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Referência Bibliográfica


GASPAR, J. L., FERREIRA, T., COUTINHO, R., QUEIROZ, G., MOTA GOMES, A. (1995) - Preliminary report on the volcanic activity at Fogo island, Cabo Verde (april 11 th -may 18 th). Bull. Global Volcanism Network, vol. 20, n.º 5, maio 1995

Resumo


In a previous report we noticed that on the 11th of April two lava rivers could be observed. One was directed to SW while the other progressed towards Portela village. According to Mota Gomes the Monte Beco lava flow-front stopped on April 12th. However, the main lava river kept moving towards W feeding a 10 meters thick aa lava flow-front that destroyed the wine cooperative of Boca Fonte on the 17th.
 
On the 19th of April, Cabo Verde scientists reported that all the fronts stopped and since than no lava flows were produced from the scoria cone crater. The explosive activity also decreased and the emission of pyroclasts started being discontinuous. By that time a small pit formed near the W flank of the scoria cone and pahoehoe lavas began moving towards W on the top of the first aa lava flows. W of Monte Saia this new lava flows showed a considerable lateral spreading and overrode the north and south margins of the earlier aa flows. On May 10th lavas south of the already destroyed Boca Fonte village attained three houses. During this period fumarolic activity remained intense along the NE-SW main fault and apparently because of the inhalation of volcanic gases some people needed medical assistance. Cases of throat and eyes irritation were reported and some patients felt headache and indisposition. Following a request from the Cabo Verde authorities volcanologists from the Geosciences Department of the Azores University arrived at Fogo Island on the 11th of May to assess public health problems related with the eruption.
 
Until May 14th pahoehoe and toothpaste lava flows continued advancing south of Boca Fonte and towards Portela village while gases rise continuously from the main vents. On May 14th at 4 p.m. the activity increased and a cloud of ashes reached 500 meters high.
 
On the 15th of May measurements made at the end of a lava tube 2 Km W of the main vent showed lava velocities of 2 meters per minute. Ropy pahoehoe lavas formed at this stage. The lava flow-front 10 meters away from the lava tube had velocities of 2 meters per hour. On the same day at 7 p.m. a new set of explosions occurred in the scoria cone crater and at least during 5 hours blocks were ejected 30 meters high falling near the crater rim.
 
Several profiles were made at Chã das Caldeiras on May 16th in order to evaluate the CO2 soil degassing. The work was carried out using GASTEC colorimetric tubes fixed in a probe with 1 meter long. Values obtained 70 centimeters below the ground surface were always below 2%. Ground temperatures changed from 67°C to 115°C inside the SW craters where some explosions took place in the beginning of the eruption. In this section of the main fissure sulfur deposits could be observed but fumarolic activity was already very weak.
 
In the morning of May 17th dense clouds of gases and dusts were released from the scoria cone while all the lava fronts appeared to be stationary. Through the afternoon explosive activity increased and strong explosions gave rise to discontinuous projections of spatter that reached 50 meters high. Due to the explosions some large blocks of the crater wall collapsed and clouds of orange and red dust rise about 100 meters.
 
On May 18th streams of gases flowed down the scoria cone slopes and moved towards SW reaching the caldera wall. People that went to Chã das Caldeiras felt irritation of nose and throat more then 2 Km away from the main vents being impossible to approach without a gas mask. A strong sulfur smell was reported as far as Patim, a village 8 Km SW of the eruptive center.
 
Since the beginning of the eruption lava flows covered about 4.2 Km2 of productive land. The village of Boca Fonte, with a population of 56 persons, was completely destroyed and flow- -fronts are now at a distance of 300 meters from Portela. About 1000 persons still continue sheltered in the army camps of S.Filipe, Patim, Achada Furna e Mosteiros. During this eruption nobody was killed but several persons needed medical assistance. Respiratory problems due to the inhalation of volcanic gases and dust constitute the majority of the observed cases.

Observações


Anexos