Like a mother holding a baby in her arms, Martha Lucía López carried a small wooden barge with a photograph of her son Sergio Melendro, one of hundreds of children reported missing 40 years ago when a volcanic eruption wiped out an entire town in Colombia: Armero.

Sergio was five years old when he went missing on the night of 13 November 1985, when the Nevado del Ruiz volcano erupted at 5,321 metres above sea level. The lava melted its snow-capped peak and joined the riverbeds, creating a mudslide that raced down the mountains to Armero, a town of 31,800 inhabitants. Approximately 25,000 of them died, making it the deadliest natural disaster in Colombia's recent history.

In Armero, located in the department of Tolima in the centre-west of the country, some walls, façades, kitchen floors and the dome of the church remain standing. The rest disappeared in the mud. Since the tragedy, it has been uninhabited, and in 1986, Pope John Paul II declared it a ‘sacred ground’.

On the night of the tragedy, López and her husband heard strange noises and went out into the streets towards the fire station to ask if anything was wrong. She heard on the news that the volcano was erupting, but believed that it would not affect them as they were about 50 kilometres away. Her son stayed at home asleep.

Once in the streets, they began to feel the river water flowing down the streets. The car they were in overturned, and they got out and tried to run. They took shelter in the crown of a tree and then on the roof of a neighbouring house.

However, their house was destroyed and she heard nothing more from Sergio. Years passed before she found out that her family had made efforts to find him and had some leads: they saw an advertisement with his name at the Colombian Institute of Family Welfare (ICBF), which is responsible for protecting children in the country.

López says that her sister tried to look for him at the institute's headquarters in Bogotá. ‘They never let her in... they asked her to bring clothes and photos proving that they were family, nothing else.’

Years later, a friend of López's told her that in New Orleans, United States, a man approached her and told her that her brother had adopted a child who was a victim of the Armero tragedy. ‘He showed her a photo... Sergio's eyes were unmistakable,’ she says, referring to their blue colour. However, they were unable to contact him again.

Ancizar Giraldo, who was 12 years old when the volcano erupted, also provides clues as to what happened.

‘They began to classify them by age; children between 0 and 2 years old, who hardly remember anything, were separated and most of them never reappeared. Children between 5 and 10 years old were taken in by Bienestar (ICBF) and those over 10 years old were handed over to some villages,’ Giraldo told the AP.

He is referring to a social centre, a kind of foster home for children from Armero that was financed with international aid from sponsors who ‘adopted’ the children from afar by sending money for their upkeep. He spent almost four years there, until his mother found him through the photographs published by the ICBF.