Two years ago, 600 teenagers gathered for a summer camp on the tiny Norwegian island of Utøya.

An annual event organised by the country’s largest political youth organisation, the camp was a perfect opportunity to combine their passion for politics with traditional activities like bonfires, swimming, volleyball and meeting like minds.

These kids should have looked back on their time on Utøya with a smile. Instead their lives, and those of their families, were forever changed by the actions of a lone gunman.

Around 3:30pm on July 22, 2011, eight people were killed and dozens injured when a homemade car bomb detonated at the executive government building in central Oslo.

That same afternoon, 33-year-old Anders Behring Breivik made his way to Utøya where, dressed as a policeman and armed with an automatic rifle and handgun, he opened fire, killing 69 people and injuring over 100 more.

It was the worst peacetime atrocity in Norway's history, and the small nation was overwhelmed with grief in the wake of the tragedy. A survey conducted afterwards estimated that one in four Norwegians knew somebody directly affected by the massacre.

One of the survivors, Emma Martinovic, 18, gave a chilling account of the events of July 22 in a blog post:

I saw one of my friends about to leap into the water, but in a second he was shot. Even at a distance I could see and hear the two shots, straight to the head. I saw his head explode, I saw how he was split apart. Panic spread like wildfire among those on land. I wanted to be among them, urging them to get away, by land or water. I even yelled: "Swim or run!", but nothing helped, there was so much other noise – both the helicopter above us and the bastard's rifle.

Suddenly someone behind me shouts. "Emma, I can't go on."

Now, two years after the shooting, a series of moving portraits titled "One Day in History" depict the profound emotional and physical injuries sustained by survivors.

Andrea Gjestvang was working as a photo editor in Oslo when Breivik's car bomb exploded. After sprinting home to retrieve her equipment, she began photographing the carnage of the attack.

In an email to Slate's David Rosenberg, Gjestvang explains that taking photos helped her process the unthinkable horror taking place before her eyes.

“One part of me wanted to get as far as possible away from the site, as we didn’t know what was going on. Another part of me was desperate to take pictures," she says.

Gjestvang continued to capture the fallout, and decided it was important to explore the experience of those who survived such a catastrophic event.

She began reaching out to the Utøya survivors - more than half of whom were younger than 18. She took photos and listened to their stories about life after July 22.

“For a while it seemed like people in Norway suffered from a kind of ‘22nd of July fatigue,’ but then it is even more important to remind [people] of the fact that the survivors are real people who actually live with this experience every day,” Gjestvang explains to Slate.

Some of the men and women chose not to display their wounds; others wanted to. Some of them describe witnessing the deaths of their close friends and siblings; and the trauma that has remained with them since.

Iselin Rose Borch (pictured), 15, confesses: "In the period after Utøya I had a really hard time sleeping. I was afraid of the dark and suffered from dreadful nightmares. My mum and I decided that getting a dog might help me, so I got Athene. Now she sleeps on top of my stomach every night."

Gjestvang's award-winning photos and the accompanying stories are deeply affecting, but an important symbol of the young survivors' courage and strength.

"My aim is to create a different historical document that can contribute to the public debate, by reminding that terror is not all about politics. It is about the many people who get their lives changed forever,” she says.

You can see the full range of photos from the 'One Day in History' series on Andrea Gjestvang's website. More information available via Slate and the NY Times.