with a steep section between 15,000 and 8,000 years ago — Sea level since the glacial maximum from coral and sediment records. The steep middle section is the main melt. Chart: Robert A. Rohde / Wikimedia Commons, CC BY-SA 3.0

The lost lands

Beringia

Set the slider to 21,000 years and look at the Bering Strait. The strait is only 50 metres deep, so it closed early and stayed shut for tens of thousands of years. The plain that replaced it, Beringia, was dry, windy grassland rather than the wet tundra of today, and it was full of grazing animals: mammoths, horses, steppe bison and the lions that hunted them. People lived here too, and from here they walked into the Americas by 16,000 years ago, possibly much earlier. The sea closed the strait again around 11,000 years ago.

Animated map of the Bering land bridge shrinking as sea level rises from 21,000 years ago to the present — The Bering land bridge flooding over the last 21,000 years. Animation: NOAA / Wikimedia Commons, public domain

Doggerland

The southern North Sea is nowhere deeper than 50 metres, and at the glacial maximum all of it was land: a plain of rivers, lakes and marshes joining Britain to the Netherlands, Germany and Denmark. Archaeologists call it Doggerland after the Dogger Bank, a sandbank that is the last high ground of that plain. Fishing boats keep bringing up its past: mammoth bones, harpoons carved from antler, flint tools and peat with tree roots still in it. By 8,000 years ago the rising sea had cut Doggerland down to a large island on the bank. Around 8,150 years ago a huge underwater landslide off Norway, the Storegga slide, sent a tsunami across what was left, and within a few more centuries it was all under water.

The ice age map at 18,000 years ago: the whole southern North Sea between Britain and the Netherlands is dry land, with ice sheets over Scandinavia and northern Britain — Doggerland at 18,000 years ago on this map, with the merged British and Scandinavian ice sheets to the north.

Schematic map of Doggerland showing its coastline around 10,000 years ago, with rivers running across the plain between Britain and continental Europe — Doggerland as it is usually drawn, around 10,000 years ago, with the Dogger Bank already an island in the north. Map: Max Naylor / Wikimedia Commons, CC BY-SA 3.0

Sundaland

The biggest lost land of all is in Southeast Asia. The sea between Malaysia, Sumatra, Java and Borneo is shallow, mostly under 40 metres, and at the glacial maximum it was a single landmass larger than India, called Sundaland. Rivers that now end at the coast of Sumatra and Borneo once joined in the middle of what is now the South China Sea. Sundaland drowned fast, between about 14,000 and 8,000 years ago, and its coastline moved inland by hundreds of kilometres in a few human lifetimes.

The ice age map at 21,000 years ago over Southeast Asia: Sumatra, Java and Borneo are joined to the mainland by a wide plain of exposed seabed — Sundaland on this map. The Java Sea and the Gulf of Thailand are dry; Borneo is part of the mainland.

Sahul

Across the Wallace Line the same thing happened to Australia: joined to New Guinea across the Torres Strait and to Tasmania across Bass Strait, it formed a continent called Sahul. The deep water of the Timor Sea and the Banda Sea never closed, which is why the first Australians, at least 50,000 years ago, had to cross open sea to get there. Bass Strait flooded about 12,000 years ago and the Torres Strait about 8,000 years ago.

The Persian Gulf, the Black Sea and Florida

The Persian Gulf averages only 35 metres deep, so for most of the glacial period it was a river valley: the Tigris and Euphrates ran across its floor and reached the sea only at the Strait of Hormuz. The Black Sea was cut off from the Mediterranean by the shallow sill of the Bosporus and became a lake standing well below the ocean, with a dry plain across its north-western shelf. Florida was about twice its present width, with the Gulf of Mexico coast up to 150 kilometres west of Tampa. Springs that are now on the sea floor were watering holes for mastodons and for the first people in Florida.

Where the ice was

At the glacial maximum the Laurentide ice sheet covered Canada and reached as far south as New York, Chicago and Seattle. Its surface stood over 3 kilometres above the ground near Hudson Bay; the weight pressed the crust down so far that the land there is still rising today. The Scandinavian sheet buried Norway, Sweden, Finland and the Baltic and joined the British sheet across the northern North Sea. Smaller caps sat on the Alps, the Pyrenees, the Andes, Patagonia, New Zealand and the mountains of Siberia.

On this map the ice follows the compiled outlines of the sheets at their largest. As you move the slider towards the present each sheet fades at roughly the time it disappeared: the British sheet by 15,000 years ago, Scandinavia by about 10,000, the Laurentide ice last of all around 7,000 years ago. Greenland and Antarctica never melted and are shown throughout.

Polar map of the Northern Hemisphere showing the ice sheets of the last glacial maximum over North America, Greenland and northern Europe — Northern Hemisphere ice at the glacial maximum. The sheets held enough water to lower the oceans by about 120 metres. Map: Hannes Grobe, AWI / Wikimedia Commons, CC BY 2.5

The ice age map zoomed out over the North Atlantic at 21,000 years ago, with white ice sheets over Canada, Greenland, Iceland, Britain and Scandinavia — The North Atlantic at the glacial maximum on this map, with ice on both sides of the ocean.

How the map is made

The exposed seabed comes from the same elevation data as the rest of HazardSim: a global grid that includes ocean depths from the ETOPO1 model, at roughly 2 kilometres per cell in the sea. A cell is painted as land when it lies below today's sea surface and above the sea level you have chosen. Lakes and basins that are below sea level but cut off from the ocean, such as the Caspian Sea, the Dead Sea and the Qattara Depression, are left alone. The area figure in the panel adds up the painted cells in view.

The sea level curve is the ice-volume reconstruction of Lambeck et al. (2014). The ice sheet outlines are the best-estimate glacial maximum reconstruction of Batchelor et al. (2019) for the Northern Hemisphere and the compilation of Ehlers, Gibbard and Hughes (2011) for the south, simplified for the web. The dates at which each sheet fades are approximate.

Two things the map does not do. It does not model the land itself moving: the crust under the ice sheets was pushed down by hundreds of metres and is still rebounding, so coasts near the former ice (Scandinavia, Hudson Bay, Scotland) were in a different place than a simple sea level drop suggests. And it does not model rivers, deltas or the sediment that has built up since, so the ancient plains looked rougher and wetter than a flat sand colour can show.

Questions

How much lower was the sea during the ice age?

About 120 to 134 metres lower than today at the peak, 26,000 to 20,000 years ago, depending on the reconstruction. This map uses 134 metres at 21,000 years ago.

Could people really walk from Asia to America?

Yes. The Bering Strait is shallow, so it was dry land from roughly 30,000 to 11,000 years ago. Archaeological sites show people in Alaska and further south by 16,000 years ago, and some finds suggest earlier.

Where was Doggerland and when did it sink?

Under the southern North Sea between England, the Netherlands and Denmark. It shrank as the sea rose, was an island by about 8,000 years ago and was gone a few centuries after the Storegga tsunami of about 8,150 years ago.

Is the sea still rising from the ice age?

The melt from the great ice sheets finished about 6,000 years ago, and the sea was close to its present level from then until the 20th century. The rise measured today, about 3 to 4 mm a year, comes from warming oceans and modern glacier loss. To see where that leads, use the sea level rise map.

Can I put this map on my own website?

Yes. Press Embed in the panel above the map, copy the code and paste it into your page. The embedded map opens at the place and the year you chose, and it is free to use as long as the HazardSim link stays.

Places to look at

Ice age map

What this map shows

Why the ocean was 130 metres lower

When the sea came back