These photos are from Costa Rica's national daily newspaper, La Nación.
The eruptions began around 10 AM and continued into the afternoon. Ash and gas columns spread more than 1 km into the sky, bringing partial darkness to the immediate area. It’s estimated that at least twenty pyroclastic flows – avalanches of hot gas, rocks and ash – occurred on this single day. It was the most dramatic eruption since 1968.
The Miravalles-Arenal Seismological and Volcanological Observatory (OSIVAM) and the National Seismological Network (RSN) collected seismic data for several months leading up to the event. Their instruments detected an increase in the tremor signals several hours before the first outburst.
Unfortunately, several people were killed during the explosions. Two U.S. tourists were hiking with their guide – a man named Ignacio Protti – along the north side of Arenal when the avalanches occurred. A pyroclastic flow emerged from the crater and rushed toward them at a rate of 50 miles (80 km) per hour. Protti was able to save the hikers, although all three suffered serious third-degree burns. Protti and one of the tourists died several days later.
Incredibly, an airplane crashed into Arenal three days later on August 26. The ten people in the plane – eight passengers and two pilots – all died. Two months later another plane crashed into the side of Arenal. Both planes are believed to have deviated from their flight routes to get a better view of the eruptions. The debris from the crashes can still be seen today from the Los Lagos Hotel.
Rest assured, travelers: all hotels in the Arenal area are set at a safe distance of the volcano, although hiking beyond the posted warning signs is extremely dangerous. What’s more, Arenal entered into a resting phase in 2010—for the time being there is virtually no danger of being affected by an eruption.