Monday, Jan 28, 2013
What seems to be a strong seismic swarm has been visible on recent seismograms, but IGPEN has not issued any notes about this otherwise interesting activity, it is suspected that the VC1 station at the NE base of the volcano is either malfunctioning, showing something else or simply having a very strong magnification of normal backgroud seismicity. [more]
Wednesday, Jan 23, 2013
Another pulse of volcanic earthquakes is in progress under Cotopaxi volcano. Such swarms have been occurring several times recently, but for now, can be considered as part of the normal behavior of an active, but currently dormant volcano. [more]
Cotopaxi volcanoCotopaxi is one of South America's most famous volcanoes and one of its most active ones. With its 5911 m it also ranks among the world's highest active volcanoes (26th highest).
The majestic, snow covered symmetrical stratovolcano is located on the Eastern Cordillera of the Ecuadorian Andes, 60 km south of Quito and 35 km northeast of Latacunga.
Cotopaxi's steep cone has nested summit craters, the outer of which measures 550 x 800 m in diameter.
Cotopaxi erupted more than 50 times since 1738. The most violent historical eruptions of Cotopaxi volcano were in 1744, 1768, 1877, and 1904. its eruptions often produced pyroclastic flows and destructive mud flows (lahars). Some lahars have travelled more than 100 km and reached the Pacific to the west and the Amazon Basin to the east.
At the moment, it has been dormant for over 70 years, which is an unusual long interval in its recent history.
Background:Cotopaxi has often produced lahars during eruptions melting the snow on the upper flanks. The lahars have eroded deep valleys in all directions from the summit of the andesitic volcano. These valleys alternative with large andesitic lava flows that extend as far as the base of the volcano.
The modern stratovolcano was built above the scar left by a major debris avalanche which destroyed an older edifice about 5000 years ago.
A rare high altitude hummingbird (Oreotrochilus chimborazo) has been discovered to live on the slopes of Cotopaxi between 13,000 and 15,000 ft where it nests on protected cliffs.
The last significant eruption of Cotopaxi volcano was in 1907 and produced ash explosions and small pyroclastic flows but no lava flows.
1905 and 1906 eruptions
The eruptions in 1905 and August 1906 consisted in small ash explosions.
A medium-sized eruption (VEI 3) started on 26 Sep 1903 and lasted until December 1904. The eruption occurred from the central vent and produced tall ash plumes, pyroclastic flows and lahars. During explosions on or around 23 October, lightnings were noted by observers, the Times reports the next day: "Since Thursday, electric discharges have been notices on the eastern side of the Andes. Rumblings were heard near the towns this morning, and ashes fell for three-quarters of an hour." (The Times, 25 Oct 1903, "COTOPAXI IN ERUPTION")
1880 vulcanian eruption
One of the largest eruptions of Cotopaxi in historic times began on 3 July 1880. A powerful explosion sent an ash column of 20,000 ft (ca. 6 km) height above the crater in less than a minute.
The British explorer Edward Whymper was climbing Chimborazo at the time of the eruption and reported extremely vivid and strange light and color effects when the large ash plume drifted over him: "... several hours passed before the ash commenced to intervene between the sun and ourselves; and, when it did so, we witnessed effects which simply amazed us. We saw a green sun..." (click to read more) ...more
1877 vulcanian eruption
4 large eruptions occurred at Cotopaxi between January and September 1877. The explosions produced high eruption columns, heavy ash fall, pyroclastic flows and lahars. The eruption caused much damage and there were fatalities.
A 3 day long eruption occurred at Cotopaxi from 13-15 September 1853 and produced ashfall, pyroclastic flows and small lahars.
1768 vulcanian-subplinian eruption
One of the largest historical eruptions of Cotopaxi occurred on 4 April 1768. A large vulcanian explosion took place (VEI 4) and generated a high ash plume, heavy ash fall and pyroclastic flows. Large bombs were falling at great distances. The eruption caused fatalities and extensive damage. ...more
Several small to medium-sized explosions occurred in 1866. Lahars and floods damaged the town of Latacunga and the fallout of coarse pumice west of the volcano destroyed several farms.
A major explosive eruption started in May 1744 at Cotopaxi volcano. It produced extensive ash fall 7-10 cm thick 10 km west of the crater.
2 larger explosive eruptions occurred in December 1742, producing ashfall, pyroclastic flows, and destructive lahars. The eruption caused fatalities.
In 1534 the conquistadors were at war with the locals for control over Ecuador. It is reported that during a battle on the flanks of Cotopaxi, the volcano started an eruption and filled the air with "hot ash" (pyroclastic surges?). The locals viewed the event as a divine sign from their god fled in fear. The Spanish who had no experience with volcanic activity were terrorized and did the same.
A lahar from the 1534 eruption destroyed La Contiega village.
The Chillos Valley Lahar 4500 years ago
The Chillos Valley Lahar from Cotopaxi volcano's north and NE slopes is the largest known debris flow in the northern Andes during the Holocene (11,700 years ago to present).
It descended river systems and flowed 326 km north–northwest to the Pacific Ocean and more than 130 km east into the Amazon basin. The massive avalanche occurred around 4500 years ago.
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