San Juan (volcano)
The volcano San Juan erupted along an approximately four kilometer long eruption fissure in three places on the ridge of the Cumbre Vieja on the Canary island of La Palma between June 24th and July 30th 1949. The three eruption sites were of different volcanological characteristics, the newly formed crater Duraznero , the eruption fissure Llano del Banco and the explosion crater Hoyo Negro .
June 24th is the feast day of Saint John in Spain, who gave the volcano its name. Its geographical allocation is based solely on the names of the three eruption sites.
Course of the volcanic eruption
Over 13 years before the volcanic eruption, a series of earthquakes struck the southern half of La Palma . From February 1949 the earth shook almost every day. The population had no past memories of such events, because the last eruption of the El Charco volcano in 1712 on La Palma was more than 272 years ago.
On June 24, 1949, the newly formed Duraznero crater opened under a violent tremor at around 1800 m above sea level, from which first pyroclastics and then lava emerged, which formed a lava lake at the foot of the crater . Part of the lava flow flowed eastward down the Cumbre Vieja to the municipality of Villa de Mazo .
On the day of the volcanic eruption, forest workers on the mountain reported cracks in the earth from which sulfur gases escaped, and landslides that occurred at the same time as the earthquake, accompanied by intense and long-lasting underground noises.
On July 8, about three kilometers north of the Duraznero crater , about 1300 m, a crevice opened at Llano del Banco , from which large amounts of lava emerged. Local residents reported a strong underground explosion and earthquake at the time. The emerging lava flowed over the steep western slope of the Cumbre Vieja and reached a flow speed of up to 30 km / h. Rocks weighing tons were carried away by the lava. Above Puerto Naos the lava flow assumed a width of 1500 meters and towered up to seven to eight meters.
On July 10, the lava reached the sea, where it formed a lava platform about 6 kilometers long and three and a half kilometers wide, under which various lava tunnels have formed. On this plateau there are now banana plantations, the Faro de Punta Lava lighthouse, built in 1993, and the town of La Bombilla, named after the lighthouse . Between the places Todoque , Las Manchas and Puerto Naos you can see the extensive lava field, which is crossed by the connecting roads between the places.
More than a thousand residents from the affected areas as well as a large number of livestock had to be evacuated in front of the lava flow. Large areas of agricultural land were also lost. Many houses were damaged or destroyed by the violent earthquake. About 300 families lost their homes and their agricultural livelihoods.
On July 12th, the Hoyo Negro crater ("black hole") in the old volcanic cone (1871 m) erupted between the eruption sites Duraznero and Llano del Banco . Accompanied by two violent earthquakes with a violent explosion, the volcano mainly spewed out gases. Observations reported a thick column of black smoke that reached an estimated height of about 3,000 meters. The ash fell in large quantities on El Paso and the surrounding mountains, causing significant damage to agriculture (pastures and banana plantations) and forest fires.
On July 30th, lava emerged again from the Duraznero crater, flowing down the eastern slope at high speed. It covered the connecting roads to the south of the island, destroyed power lines and came to a halt about 300 meters from the coast. The municipality of Fuencaliente , located in the south, was thus separated from the rest of the island for several days in terms of traffic and power supply.
On August 4, 1949, the activity of the San Juan volcano finally ceased.
Flank stability of the Cumbre Vieja
During the seismic activity, an approximately four-kilometer-long system of fissures tore open between the three eruption sites of the San Juan volcano , with the earth sagging up to four meters west of the slope of the Cumbre Vieja . It is not known whether this is a deep or superficial disorder.
To check the flank stability of the Cumbre Vieja, this area has been monitored using eleven ground and one earthquake measuring points since 1994. A ground shift has not yet been determined.
Huge flanks of the volcanoes on the Canary Islands, as well as on La Palma, have occurred repeatedly in history over 100,000 years ago. About 400,000 years ago, the western flank of the Cumbre Nueva collapsed on La Palma , the avalanche of debris was 95 km³.
In 1999, the geologist McGuire published a spectacular tsunami theory, according to which another volcanic eruption on the Cumbre Vieja could break off the western flank of the mountain range and plunge into the sea and cause a huge tsunami . With the publication of the BBC , this theory received wide attention.
This theory was checked by various scientists in the following years and its assumptions were assessed as exaggerated and unrealistic. The danger of a tsunami caused by a spontaneous fall of an enormous earth mass of the Cumbre Vieja of 500 km³ and 100 m / s, as assumed in the theory, appears unrealistic under the geological conditions. A gradual slide of the flank is more likely, which would considerably reduce the danger of the tsunami.
Web links
Individual evidence
- ↑ a b [1] , Rainer Olzem: San Juan eruption 1949 . With historical recordings.
- ^ A b [2] , Global Volcanism Program, Department, of Mineral Sciences, National Museum of History, Smithsonian Institution, 2013.
- ↑ a b c [3] , Juan Carlos Díaz Lorenzo: El volcán de San Juan, 65 años después , August 2, 2014.
- ↑ [4] , R. Urgeles, DG Masson, M. Clanals, AB Watts, T. Le Bas: Recurrent large-scale landsliding on the west flank of La Palma, Canary Islands , Journal of Geophysical Research, Vol. 104, 11 1999 (measurement of the debris avalanche on the western flank of La Palma).
- ↑ [5] , Bill McGuire: Apocalypse: a Natural History of Global Disasters , Cassell, London, 1999.
- ↑ [6] , BBC: Mega-tsunami: Wave of Destruction , October 12, 2000.
- ↑ [7] , Wochenblatt: BBC WANTS TO USE QUOTA POTENTIAL OF DISASTER FORECAST AGAIN .
- ↑ [8] , G. Pararas-Carayannis: EVALUATION OF THE THREAT OF MEGA TSUNAMI GENERATION , 2002.
- ↑ [9] , St. N. Ward and S. Day: Cumbre Vieja Volcano - Potential collapse and tsunami at La Palma, Canary Islands , American Geophysical Union, June 27., 2001
- ↑ [10] , R. Wynn and D. Masson: "Canary Islands Landslides and Tsunami Generation: Can we use Turbidite Deposits to Interpret Landslide Processes?" Southampton, 2003 in Jacques Locat, Jürgen Mienert: Submarine Mass Movements and Their Consequences, 2003 - 540 pages, Kluver Academic Publishers, p. 325.
Coordinates: 28 ° 36 ′ N , 17 ° 51 ′ W