After a hundred years' rest, and an increase in seismicity over three weeks, the Chilean Lonquimay volcano erupted on December 25, 1988 at 4:15 pm.
An eruptive fissure opens 800 meters, at the north-east foot of this small flat-roofed stratovolcano, 3,500 meters from the summit,
- The first phase begins with gas emissions on eight vents distributed over the crack; Rapidly Strombolian activity focuses on two of them, characterized by a plume detected by the NOAA weather satellite extending 70 km to the east at 5,500 m. altitude. On December 27, a viscous lava begins to flow from the crack.
- A second phase begins on December 27 at 18:20: an explosive phreatomagmatic activity ejects a column of gas and tephra which reaches 9,000 meters in five minutes. The activity is concentrated at the upper vent of the crack, which will become the main eruptive center. Two other similar explosions follow each other at an interval of one hour.
On December 28th, the activity is practically continuous, with periods of high and low explosivity, and ejection of spatter, bombs, lapilli, slag and ashes. A cone quickly reaches 50 meters in height and a diameter of 80 meters around the active vent and then develops into open horseshoe down the slope to the northeast.
Activity of Lonquimay during the initial phase: Above, from 25-26.12.1988 - below, in early January 1989 - Courtesy of O. González-Ferrán. / GVP
- Sixty hours after the strong explosion of December 27, the third phase of the eruption begins; it is characterized by a substantial production of lava and a strong magma degassing. The flow of andesitic lava blocks presents two lobes, the longest towards the East. The effusion ratio is 400.000 m³ / day, and a progress of 20-25 meters per hour.
This effusive activity and the degassing continue during the following week; the column of gas and ash remains between 5,000 and 7,000 meters above sea level, and this plume extends for more than 250 km. On January 4th, the plume is capped with a cauliflower in which a thunderstorm develops ... acid rain results.
The explosive activity declines on January 6, before continuing again. On January 8, the block lava flow reaches a length of 3,500 meters.
The Navidad cone, more than 200 meters high in early January, partially collapses on 12 January. Its measurements, on January 21: basal diameter 250 meters, crater 295 meters wide and a cone height of 185 meters.
In April 1989, the Navidad cone is 210 meters high and 700 meters wide.
The fluorinated gases emitted, measured at 300-400 ppm of fluorine over 800 km², have killed hundreds of cattle and horses by fluorosis.
In early July 1989, the authorities began evacuating the 800 inhabitants of the Bernardo Nanco area and 3,800 inhabitants of the city of Lonquimay.
On January 10, 1990, a lava flow was measured at 70 meters / hour emitted by a vent at the NE foot of the Navidad cone.
The eruption ends between January 22nd and 25th, 1990.
It is described as an IEV 3 by the GVP.
Eruption of the cone Navidad / Lonquimay - effusive activity between April and November 1989 - Courtesy of J. Naranjo / GVP
Source: Global Volcanism Program - Lonquimay