The extrusion of block lava observed 19-20 February was no longer visible by sunrise on the 21st. Dark gray to black clouds were ejected sporadically that morning, rising as much as 500 m, but ash contents declined in the afternoon, and by 1930 no activity was visible. Only intermittent emission of vapor, sometimes containing a little ash, occurred 22-24 February, with columns reaching a maximum estimated height of slightly more than 1,000 m. Activity declined further, to low but voluminous steaming from vents on the E and SW sides of the summit cinder cone, on 25 February. Mild steaming followed for two days. Slumping on the SE side of the summit cone was first observed on the 27th. After clouds obscured the volcano on 28 February, sporadic ejection of gray steam and ash columns could be seen on 1 March. The columns rose as much as 1,400 m on the lst and more than 2,000 m on the 3rd. The summit showed no activity early on 4 March, after which a period of cloudiness prevented observations until the 9th.

Activity 9-13 March ranged from periods of very mild steaming to emission of ash clouds that rose to a maximum observed height of 1,500 m on the 10th. Significant quantities of ash could be seen falling on Fuego's N and E flanks on 13 March. The slumped area on the summit cone had become a clearly-defined, wedge-shaped fissure by mid-March, extending from near the summit to somewhat less than halfway down the SE side of the cone.

Extrusion of block lava resumed on 17 March, after three days of weak steaming. The flow first became clearly visible after sunset, but probably began at or before daybreak, appearing to originate from the base of the summit cone fissure. Lava moved about 0.5 km down Barranca Honda. Many large blocks tumbled down the canyon. At 1915 on 18 March, an explosion ejected incandescent tephra, including large blocks, to a height of about 500 m. Clouds obscured the volcano on 19, 20, and most of 21 March; continuing lava extrusion was briefly visible on the 21st. Explosive activity on 22 March, the last day of observations reported here, produced ash clouds that rose about 2,500 m, accompanied by spectacular lightning. Fine ash fell on Antigua.

Geological Summary. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: P. Newton, Antigua.