It was promising to be an uncharacteristically warm winter day in Boston. The temperature on 15 January 1919, had soared to 40 degrees from two degrees earlier in the week, prompting many downtown workers to head outdoors.

Shortly after noon in the city's bustling North End, as Model T Fords chugged by and elevated trains screeched above Commercial Street, a group of firefighters sat down for a game of cards in a firehouse near a massive tank that stored molasses used in the production of industrial alcohol.

As the firefighters puzzled over their hands, they heard a strange staccato sound. The rivets on the 50-foot-high storage tank began to shoot off and a dull roar followed. At the noise, firefighter Paddy Driscoll whipped around. "Oh my God!" he exclaimed as he saw the dark torrent spilling out. "Run!"

The Great Molasses Flood was underway. The syrup swamped one of Boston's busiest neighbourhoods, killing 21 and injuring 150.

"Midday turned to darkness as the 2.3 million gallons of molasses engulfed the Boston waterfront like a black tidal wave, 25 feet high and 160 feet wide at the outset," Stephen Puleo recounted in his book "Dark Tide: The Great Boston Molasses Flood of 1919," which vividly captures details of the disaster, including the chilling reactions of Driscoll and others to the tank rupture.

Boston Police patrolman Frank McManus spotted the 26 million-pound wall of goop and shouted to the dispatcher, "Send all available rescue vehicles and personnel immediately - there's a wave of molasses coming down Commercial Street!"

By now travelling at 35 mph, the wave of sugary doom tore through the North End with enough power to crumple small structures, blast a truck through a fence, knock the firehouse off its foundation and rip away a beam supporting the elevated train tracks.

Man wrestles with four legged robot dog at Boston Dynamics lab

Within seconds, two city blocks were inundated - and the death toll began to climb.

City workers who were taking advantage of the warmth to eat lunch outside drowned where they sat. Two 10-year-olds who were collecting firewood near the molasses tank were swept away. Others suffocated as their homes and basements quickly filled.

"I was in bed on the third floor of my house when I heard a deep rumble. ... I awoke in several feet of molasses," Martin Cloughtery told the Boston Globe in 1919. "A pile of wreckage was holding me down, and a little way from me I saw my sister. I struggled out from under the wreckage and pulled my sister towards me and helped her on to a raft. I then began to look for my mother."

Even animals didn't escape.

"A score of Public Works Department horses were either smothered in their stalls by the flood of molasses or so severely injured as their stable collapsed that they were shot by policemen to end their suffering," the Globe wrote in 1919.

"Here and there struggled a form - whether it was animal or human being was impossible to tell," the Boston Post wrote. "Only an upheaval, a thrashing about in the sticky mass, showed where any life was."

World news in pictures Show all 50 1 /50 World news in pictures World news in pictures 14 September 2020 Japan's Prime Minister Shinzo Abe, Chief Cabinet Secretary Yoshihide Suga, former Defense Minister Shigeru Ishiba and former Foreign Minister Fumio Kishida celebrate after Suga was elected as new head of the ruling party at the Liberal Democratic Party's leadership election in Tokyo Reuters World news in pictures 13 September 2020 A man stands behind a burning barricade during the fifth straight day of protests against police brutality in Bogota AFP via Getty World news in pictures 12 September 2020 Police officers block and detain protesters during an opposition rally to protest the official presidential election results in Minsk, Belarus. Daily protests calling for the authoritarian president's resignation are now in their second month AP World news in pictures 11 September 2020 Members of 'Omnium Cultural' celebrate the 20th 'Festa per la llibertat' ('Fiesta for the freedom') to mark the Day of Catalonia in Barcelona. Omnion Cultural fights for the independence of Catalonia EPA World news in pictures 10 September 2020 The Moria refugee camp, two days after Greece's biggest migrant camp, was destroyed by fire. Thousands of asylum seekers on the island of Lesbos are now homeless AFP via Getty World news in pictures 9 September 2020 Pope Francis takes off his face mask as he arrives by car to hold a limited public audience at the San Damaso courtyard in The Vatican AFP via Getty World news in pictures 8 September 2020 A home is engulfed in flames during the "Creek Fire" in the Tollhouse area of California AFP via Getty World news in pictures 7 September 2020 A couple take photos along a sea wall of the waves brought by Typhoon Haishen in the eastern port city of Sokcho AFP via Getty World news in pictures 6 September 2020 Novak Djokovic and a tournament official tends to a linesperson who was struck with a ball by Djokovic during his match against Pablo Carreno Busta at the US Open USA Today Sports/Reuters World news in pictures 5 September 2020 Protesters confront police at the Shrine of Remembrance in Melbourne, Australia, during an anti-lockdown rally AFP via Getty World news in pictures 4 September 2020 A woman looks on from a rooftop as rescue workers dig through the rubble of a damaged building in Beirut. A search began for possible survivors after a scanner detected a pulse one month after the mega-blast at the adjacent port AFP via Getty World news in pictures 3 September 2020 A full moon next to the Virgen del Panecillo statue in Quito, Ecuador EPA World news in pictures 2 September 2020 A Palestinian woman reacts as Israeli forces demolish her animal shed near Hebron in the Israeli-occupied West Bank Reuters World news in pictures 1 September 2020 Students protest against presidential elections results in Minsk TUT.BY/AFP via Getty World news in pictures 31 August 2020 The pack rides during the 3rd stage of the Tour de France between Nice and Sisteron AFP via Getty World news in pictures 30 August 2020 Law enforcement officers block a street during a rally of opposition supporters protesting against presidential election results in Minsk, Belarus Reuters World news in pictures 29 August 2020 A woman holding a placard reading "Stop Censorship - Yes to the Freedom of Expression" shouts in a megaphone during a protest against the mandatory wearing of face masks in Paris. Masks, which were already compulsory on public transport, in enclosed public spaces, and outdoors in Paris in certain high-congestion areas around tourist sites, were made mandatory outdoors citywide on August 28 to fight the rising coronavirus infections AFP via Getty World news in pictures 28 August 2020 Japanese Prime Minister Shinzo Abe bows to the national flag at the start of a press conference at the prime minister official residence in Tokyo. Abe announced he will resign over health problems, in a bombshell development that kicks off a leadership contest in the world's third-largest economy AFP via Getty World news in pictures 27 August 2020 Residents take cover behind a tree trunk from rubber bullets fired by South African Police Service (SAPS) in Eldorado Park, near Johannesburg, during a protest by community members after a 16-year old boy was reported dead AFP via Getty World news in pictures 26 August 2020 People scatter rose petals on a statue of Mother Teresa marking her 110th birth anniversary in Ahmedabad AFP via Getty World news in pictures 25 August 2020 An aerial view shows beach-goers standing on salt formations in the Dead Sea near Ein Bokeq, Israel Reuters World news in pictures 24 August 2020 Health workers use a fingertip pulse oximeter and check the body temperature of a fisherwoman inside the Dharavi slum during a door-to-door Covid-19 coronavirus screening in Mumbai AFP via Getty World news in pictures 23 August 2020 People carry an idol of the Hindu god Ganesh, the deity of prosperity, to immerse it off the coast of the Arabian sea during the Ganesh Chaturthi festival in Mumbai, India Reuters World news in pictures 22 August 2020 Firefighters watch as flames from the LNU Lightning Complex fires approach a home in Napa County, California AP World news in pictures 21 August 2020 Members of the Israeli security forces arrest a Palestinian demonstrator during a rally to protest against Israel's plan to annex parts of the occupied West Bank AFP via Getty World news in pictures 20 August 2020 A man pushes his bicycle through a deserted road after prohibitory orders were imposed by district officials for a week to contain the spread of the Covid-19 in Kathmandu AFP via Getty World news in pictures 19 August 2020 A car burns while parked at a residence in Vacaville, California. Dozens of fires are burning out of control throughout Northern California as fire resources are spread thin AFP via Getty World news in pictures 18 August 2020 Students use their mobile phones as flashlights at an anti-government rally at Mahidol University in Nakhon Pathom. Thailand has seen near-daily protests in recent weeks by students demanding the resignation of Prime Minister Prayut Chan-O-Cha AFP via Getty World news in pictures 17 August 2020 Members of the Kayapo tribe block the BR163 highway during a protest outside Novo Progresso in Para state, Brazil. Indigenous protesters blocked a major transamazonian highway to protest against the lack of governmental support during the COVID-19 novel coronavirus pandemic and illegal deforestation in and around their territories AFP via Getty World news in pictures 16 August 2020 Lightning forks over the San Francisco-Oakland Bay Bridge as a storm passes over Oakland AP World news in pictures 15 August 2020 Belarus opposition supporters gather near the Pushkinskaya metro station where Alexander Taraikovsky, a 34-year-old protester died on August 10, during their protest rally in central Minsk AFP via Getty World news in pictures 14 August 2020 AlphaTauri's driver Daniil Kvyat takes part in the second practice session at the Circuit de Catalunya in Montmelo near Barcelona ahead of the Spanish F1 Grand Prix AFP via Getty World news in pictures 13 August 2020 Soldiers of the Brazilian Armed Forces during a disinfection of the Christ The Redeemer statue at the Corcovado mountain prior to the opening of the touristic attraction in Rio AFP via Getty World news in pictures 12 August 2020 Young elephant bulls tussle playfully on World Elephant Day at the Amboseli National Park in Kenya AFP via Getty World news in pictures 11 August 2020 French Prime Minister Jean Castex is helped by a member of staff to put a protective suit on prior to his visit at the CHU hospital in Montpellier AFP via Getty World news in pictures 10 August 2020 Locals harvest their potatoes as Mount Sinabung spews volcanic ash in Karo, North Sumatra province, Indonesia Antara Foto/Reuters World news in pictures 9 August 2020 Doves fly over the Peace Statue at Nagasaki Peace Park during the memorial ceremony held for the 75th anniversary of the atomic bombing EPA World news in pictures 8 August 2020 Anti-government protesters try to remove concrete wall that installed by security forces to prevent protesters reaching the Parliament square, during a protest against the political elites and the government after this week's deadly explosion in Beirut AP World news in pictures 7 August 2020 A protester throws a stone towards Israeli forces in the village of Turmus Aya, north of Ramallah in the occupied West Bank, following a march by Palestinians against the building of Israeli settlements AFP via Getty World news in pictures 6 August 2020 A woman yells as soldiers block a road for French President Emmanuel Macron's visit the Gemmayzeh neighborhood. The area in Beirut suffered extensive damage from the explosion at the seaport AP World news in pictures 5 August 2020 Damage at the site of Tuesday's blast in Beirut's port area, Lebanon Reuters World news in pictures 4 August 2020 A large explosion in the Lebanese capital Beirut. The blast, which rattled entire buildings and broke glass, was felt in several parts of the city AFP via Getty World news in pictures 3 August 2020 A general view shows the new road bridge in Genoa, Italy ahead of its official inauguration, after it was rebuilt following its collapse on August 14, 2018 which killed 43 people Reuters World news in pictures 2 August 2020 Empty stall spaces are seen hours before a citywide curfew is introduced in Melbourne, Australia EPA World news in pictures 1 August 2020 People take part in a demonstration by the initiative "Querdenken-711" with the slogan "the end of the pandemic - the day of freedom" to protest against the current measurements to curb the spread of COVID-19 in Berlin, Germany AFP via Getty World news in pictures 31 July 2020 Pilgrims circumambulating around the Kaaba, the holiest shrine in the Grand mosque in Mecca. Muslim pilgrims converged today on Saudi Arabia's Mount Arafat for the climax of this year's hajj, the smallest in modern times and a sharp contrast to the massive crowds of previous years Saudi Ministry of Media/AFP World news in pictures 30 July 2020 The Mars 2020 Perseverance mission lifts off at the Kennedy Space Centre in Florida. The mission is part of the USA's largest moon to Mars exploration. Nasa will attempt to establish a sustained human presence on and around the moon by 2028 through their Artemis programme EPA World news in pictures 29 July 2020 A woman refreshes herself in a outdoor pool in summer temperatures in Ehingen, Germany dpa via AP World news in pictures 28 July 2020 Malaysia's former prime minister Najib Razak speaks to the media after he was found guilty in his corruption trial in Kuala Lumpur AFP via Getty World news in pictures 27 July 2020 North Korean leader Kim Jong Un poses for a photograph after conferring commemorative pistols to leading commanding officers of the armed forces on the 67th anniversary of the "Day of Victory in the Great Fatherland Liberation War". Which marks the signing of the Korean War armistice KCNA via Reuters

Scientific American magazine in 2013 explained why a wave of molasses can be much deadlier than a wave of water. "The dense wall of syrup surging from its collapsed tank initially moved fast enough to sweep people up and demolish buildings, only to settle into a more gelatinous state that kept people trapped."

Rescuers and sailors from the USS Nantucket descended on the scene in droves, but struggled in the muck, which stained the waters of Boston Harbor brown for several days.

The search for survivors became a search for answers: Why did the tank rupture and were there signs beforehand?

The second part of that question was easily answered. During the summer of 1918, one of the hottest on record in Boston, North End residents began noticing leaks at the tank. After an employee reported a leak, the company acted - by painting over the grey shell of the tank with a rust-brown colour. "The sticky liquid now blended, chameleon-like, with the fresh coat of paint, indiscernible from the tank's wall," Puleo wrote.

Litigation swiftly followed the explosion, and the lawsuit and trial against the tank's owner, US Industrial Alcohol, would last six years and grow to one of the most exhaustive in the state's history.

The trial produced three theories about the cause of the rupture: structural failure of the tank, fermentation of the molasses that led to an eruption and sabotage via a bomb. The company steadfastly blamed anarchists. A court-appointed auditor disagreed, and in 1925 ruled that the company was to blame for the disaster. US Industrial Alcohol would later pay the flood victims and their families $628,000 - the equivalent of $9.2 million today.

UK news in pictures Show all 50 1 /50 UK news in pictures UK news in pictures 15 September 2020 People enjoying the autumn sunshine as they punt along the River Cam in Cambridge PA UK news in pictures 14 September 2020 Early morning light bathes the skyscrapers of the City of London, at the start of a week in which the UK is expected to bask in temperatures of more than 30 degrees PA UK news in pictures 13 September 2020 England celebrate after they dismissed Australia's Alex Carey to win the second ODI match of the series at Emirates Old Trafford, Manchester PA UK news in pictures 12 September 2020 Protesters outside BBC Broadcasting House in central London, as marches and rallies form across the country calling for a 15% pay rise for NHS workers and an increase in NHS funding PA UK news in pictures 11 September 2020 An empty migrant dinghy floats off the beach at St Margaret's Bay after the occupants landed from France in Dover Getty UK news in pictures 10 September 2020 A view of small boats thought to be used in migrant crossings across the Channel at a storage facility in Dover, Kent PA UK news in pictures 9 September 2020 EU's chief negotiator Michel Barnier, left, arriving from the Eurostar with EU Ambassador to the UK, Portuguese diplomat Joao Vale de Almeida at St Pancras International railway station, London, for the latest round of the negotiations on a free trade deal between the EU and the UK PA UK news in pictures 8 September 2020 Dawn over Coquet Island, a small island off Amble on the Northumberland coast PA UK news in pictures 7 September 2020 A hovercraft arrives to Southsea, Hampshire from the Isle of Wight PA UK news in pictures 6 September 2020 Forensics officers near the scene of multiple reported stabbings in Birmingham Reuters UK news in pictures 5 September 2020 Anti-migrant protesters demonstrate in Dover against immigration and the journeys made by refugees crossing the Channel to Kent PA UK news in pictures 4 September 2020 Activists take part in a demonstration against the HS2 hi-speed rail line outside the Department of Transport AFP via Getty UK news in pictures 3 September 2020 Peter Baker, who plays Trigger in the musical version of Only Fools and Horses, sweeps the stage of the Theatre Royal Haymarket in London, after observing a 15 minute silence to show solidarity with those in the theatre industry that have lost their jobs due to the coronavirus pandemic PA UK news in pictures 2 September 2020 Kadie Lane, right, 11, and Brooke Howourth, 11, hug on their walk to Marden Bridge Middle School in Whitley Bay, Tyne and Wear, for their first day of term, as schools in England reopen to pupils following the coronavirus lockdown PA UK news in pictures 1 September 2020 Extinction Rebellion protesters sitting outside The Houses of Parliament in Westminster, London PA UK news in pictures 31 August Surfers at Long Sands Beach, Tynemouth PA UK news in pictures 30 August Black Lives Matter protesters march through Notting Hill in London in the first Million People March EPA UK news in pictures 29 August A protester reacts as she demonstrates against the lockdown and use of face masks, amid the coronavirus disease outbreak, outside Downing Street in London Reuters UK news in pictures 28 August Caribbean soca dancers display their costumes as they promote the first ever digital Notting Hill Carnival, following the cancellation of the normal Carnival festivities due to the continued spread of the coronavirus disease, in London Reuters UK news in pictures 27 August Father and son team Chris and Sam Milford from historic building conservation specialists WallWalkers begin restoration work on the spire of Norwich Cathedral, which stands at over 312ft high. The first known spire was completed in 1297 PA UK news in pictures 26 August Giant waves at Seaham in County Durham, as the bad weather continues PA UK news in pictures 25 August An assistant at the Wallace Monument cleans the case which houses the William Wallace sword in the Hall of Arms room at the monument near Stirling as they prepare to re-open PA UK news in pictures 24 August Restored World War Two landing craft LCT 7074 is transported from from the Naval Base in Portsmouth to its final resting place at the D-Day Story at Southsea PA UK news in pictures 23 August Jenny Nguyen and Tony Cao, from Vietnam, pose for wedding photos on Tower Bridge in London, as it remains closed to vehicles after it was stuck open on Saturday due to a "mechanical fault". The landmark's Twitter account confirmed only pedestrians and cyclists could use it on Sunday morning PA UK news in pictures 22 August England's Zak Crawley hit 267, joining the exclusive Double Hundred club, on day two of the Third Test match against Pakistan at the Ageas Bowl, Southampton PA UK news in pictures 21 August Harri Teale gathers lavender during the annual harvest on the Wolds Way Lavender farm near Malton in North Yorkshire PA UK news in pictures 20 August Parents and a student react after checking GCSE results at Ark Academy in London Reuters UK news in pictures 19 August Tate Modern workers hold a strike outside the gallery in London, to protest the institution's announcement that it would cut more than 300 jobs from its commercial arm, Tate Enterprises PA UK news in pictures 18 August Two rescued brown bear cubs, Mish (left) and Lucy, cool off in a pool after arriving at their new home with the wildlife conservation charity Wildwood Trust in Herne Bay, Kent. The orphaned pair, who have been living in a temporary home in Belgium since they were found abandoned and alone in a snowdrift in the Albanian mountains, will be acclimatised to their new life in the country before moving to a permanent home PA UK news in pictures 17 August A level students celebrate outside the Department for Education in London after it was confirmed that candidates in England will be given grades estimated by their teachers, rather than by an algorithm. The government U-turn comes just days after Education Secretary Gavin Williamson vowed there would be "no U-turn, no change. PA UK news in pictures 16 August Wasp players take a knee as Northampton Saints stand prior to kick-off in their Premiership match at Franklin's Gardens PA UK news in pictures 15 August Piper Colour Sergeant Lil Bahadur Gurung attends the VJ Day National Remembrance event, held at the National Memorial Arboretum in Staffordshire, Britain Reuters UK news in pictures 14 August People including students hold placards on Whitehall outside Downing Street as they protest against the downgrading of A-level results. The government faced criticism after education officials downgraded more than a third of pupils' final grades in a system devised after the coronavirus pandemic led to cancelled exams yes AFP via Getty UK news in pictures 13 August Benita Stipp (centre) and Mimi Ferguson (left) react as students at Norwich School receive their A-Level results PA UK news in pictures 12 August 2020 A train derailment near Stonehaven has left three people dead. Driver Brett McCullough, conductor Donald Dinnie, and a passenger were killed when the 6.38am Aberdeen to Glasgow Queen Street service crashed amid heavy rain and flooding BBC UK news in pictures 11 August 2020 A woman hydrates in the sun after open water swimming at the West Reservoir Centre in north London Tolga Akmen/AFP via Getty UK news in pictures 10 August 2020 Prime Minister Boris Johnson takes part in an archery session as he visits Premier Education Summer Camp at Sacred Heart of Mary Girls' in Upminster Reuters UK news in pictures 9 August 2020 People cycle through Cambridge as the heatwave continues in Britain EPA UK news in pictures 8 August 2020 Healthcare workers take part in a protest in London over pay conditions in the NHS Getty UK news in pictures 7 August 2020 Emergency services make their way along the seafront on Bournemouth beach in Dorset on one of the hottest days of the year PA UK news in pictures 6 August 2020 Alison Murphy poses for a picture by husband Peter as she walks through a field of sunflowers in Altrincham, Cheshire PA UK news in pictures 5 August 2020 Pakistan's Abid Ali being bowled by England's Jofra Archer during day one of the First Test match at the Emirates Old Trafford, Manchester PA UK news in pictures 4 August 2020 The 'Timbuktu tumblers' from Kenya perform their balancing act on the Southsea waterfront as Zippos Circus reopens in Portsmouth Rex UK news in pictures 3 August 2020 Pelicans interact with a visitor in St James's Park in London PA UK news in pictures 2 August 2020 Lewis Hamilton drives with a puncture towards the finish line to win the Formula One British Grand Prix at Silverstone POOL/AFP via Getty UK news in pictures 1 August 2020 Arsenal's Pierre-Emerick Aubameyang celebrates with the trophy and teammates after winning the FA Cup, as play resumes behind closed doors following the outbreak of the coronavirus disease Pool via Reuters UK news in pictures 31 July 2020 People enjoy the sunny weather at a Bournemouth Beach Reuters UK news in pictures 30 July 2020 An artist puts the finishing touches to a wax figure of Prime Minister Boris Johnson, in the entrance line at Madame Tussaud's in London, as the attraction prepares to reopen to the public following the easing of lockdown restrictions in England PA UK news in pictures 29 July 2020 A member of staff stands on Ai Weiwei's 'History of Bombs' during a photocall for the Chinese artist's new work on display at the Imperial War Museum in London PA UK news in pictures 28 July 2020 Stuart Broad celebrates after taking the wicket of West Indies batsman Kraigg Brathwaite. It was a milestone wicket in his career, reaching his 500th Test Wicket for England. They went on to beat the West Indies in Manchester and therefore win the series 2-1 Getty/ECB

Today, studies have offered grim insight into why the tank collapsed. In a 2015 issue of Civil and Structural Engineer Magazine, engineer Ronald Mayville concluded that the walls of the tank were too thin, a flaw that builders at the time should have known. "No one disputed they under-designed the tank walls," he told the Boston Globe.

Back in the Boston of 1919, the city grieved as more bodies were found, some so battered and glazed by molasses that identification proved difficult. Four months later, the last body attributed to the flood was discovered under the wharf.

"Boston is appalled at the terrible accident," Mayor Andrew J. Peters said in 1919. Over time, however, the Great Molasses Flood has become less of a catalyst for outrage and more of a quirky footnote in history.

"The ﬂood today remains part of the city's folklore, but not its heritage," Puleo wrote. "The substance itself" - molasses - "gives the entire event an unusual, whimsical quality."

But for years after the flood, the memories of it resided not just in North Enders' minds, but in their noses. "The smell of molasses," journalist Edwards Park wrote in 1983, "remained for decades a distinctive, unmistakable atmosphere of Boston."