20,000 years ago the sea stood 120 m (395 ft) lower, and Puerto Rico, Vieques, Culebra and every Virgin Island but St. Croix were one island. The map drains the sea to that low on NOAA’s seabed, then lets it rise back and parts the islands in the order they really parted. St. Thomas and Tortola were one island until about 8,700 years ago.
The islands at today's sea level. Press play: the sea falls to where it stood at the coldest part of the last ice age, then rises back, and the islands come apart in the order they really did.
At the height of the last ice age, about 20,000 years ago, the sea stood about 120 m (395 ft) lower than today. Puerto Rico, Vieques, Culebra, St. Thomas, St. John, Jost Van Dyke, Tortola, Virgin Gorda and Anegada were one island, 349 km (217 mi) long and about 19,000 km² (7,300 sq mi). The rising sea cut it in two in the Virgin Passage about 9,600 years ago, and split the Virgin Islands from one another in a few centuries around 8,700 years ago. Water Island was the last to part, about 7,500 years ago. St. Croix was never part of it.
Each crossing below is the shallowest way across the seabed between two islands, measured on NOAA’s elevation grid. The islands were joined while the sea stood below it, and parted when the rising sea topped it.
| About | Crossing | What parted | Depth today | |
|---|---|---|---|---|
| 9,600 years ago | Virgin Passage | Puerto Rico, Vieques and Culebra from the Virgin Islands | 32 m (104 ft) | Replay ↑ |
| 9,000 years ago | Just west of Culebra | Culebra from Puerto Rico | 24 m (80 ft) | Replay ↑ |
| 9,000 years ago | North of Norman Island | Norman Island from the rest | 24 m (80 ft) | Replay ↑ |
| 8,800 years ago | North-east of Cooper Island | Salt and Cooper islands from the rest | 23 m (74 ft) | |
| 8,800 years ago | Between Jost Van Dyke and Tortola | Jost Van Dyke from Tortola | 23 m (74 ft) | |
| 8,700 years ago | Across the Sir Francis Drake Channel | Peter Island from Tortola | 21 m (69 ft) | |
| 8,700 years ago | The Narrows | The British islands from St. John | 20 m (67 ft) | Replay ↑ |
| 8,600 years ago | Pillsbury Sound | St. John from St. Thomas | 20 m (66 ft) | Replay ↑ |
| 8,600 years ago | Between Virgin Gorda and Anegada | Anegada from Virgin Gorda | 20 m (66 ft) | Replay ↑ |
| 8,600 years ago | The Dogs | Virgin Gorda from Tortola | 19 m (63 ft) | Replay ↑ |
| 7,900 years ago | Vieques Passage | Vieques from Puerto Rico | 13 m (43 ft) | Replay ↑ |
| 7,800 years ago | Between Salt Island and Cooper Island | Salt Island from Cooper Island | 13 m (41 ft) | Replay ↑ |
| 7,500 years ago | Between Water Island and St. Thomas | Water Island from St. Thomas | 11 m (35 ft) | Replay ↑ |
The sea rose about 120 m in 20,000 years, but not evenly. It rose fastest as the great ice sheets collapsed: two reef-crest corals off Barbados, 14,200 and 13,700 years old, grew 19 m apart in depth. It slowed after about 8,000 years ago and has been within a few metres of today for the last 5,000. The dots mark the moments on the map.
| Years ago | Sea level | Feet |
|---|---|---|
| 20,000 | -120.3 m | −395 ft |
| 19,000 | -116.8 m | −383 ft |
| 18,000 | -107.9 m | −354 ft |
| 17,000 | -105.4 m | −346 ft |
| 16,000 | -101.5 m | −333 ft |
| 15,000 | -97.7 m | −321 ft |
| 14,000 | -85.7 m | −281 ft |
| 13,000 | -67.0 m | −220 ft |
| 12,000 | -60.7 m | −199 ft |
| 11,000 | -44.5 m | −146 ft |
| 10,000 | -34.5 m | −113 ft |
| 9,000 | -24.9 m | −82 ft |
| 8,000 | -13.9 m | −46 ft |
| 7,000 | -8.5 m | −28 ft |
| 6,000 | -5.4 m | −18 ft |
| 5,000 | -3.6 m | −12 ft |
| 4,000 | -2.5 m | −8 ft |
| 3,000 | -1.8 m | −6 ft |
| 2,000 | -1.1 m | −4 ft |
| 1,000 | -0.5 m | −2 ft |
| Today | 0 m | 0 ft |
St. Croix sits on its own platform across the Virgin Islands Basin, which reaches about 4,500 m (15,000 ft) between St. Thomas and St. Croix. The shallowest way from St. Croix to the rest is more than 1,800 m (6,000 ft) down, many times deeper than the sea ever fell. Even at the ice-age low, St. Croix was an island on its own.
Yes. At the height of the last ice age, about 20,000 years ago, the sea stood about 120 m (395 ft) lower and Puerto Rico, Vieques, Culebra, St. Thomas, St. John, Tortola, Jost Van Dyke, Virgin Gorda and Anegada were one island about 19,000 km² (7,300 sq mi). The sea cut it in two in the Virgin Passage about 9,600 years ago.
About 120 m (395 ft) lower at the coldest point, around 20,000 years ago. The record comes from reef-crest corals off Barbados (Acropora palmata, which grows within a few metres of the surface), dated and found far below today's sea.
About 8,600 years ago, when the rising sea topped the shallowest crossing in Pillsbury Sound, 20 m (66 ft) below today's sea level. Water Island stayed joined to St. Thomas until about 7,500 years ago.
About 8,700 years ago. The shallowest crossing between St. John and Tortola, in the Narrows, is 20 m (67 ft) down; the sea topped it at almost the same time as Pillsbury Sound. Anegada parted from Virgin Gorda at about the same time.
No. St. Croix sits on its own platform across the Virgin Islands Basin, which reaches about 4,500 m (15,000 ft). The shallowest way across is more than 1,800 m (6,000 ft) down, far deeper than the sea ever fell.
They are the high points of one platform, the Puerto Rico Bank, which was dry land in the ice age and drowned as the sea rose. The shallowest crossings between the islands are only 11 to 32 m deep, while the basin south of them, toward St. Croix, reaches about 4,500 m (15,000 ft).
To within a few centuries. The map floods today's seabed, but reefs and sand have built up since and the islands have moved a little, and the sea-level curve itself carries an uncertainty of a few metres. The dates are rounded to the nearest hundred years for that reason.
The map floods today’s seabed to the sea level of each moment: any ground above the water is drawn as land. The seabed and the land are NOAA’s elevation grid at about 110 m; the moment two islands join or part is found by adding the grid’s cells from the highest to the lowest and noting the depth at which each pair first connects. The sea level for each moment comes from the corals off Barbados for 20,000 to 9,000 years ago, and from a curve held to the published Caribbean record since. Reefs and sand have built up on the seabed since the islands parted and the land has moved a little, so read the coastlines as a guide and the dates as good to a few centuries.