The strait that wasn't there

This is the waterway that made the September 2026 headlines. By late September 2026, the Strait of Hormuz had been closed to most shipping for much of the war that began in late February. The picture shifted during September: preliminary Kpler data cited by Reuters on 29 September put crude flows through Hormuz at about 9.7 million barrels a day for the month. That estimate measures physical exports; it does not establish a negotiated reopening. On 25 September Iran's foreign minister said Tehran had offered to reopen the strait within seven days if the United States lifted its naval blockade of Iranian ports and met other conditions. President Trump rejected the offer the next day. Reuters reported on 30 September that Washington had sent feedback through Qatar; an official briefed on the talks said sequencing was the main sticking point. The Reuters report did not announce an agreement or a reopening.

It is the only way in or out of the Gulf by sea. In normal times ships keep to two lanes, each two nautical miles wide, one in and one out. In 2024 about 20 million barrels of oil a day went through, about a fifth of all the oil the world uses.

35 maverage depth of the Gulf

Now look at the colours of the water. The Gulf behind the strait is shallow: 35 metres deep on average. Stand a fourteen-storey building on the bottom and its top floors would be in the air. Even near the entrance the floor is only about 100 metres down.

Past the strait, the Gulf of Oman drops past 2,000 metres. That is the dark blue. Everything strange in this story follows from the difference.

17%of the Gulf floor dry

Lower the sea by ten metres. A sixth of the Gulf floor is already dry land. The pale line is today's coast; everything green-brown inside it was seabed a moment ago. Bahrain stopped being an island at five metres.

50%of the Gulf floor dry

At 31 metres, half the Gulf is gone. Qatar has become a hill on a plain joined to Arabia, and Bahrain is part of the same plain. What sea is left is a wide arm along the Iranian shore.

80%of the Gulf floor dry

At 60 metres, what is left is a thin arm of sea along the Iranian coast, following the deepest groove in the floor.

−84 mthe sea leaves the Gulf

Once the sea drops below 83 metres, the ocean pulls back out of the Gulf, because the floor of the narrows is higher than that. Only the deepest hollows inside are still lower than the sea; the pale patches mark them. The ocean now stops at the mouth. For the first time in this descent, there is no strait: the Gulf of Oman ends in a beach.

• hollows lower than the sea

20,000years ago

The last ice age. So much water is locked up in ice sheets that the oceans stand 121 metres below today. The Gulf does not exist. In its place: 237,000 square kilometres of dry land.

• land that was seabed
• today's coast
• rivers the ground implies

Let rain fall on this land and run downhill, and the ground draws its own rivers. The blue lines are that: water following the shape of today's seabed.

They gather into one trunk that starts where the Tigris, the Euphrates and the Karun reach the sea today, runs about 1,200 kilometres down the middle of the basin, and leaves through the Strait of Hormuz. The archaeologist Jeffrey Rose calls it the Ur-Schatt, the ancestor of today's Shatt al-Arab. In thirteen cores taken from the Gulf floor, the lowest layer is river silt laid down between 30,000 and 12,000 years ago.

How big is it? Here is Great Britain at the same scale, turned to lie along the valley. The dry floor, at 237,000 square kilometres, is bigger. Rose's own estimate of the land exposed, about 200,000 square kilometres, puts it at roughly the size of Great Britain.

• Great Britain, same scale

Put today's cities on it. Kuwait City is about 1,000 kilometres from the open sea as the crow flies. Doha is 500 kilometres away, Dubai 120. You could walk from Iran to Qatar with rivers to cross, but no sea.

At the strait itself, the river runs out through a valley where the tankers now sail. Just past the narrows the floor drops into a hollow about 215 metres deep, lower than even the ice-age sea. Lambeck's model lets the late ice-age sea into this hollow; with the river running through it, it could also have been a lake. We found no dated core from it to tell.

• low basin

People lived around this basin long before the ice age peaked. The red dot is Jebel Faya, near today's Sharjah, where stone tools about 125,000 years old were found.

Rose argues that in the driest times the valley, with its river and springs, was a refuge he calls the Gulf Oasis. It is a hypothesis, and not everyone reads the ice age that way: Lambeck writes that it appears to have been cooler and drier than today, with perhaps little chance for lakes to form in the hollows. The floor itself has never been dug: it is under the sea.

• Jebel Faya, stone tools about 125,000 years old

Water may also have come from below. Fresh groundwater still seeps up through the Gulf floor today; a spring off Jubail was still being used in the 1950s. A 2026 study, not yet peer-reviewed, models the areas of the exposed floor where springs could have flowed at the ice-age low: about 13,000 square kilometres on the Arabian side, a figure the authors say could be off by as much as a factor of ten.

Then the ice melts. Around 14,500 years ago the sea jumps: in a few centuries it rises by about 20 metres, a surge known as Meltwater Pulse 1A.

14,000years ago: the strait is back

Around 14,000 years ago, in the middle of that surge as the Barbados corals record it, the rising sea tops the floor of the narrows and pours into the valley. The Strait of Hormuz exists again.

That date is this page's own reading: the moment the coral record of sea level passes the depth of the narrows in today's seabed. It is probably on the late side. The corals grew in the open ocean; in the Gulf the sea stood somewhat higher, and the geophysicist Kurt Lambeck's model of the Gulf opens a narrow waterway at Hormuz earlier, around 17,000 years ago once his radiocarbon dates are turned into calendar years.

By 9,400 years ago half the floor is under water again. On flat ground a small rise moves the coast a long way: Rose cites models in which the shoreline advanced a kilometre a year or more in places. Three dated cores show the sea arriving in the western Gulf from about 11,500 years ago and the water turning fully marine around 8,800.

Lambeck's model has the sea reaching roughly today's coast around 7,000 years ago; the coral record, which this map follows, is still about 7 metres lower then. Between 7,500 and 6,500 years ago, the number of known sites on the Gulf's shores jumps from about ten to more than sixty. The gold dots are some of them. At H3 in Kuwait, from 7,500 to 7,000 years ago, pieces of bitumen have been read as the waterproof coating of boats.

Were these the valley's people, pushed uphill by the water? That is Rose's hypothesis, and the spike in sites fits it. A hypothesis is not an excavation, though, and nobody has dug the drowned floor.

• coastal sites, 7,500–6,000 years ago

Here is the whole return on one chart, from the record this page uses.

Sea level from dated corals: Barbados (Peltier and Fairbanks 2006) up to 8,900 years ago, Tahiti (Bard and others 1996) after that; the dots are the fitted points. These are levels in the open ocean far from the Gulf; in the Gulf itself the ice-age sea stood somewhat higher, because the land there rose and sank differently.

Put the dates in a row. People were using the cave at Lascaux, in France, about 21,000 years ago: that is when the charcoal, bone and antler they left behind date to. At that time there was no Strait of Hormuz. It came back around 14,000 years ago, and the Gulf reached roughly its present shape around 7,000.

The waterway in the September 2026 headlines is younger than the Lascaux occupation, and the Gulf in roughly its present shape is not even twice as old as the pyramids.

The oldest pearl yet found comes from this coast. It lay in the floor of a house on Marawah island, off Abu Dhabi, in layers dated to 5800–5600 BC. On Akab, in the lagoon of Umm al-Quwain, Stone Age fishers left pearls and fish-hooks cut from pearl-oyster shell. The people of the new shore were already working the sea.

• places in the text

By 2300 BC the Gulf was a trade route. Mesopotamian texts name three lands along it: Dilmun, Magan and Meluhha, always in that order or its reverse. Dilmun was centred on Bahrain, whose harbour-capital at Qal'at al-Bahrain is still there; some 11,774 of its burial mounds survive. Magan was the copper country of Oman and the UAE. Meluhha, most scholars say, was the Indus valley.

Sargon of Akkad boasted that their ships moored at the quay of his capital. At Ra's al-Jinz, on Oman's easternmost cape, more than 200 slabs of bitumen that once coated reed boats have been found, barnacles still on the outside. The bitumen came from northern Mesopotamia.

• places in the text
• voyages and routes

In the winter of 325 BC Alexander the Great's admiral, Nearchus, brought his fleet back from India along the Iranian coast. Near the strait his crews saw a long cape across the water, about a day's sail away; local guides said it was Maceta, in Arabia. He beached by the river Anamis, at a place called Harmozeia, by the river most scholars identify with the Minab, and in January 324 BC sailed on past the islands of the strait.

• places in the text
• voyages and routes

For centuries Hormuz stood on the mainland, on a creek of the Minab river. Marco Polo came through around 1272 and called it “a city of immense trade”: sickly, fiercely hot, and full of stitched ships that often sank.

Around 1300, fleeing Mongol raids, its ruler moved the town to a barren island offshore, Jarun, which took the name Hormuz. The island had no fresh water of its own; Ibn Battuta, who came around 1332, saw drinking water carried in on people's backs.

Yet it became the Gulf's great market. Chinese fleets under Zheng He reached it; on the last voyage they lay here from 17 January to 9 March 1433. In 1442 the Persian envoy Abd al-Razzaq Samarqandi found merchants from Egypt and Anatolia to China, Java and Bengal.

In 1507 the Portuguese commander Afonso de Albuquerque attacked. By 1515 Portugal held the island, and its fort on the northern tip controlled the strait for over a century. In 1622 Safavid Persian troops, carried and supported by ships of the English East India Company, took Portugal's fort on Qeshm and besieged Hormuz; the garrison surrendered in April. The trade moved to the mainland port of Gamrun, renamed Bandar Abbas.

At the start of the 19th century the Qawasim were a seafaring clan whose main seat was Ras al-Khaimah, and their kinsmen governed Lingeh on the Persian shore, under Persian suzerainty. One family held ports on both sides of the water that today's maps draw as a frontier.

Britain's East India Company, which traded between the Gulf and India, sent expeditions from Bombay. In November 1809 its force set fire to some 50 vessels and much of Ras al-Khaimah, crossed to the Persian shore to burn Lingeh, and attacked Laft, on Qeshm. In December 1819 a larger force took Ras al-Khaimah.

• events

British records called this shore “the Pirate Coast”. That ships were raided is not in doubt; what the raids were is. The Bombay government called them piracy. In 1986 Sultan bin Muhammad al-Qasimi, a historian, a descendant of the Qawasim and Ruler of Sharjah since 1972, argued that the Company used the charge as a pretext to intervene. In 1997 the historian Charles Davies mostly disagreed with him: the Qawasim were the main raiders, but in an Arabian raiding tradition rather than as pirates in the European sense.

The treaty the chiefs signed in early 1820 wrote its own definition: piracy was killing people and taking goods “without proclamation, avowal, and the order of a government”.

Truces followed. In 1835 the shaikhs agreed to a ban on war at sea during the pearling season; in 1853 the truce was made perpetual. From these truces the coast took its British name: the “Trucial” coast. In 1892 each ruler promised to deal with no power but Britain and to give up territory to no one else; Britain took charge of their foreign relations.

Belonging to the truce decided which shaikhdoms Britain treated as states. Seven of them make up today's United Arab Emirates; Fujairah, which broke away from Sharjah in 1901, was the last Britain recognised, in 1952.

Lower the sea once more, by 16 metres, to where it stood about 7,700 years ago. Among the ground that rises out of the water are the Gulf's pearl banks: the dots are six whose positions a Royal Navy officer fixed in 1906, and at this level four of them are dry ground (one, Halul, is an island even today).

In the bay between Qatar and Abu Dhabi, divers worked mostly on knolls 5.5 to 16.5 metres down. Lambeck's model of the Gulf has the Great Pearl Bank, a shallow ridge between Qatar and Abu Dhabi, among the last ground the returning sea covered.

• pearl banks, positions fixed in 1906

By 1907 pearling was the Gulf's great industry. The British official J. G. Lorimer counted some 4,500 boats and over 74,000 men on the banks; the pearls exported in 1905–06 were worth at least £1,434,399. The Great Diving began in mid-May and lasted about 130 days. A diver usually stayed down 40 to 75 seconds, and 15 metres was an ordinary depth.

Then Japanese cultured pearls, on sale from 1916, and the crash of 1929 broke the trade. In the 1930s Doha's population fell from 27,000 to 16,000. Bahrain's pearling path, from the old oyster beds to the merchants' houses of Muharraq, is now a UNESCO site.

Some of the pearl divers were enslaved: Lorimer notes slaves sold in Hasa and taken to Qatar to dive. Enslaved East Africans were shipped from Zanzibar, about 4,000 km and 16 to 35 days by the monsoon, to Sur on the Omani coast, and from there to the Batinah coast, overland to the Trucial coast, and by sea into the Gulf.

By the 1890s Sur was the main landing place: about 300 people a year in 1894, about 1,000, by local report, in the season before June 1900, many in boats under the French flag. Not all were African: of 95 people the British freed at Muscat in 1904–05, 60 were Persians or Baluchis taken from Makran.

• places in the text
• voyages and routes

Britain moved against the trade slowly and narrowly. Article 9 of the 1820 treaty called carrying off slaves “plunder and piracy”, but it was read as banning kidnapping only. Agreements in 1838, 1839, 1847 and 1856 widened the ban step by step; in 1873 the Sultan of Muscat banned all imports and Zanzibar agreed to close its public markets.

Around 1905 British officials counted about 4,000 Africans in Kuwait town, two-thirds of them enslaved, and some 4,000 slaves living apart from their masters in Qatar's towns. Those who reached a British agency could ask to be freed; the historian Jerzy Zdanowski counts 960 people, 288 of them women, freed at the Gulf agencies between 1921 and 1949. The bans came late, and the first ones covered only the trade: Bahrain banned the slave trade in 1937 and Kuwait in 1949. Slavery itself was abolished in Qatar in 1952, in Saudi Arabia in 1962 and in Oman in 1970.

On 26 May 1908 drillers working a concession the Shah had granted to William Knox D'Arcy struck oil at Masjed Soleyman, in the hills north of the Gulf: the first commercial oil strike in the Middle East. Bahrain followed in 1932, the first on the Arab side; Saudi Arabia's Dammam No. 7 in 1938. Abu Dhabi's first field, in 1958, was out at sea, at Umm Shaif. Kharg Island became Iran's great export terminal.

With oil underground, lines on the map began to matter. At Uqair, on 2 December 1922, the British High Commissioner Sir Percy Cox settled the borders between Najd, Iraq and Kuwait, leaving two neutral zones; the Kuwaiti one was split in 1965 with its oil still shared, the Iraqi one in 1981.

In 1952 Saudi guards occupied Hamasa, a village of the Buraimi oasis claimed by Abu Dhabi and Muscat. After arbitration in Geneva broke down, forces of Abu Dhabi and Muscat, backed by the Trucial Oman Levies, retook the oasis in October 1955. The 1974 Treaty of Jeddah settled the quarrel on paper, but the UAE has disputed its text since 1975 and has never ratified it.

• places in the text
• today's land borders

Most of it left by sea, and the sea has one way out. In 1968 the body now called the International Maritime Organization adopted the lanes ships followed through the strait until this year, proposed by Iran and Oman: one lane in, one lane out, with a buffer between. In 2024 about 20 million barrels of oil a day went through, a fifth of the world's consumption.

In January 1968 Britain announced it would pull its forces out of the Gulf by the end of 1971. On 30 November 1971 Iranian troops landed on Greater and Lesser Tunb, which Ras al-Khaimah claimed, and on part of Abu Musa, under a memorandum with Sharjah in which neither side gave up its claim. Two days later, on 2 December, six Trucial States proclaimed the United Arab Emirates; Ras al-Khaimah joined in February 1972.

The quarrel is older: in 1904 a Belgian officer of the Persian customs raised Persian flags on Abu Musa and Tunb, and they came down after British protests. Today the UAE calls the islands occupied, and Iran says they are Iranian.

• events
• today's land borders

Earlier in 1971 Bahrain, on 15 August, and Qatar, on 3 September, had become independent. Iran had long claimed Bahrain; in 1970 a UN envoy reported that the “overwhelming majority” of Bahrainis wanted a fully independent state, and on 11 May 1970 the Security Council endorsed his finding. The dotted lines are today's land borders.

The sea was divided too. Between 1958 and 1974 the states drew lines across the seabed, point by point, to split its oil and gas: Bahrain and Saudi Arabia in 1958, Iran and Saudi Arabia in 1968 (Farsi island to Iran, Arabi to Saudi Arabia), Iran and Qatar in 1969, Iran and Bahrain in 1971, Iran and the UAE, for Dubai, in 1974. The lines here join the turning points in the treaty texts with straight segments.

The Iran–Qatar line crosses the world's largest non-associated gas field: North Field on the Qatari side, South Pars on the Iranian. QatarEnergy puts North Field's recoverable gas at 900 trillion cubic feet.

• voyages and routes
• today's land borders

And through the strait itself: on 25 July 1974 Iran and Oman signed the line that splits its seabed, 124.85 nautical miles and 22 turning points from the Gulf to the Gulf of Oman. Where the treaty bends the line in an arc round Larak island's 12-mile sea, the map joins the points straight.

In September 1980 Iraq declared void the 1975 Algiers agreement, which had run its river border with Iran along the deepest channel of the Shatt al-Arab, and invaded Iran. During the eight-year war that followed, both sides attacked merchant ships in the Gulf: tallies run from about 340 to about 450 attacks, depending on who counted. From July 1987 the US Navy escorted Kuwaiti tankers re-registered under the American flag. On 18 April 1988, four days after a US frigate struck a mine, American forces destroyed Iran's Salman and Nasr oil platforms and sank an Iranian frigate and a patrol boat.

• events

On 3 July 1988 the US cruiser Vincennes shot down Iran Air Flight 655, an airliner climbing inside its assigned corridor out of Bandar Abbas. All 290 people aboard, from six countries, died. The red dot marks where the wreckage fell, 6.5 miles east of Hengam island, beside the lanes. In 1996 the United States and Iran settled Iran's case at the International Court of Justice.

On 2 August 1990 Iraq invaded Kuwait; the Security Council met the same day. In January 1991 Iraqi forces released crude from Kuwait's Sea Island terminal and tankers into the Gulf: NOAA puts the spill at 6 to 8 million barrels, and other estimates run from 2 to 11 million. As they retreated in February, they set fire to between 605 and 732 oil wells, depending on who counted; the last was capped on 6 November 1991. In 1993 the UN fixed the Iraq–Kuwait border, and Iraq accepted it in November 1994.

• events
• today's land borders

Some lines went to court. On 16 March 2001 the International Court of Justice ruled, by twelve votes to five, that the Hawar Islands, which lie just off Qatar's west coast, belong to Bahrain, and unanimously that the ruined town of Zubarah, on Qatar's north-west coast, belongs to Qatar.

In 2019 the strait was a flashpoint again. In May four ships at anchor off Fujairah were damaged; in June two tankers were hit by explosions in the Gulf of Oman, which the US blamed on Iran and Iran denied; in July Iranian forces seized the British-flagged tanker Stena Impero.

Then, after the United States and Israel attacked Iran on 28 February 2026, Iran effectively shut the strait; Iran's president said the Americans closed the routes first. The US Navy blockaded Iran's ports from 13 April. In June, with the usual lanes considered mined, Oman and the IMO opened a temporary corridor through Omani waters: the dashed line. A memorandum the two presidents signed on 17 June collapsed within three weeks.

On 25 September Iran offered to reopen the strait within seven days if the blockade and sanctions were lifted. The next day President Trump rejected the offer.

On 29 September, preliminary Kpler data cited by Reuters put September crude flows through Hormuz at about 9.7 million barrels a day. This records a partial return of exports, not a negotiated reopening; Iran continued to say the strait was closed.

On 30 September, Reuters reported that Iranian foreign minister Abbas Araqchi had received Washington's feedback on the seven-day plan through Qatari mediators. An official briefed on the talks said the main disagreement concerned the order of steps, not the plan's components. The report described talks at that date; it did not announce an agreement or a reopening.

• the 2026 temporary corridor

Kpler data cited by Reuters put September crude flows through Hormuz at about 9.7 million barrels a day. That estimate records a partial recovery in exports; it does not show that the strait has been formally reopened. Under the shipping lanes runs the valley the river cut on its way to the ocean.

UKMTO later published four reports of vessel strikes in the Strait of Hormuz for incidents on 28–29 September. Warning 143, listed as suspicious activity, records a time-late, third-party report of a vessel hit by a suspected projectile on the evening of 28 September; the fire was extinguished, the vessel remained underway and the crew were safe. Three further reports concern incidents on 29 September; UKMTO classified those warnings as “Attack” and marked their sources “Verified”. The warnings do not identify who fired the projectiles or give a full damage assessment. The Kpler estimate above measures crude flows; these reports describe maritime-security incidents.

A river valley for tens of thousands of years. A strait for about 14,000. Pearl banks, a kingdom, a “Pirate Coast”, a truce coast and a tanker route in the last eight thousand. The next time it fills your screen, look at the water and see all of it.