Guatemala's Santiaguito continues to produce strong explosions; May 19, 2016 at 9:34 and 9:56, they were accompanied by a plume of gray ash amount to 4,500 meters asl, and pyroclastic flows on the southern flanks.
Of note, a pileus cloud type formed at the top of the volcanic plume, witnessed the high speed training, then was pierced by it.
Santiaguito eruption 19/05/2016 - formation of the plume wearing a pileus (see halfway up on the top photo) - Photo Gio11Lopez
At Fuego, the eruption of May 18 generated pyroclastic flows "type Boiling over", according INSIVUMEH.
This phenomenon is caused by a magma reboiling and a tangential outlet of abundant quantities of volcanic material and pyroclastic flows, without explosion.
Both volcanoes remain under close monotoring : considering the rains season already present , lahars are likely to form in the evening or during the night.
Sources: INSIVUMEH & Conred