The Azul and Pénjamo rivers on the northern side of Rincón de la Vieja Volcano turned a milky gray over the weekend after days of small eruptions and heavy rainfall washed volcanic material into the waterways. The color change was reported Saturday evening following intense rain around the volcano.
Another moderate eruption occurred at 3:37 a.m. Sunday, releasing steam and volcanic gases for about one minute. No ashfall was reported in nearby communities. The latest activity followed 23 small phreatic eruptions recorded between Monday and Friday. The strongest occurred on July 6 and produced a steam-and-gas plume that rose approximately 200 meters above the crater. Several additional small emissions were detected during the weekend.
Phreatic eruptions are steam-driven explosions that occur when water beneath or inside a volcano is rapidly heated. They do not necessarily involve fresh magma, but they can throw crater-lake sediment, ash and other volcanic material onto the upper slopes.
When heavy rain follows, water carries those loose deposits downhill and into nearby rivers and streams. The sediment can give the water a cloudy gray, white or brown appearance, depending on the amount and type of material being moved. The discoloration does not necessarily mean that a large volcanic mudflow, known as a lahar, has occurred. However, prolonged or intense rain can mobilize accumulated ash, mud and rock, creating faster and more dangerous flows along river channels.
Communities north of the volcano face particular exposure because the Azul and Pénjamo rivers drain areas close to the active crater. Additional eruptions or rainfall could send more sediment into the waterways. Residents, livestock owners and visitors should avoid entering the discolored water or approaching riverbanks while the conditions continue. Volcanic sediment can alter the water’s acidity and may irritate the skin or eyes.
The affected water should not be used for drinking, bathing, livestock or crop irrigation until it returns to normal and authorities confirm that conditions are safe. Pets should also be kept away from the rivers. People near the waterways should move to higher ground if they notice a sudden rise in water level, stronger currents, unusual noises or another rapid change in color. Sediment-rich flows can travel quickly through narrow channels and carry rocks, branches and other debris.
No specific emergency alert had been issued for the two rivers by late Sunday morning. Rincón de la Vieja remains active, however, and further steam-driven eruptions can occur with little warning. Continued rainfall could also carry additional volcanic material from the upper slopes into nearby waterways.
