November 21, 1999

 

The following is an update on the Cerro Negro Volcano contributed by Mr. Brittain Hill.

 

There was no eruption at Cerro Negro in November, 1998. While flying up to the Casitas area to evaluate the damage from the large landslide, scientists from INETER observed lots of steam emanating from the Cerro Negro cone and the 1995 lavas. This was erroneously reported as the eruption. When they visited the site the next day, they confirmed that the steam was nothing more than inflitration of the 2+ m of rainfall into the still hot 1995 deposits. There was no seismicity and no new deposits, in 1998. I've spoken with the INETER geologists and visited Cerro Negro in March 1999 and can confirm there were no new deposits on the 1995 falls and lavas.

 

We were at Cerro Negro immediately after the August 5-7 eruption and can confirm that some houses were damaged in Rota by relatively large (M4.9 and 4.2) earthquakes that preceeded the eruption by 4-12 hours. There was, however, no damage from lavas or tephra-falls. Lavas were restricted to within 100 m of the new boccas, which opened adjacent to Christo Rey on the S base of the main cone, and maximum distance for incandescent ballistics were about 300 m. Tephra falls >1-cm-thick were restricted to <2 km of the new vents. We will present this at the Fall AGU Meeting, and show how the eruption was successfully forecast using time-volume relationships.

August 9, 1999

On 6 August, 60 homes were damaged by a rock and lava flow from the Cerro Negro Volcano. 17 homes were destroyed in an earthquake related to the eruption which began on 5 August. Lava and ash are erupting from three new openings in the volcano. Government officials declared a state of maximum alert. Approximately 2,000 people have been evacuated to shelters.

August 6, 1999

On 5 August, the Cerro Negro Volcano erupted. Volcanologists measured lava temperatures of up to 1,500 degrees. The activity originated in four new vents outside of the main crater. Lava fountains rose to 300 m in height. On the evening of 4 August, earthquakes with magnitudes up to 4.8 were felt in all of Northwestern Nicaragua.Civil Defense officers began preparations for an eventual evacuation of nearby villages.

November 6, 1998

The continuing eruption of Cerro Negro has forced the evacuation of the village of Rota. Up to 3500 people in several other villages could be evacuated in the next few days as lava flows continue to move down the north flank of the volcano.

 

November 3, 1998

Cerro Negro volcano began erupting on November 3, just one week after 2,000 people were killed by a mudslide originating from neighboring Casitas Volcano. Lava flows and ash covered about 25% of Cerro Negro's north flank soon after the eruption began. These flows appeared to have reached the base of the volcano. There were no reports of damage or casualties.

 

 

View from 2.3 miles (3.6 km) northwest of Cerro Negro on 3:00 p.m. on November 30, 1995. Column is about 1 mile (1.5 km) high and blown to west-northwest (right) by prevailing strong winds. Ash accumulates in Leon (12 miles (20 km) downwind under cloud) at about 2 mm per day. Diffuse lapilli-fall under proximal cloud to about 3 miles (5 km).

Cerro Negro, a cinder cone, reawakened late in the morning of November 19, 1995. Initial activity was Strombolian in character. Detailed observations began late on November 21. An almost constant fountain of material threw bombs and small amounts of ash 1,000-1,300 feet (300-400 m) above the lip of the crater. Some bombs were very large, measuring several feet (meters) across. A new cone was growing and filling the older crater that was built by an eruption in 1992. A small lava dome was growing adjacent to the new cone. On the morning of November 22, a series of strong explosions ejected material that fell on the lower slopes of the cone. By that evening the new cone had overgrown the side of the 1992 crater and material was spilling down the slope. Slow moving lava flows appeared over the edge of the old crater and material from the front of the flow rolled to the base of the main cone.

 

 

View from 2,000 feet (600 m) south-southeast of main vent on 9:50 a.m. on December 1, 1995, last full day of eruption. Note dense black-to-grey convective ash column and fresh fallout on western (left) sector of cone. South rim is morphology from 1992 eruption; no significant growth in 1995 on south cone sector.

 

The eruption at Cerro Negro continued on November 25 and 26. Observers reported that at times massive bombs were thrown 2,000 feet (600 m) into the air. At others times, strong explosions sent up dense ash clouds. Some ash eruptions lasted several hours. The new cone continued to grow and was about 30-50 m below the summit of the old crater. A lava flow advanced about 1,600 feet (500m) to the west but stopped early in the morning on November 26. An unusual spine-like lava dome jutted out on the northern edge of the crater. The dome was about 300 feet (100m) wide and 100 feet (40m) high. Blocks were continually spalling off the dome. The dome produced three small lava flows that extended to the base of the cone and were advancing slowly. Two flows moved slowly to the north and reached about 0.6 to 1 mile (1 to 1.5 km) from the volcano. Earthquake tremor was recorded during the entire period.

 

 

View from 1 km north-northwest of Cerro Negro on December 3, 1995. 99% of lava in view is new, as are the levees and ramps on the north-northeast (left) sector of the cone flank. The upper contact of the ramps represents the 1992 cone rim. About 150 feet (50 m) of height was added to the cone in 1995, with about 2/3 of the 1992 crater infilled with new scoria and lava. Lavas extend to about 1 mile (1.5 km) north of the north base of cone.

 

On December 4, the Department of Humanitarian Affairs of the United Nations issued a

Situation Report concerning Cerro Negro. They requested international assistance for basic relief supplies and food items. They noted that the eruptions has affected 12,000 people and 6,000 people have been evacuated.

Also on December 4, the Associated Press released a story that Cerro Negro stopped erupting on December 3.

 Information supplied by: http://volcano.und.nodak.edu