National Geographic : 1944 Nov
Every Few Minutes Izalco Volcano Takes a 1,000-foot Puff on Its Concealed Pipe The vent of, the crater may be concealed under lava debris. Approximately every eight minutes, a column of gas, dust, and small fragments explodes. Lava issues almost continually from a small side crater (at head of black streak in upper pictures). These air views of a single eruption were made about three seconds apart (601).