17 March 2017 Last updated at 09:23 GMT
A BBC team and some tourists were on the mountain when the explosion happened.
BBC science reporter Rebecca Morelle described the experience of "Running down a mountain pelted by rocks, dodging burning boulders  and boiling steam."
Mount Etna is one of the most active volcanoes in the world, it's been erupting for the last three weeks.
Mount Etna erupts a few times a year.

The 25-year-old is one of the hottest properties on the transfer market.
Liverpool boss Jurgen Klopp has made his signing a top priority.
The Reds refused to comment on renewed speculation but it is expected they will intensify efforts to reach a deal with both Southampton and the player.
Chelsea and Manchester City have both been heavily linked with the defender, who joined Southampton from Celtic for £13m in September 2015.
But BBC Sport understands Van Dijk wants to move to Anfield in what would be a major coup for Klopp and Liverpool owners Fenway Sports Group, who are willing to spend big after qualification for next season's Champions League.
Liverpool still have to reach an agreement with Southampton - and a demand for a fee well in excess of £50m could mean negotiations will be complicated before any deal nears a conclusion.
Former club Celtic are also understood to have a 10% sell-on agreement.
Van Dijk missed the final five months of the season after sustaining an ankle injury following a challenge by Leicester City's Jamie Vardy in Southampton's 3-0 win at St Mary's on 22 January.
It forced him to miss Southampton's EFL Cup final loss to Manchester United at Wembley.

The shadow health secretary warned that some NHS hospitals were planning to double the number of private patients they treat under new freedoms.
In a speech to Labour's conference, he said the coalition risked destroying the character of the NHS that David Cameron had promised to protect.
Labour has not ruled out all competition to provide NHS services.
In the party's 2010 manifesto, it promised patients the right to go private if they were still waiting for an operation at 18 weeks and an "active role" for the independent sector in treating NHS patients.
By Nick TriggleHealth correspondent, BBC News
The role of the private sector in the NHS is a thorny issue.
Ever since the health service was created it has bought in expertise from outside when necessary.
Today it is estimated about Â£1 in every Â£20 spent on NHS care goes to non-NHS providers.
Some of this pays for charities to help in areas such as cancer and mental health care, while some is handed over to private health firms to carry out knee and hip replacements.
The last 20 years or so has been marked by a desire by politicians from all sides to use the market to make the NHS more efficient.
Labour under Tony Blair expanded this under the patient choice initiative.
That allowed patients to choose  non-emergency hospital treatment from an approved list of providers, including many from the private sector.
This set the wheels in motion for a greater role for private firms in the community sector - one of the issues Andy Burnham is warning about now.
Either way, the genie was out of the bottle long ago.
But the party believes the scale and pace of "marketisation" under the coalition threatens the foundations of the health service.
In particular, Mr Burnham said he feared the new freedom for hospitals to earn 49% of their income from private work would "damage the character and culture" of the NHS and take it closer to an American model.
In his speech, Mr Burnham said: "We can save the NHS without another structural re-organisation.
"I've never had any objection to involving doctors in commissioning. It's the creation of a full-blown market I can't accept. So I don't need new organisations. I will simply ask those I inherit to work differently.
"Not hospital against hospital or doctor against doctor. But working together, putting patients before profits."
The shadow health secretary also called for the NHS and local authorities to work closer together to improve care for the elderly and for "full integration" of health and social care services to be actively considered.
"If we can find a better solution to paying for care, one day we might be able to replace the cruel "dementia taxes" we have at the moment and build a system meeting all of a person's needs - mental, physical, social - rooted in NHS values," he added.
The Mount Etna Volcano in Italy has erupted.
[NEXT_CONCEPT]
Liverpool are poised to win the race to sign Southampton's £50m-rated Netherlands defender Virgil van Dijk after it emerged he wants to move to Anfield if he leaves St Mary's.
[NEXT_CONCEPT]
Andy Burnham has vowed to reverse the "rapid" privatisation of NHS hospitals in England if Labour wins power.