In 1917, the port city of Halifax in Nova Scotia was a bustling scene of activity.

TheBoston Common Christmas Treea gift from Nova Scotia to Boston.

Streets were filled with soldiers and sailors and local businesses boomed.

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The citys population swelled to more than 60,000.

SS Imowas late that morning because she had to wait for her coal to arrive.

Minutes later the fumes ignited and the ship was engulfed in an inferno.

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As theMont-Blancburned, Coleman stayed at his post tapping out a message in the final minutes of his life.

His message read: Hold up the train.

Ammunition ship afire in harbour making for Pier 6 and will explode.

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Guess this will be my last message.

The message sent to the stations up the line saved the lives of hundreds.

But only few people understood the seriousness of the situation.

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The blast wave toppled buildings and collapsed roofs and ceiling upon their occupants.

The pressure of the shockwavecrushed internal organsand exploded lungs and eardrums of those standing close to the explosion.

Others were picked up and thrown against buildings and lampposts like rag dolls.

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Map showing the extent of the impact and destruction sparked by the Halifax Explosion of Dec. 6, 1917.

Every building within a 2.6-kilometer radius was destroyed or badly damaged.

Fires from overturned stoves erupted everywhere.

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The explosion displaced all the water around the ship momentarily exposing the harbor floor.

The tsunami obliterated a community of Mi’kmaq First Nation who had lived in the area for generations.

The Halifax explosion released an energy equivalent to 2.9 kiloton of TNT.

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For comparison, the nuclear bomb detonated over Hiroshima was sized at 15 kiloton, only five times stronger.

About 1,600 people died instantly from the Halifax explosion and some 9,000 were injured.

Roughly 400 more died from their injuries in the days that followed.

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A section of Mont Blancs anchor that landed on this park is preserved in this monument.

Boston Mayor James Michael Curley sent a message to the U.S. representative in Halifax hours after the explosion.

I am, awaiting Your Honors kind instruction.

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Curley and Massachusetts Governor Samuel McCall organized a relief effort and asked people to contribute.

Within the first hour, they raised $100,000.

Massachusettss total contribution was at over $750,000.

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A view across the devastated neighbourhood of Richmond in Halifax, Nova Scotia after the Halifax Explosion.

The next year on Christmas, Nova Scotia sent a small token of appreciation to Bostona Christmas tree.

This became a tradition from 1971.

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At places along the highway people gather to cheer and get a glimpse of the tree.

The event attracts tens of thousands of people.

The gifting of the tree is no small commitment for a small province like Nova Scotia.

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Mary Tulle, tourism director for Cape Breton Island, echoes his opinion.

Tulle recalled how her grandmother, living three hours from Halifax, watched the dishes shake during the explosion.

Why do we have to stop saying thank you?

Smoke cloud from the Halifax Explosion, probably taken off McNabs Island.

The Norwegian steamshipImoaground on Dartmouth shore, after the Halifax Explosion.

Wrecked homes in Halifax.

Soldiers standing guard in the midst of the devastation on Kaye Street east of Gottingen Street, Halifax.

House damaged by the Halifax Explosion.

Building destroyed by the Halifax Explosion.

Ruins of Army & Navy Brewery operated by Halifax Breweries Limited at Turtle Grove, Dartmouth.