May 1960 ... a sad anniversary , and a chain of fatal events: the largest earthquake, ever recorded , followed by tsunamis, and a few days after , a volcanic eruption that hit Chile.
Involved the plate tectonics ... the decor is drawn , it remains to analyze the sequence of events .
Earthquakes of May 1960 :
After shaking on May 21 , an earthquake measuring M 9.5 on the MMS scale, called Valdivia earthquake, or Great Chilean earthquake, has struck Chile on May 22, 1960 at 3:11 p.m. local ( 7:11 p.m. GMT). The epicenter is located near Lunaco , 570 km south of Santiago. Valdivia was the most affected city.
The earthquake generated local tsunamis. A wave of 8 m high hit the Chilean coast , mainly between Concepción and Chiloé Island , at 16:20 UTC. Ten minutes later , another wave 10 meters high has occurred. Many coastal villages were affected, such as Tolten , which disappeared. Thousands of people were killed, the range of between 2,230 and 5,700 deaths estimated . Material losses were estimated at 400-800 million dollars ( 2.9 to 5.8 billion, after adjusting for inflation)
The main tsunami that resulted traveled the Pacific and hit Japan , the Aleutian Islands , the Philippines , eastern New Zealand, southeast Australia and devastated Hilo / Island of Hawaii 15 hours after the earthquake. Waves over 10 meters were recorded to 10,000 kilometers from the epicenter.
Soil subsidence destroyed buildings , deepened local rivers , and created wetlands in Rio Cruces and Chorocomayo . All water supply and electricity systems of Valdivia were destroyed. Mudslides engulfed homes, polluted rivers and groundwater.
These earthquakes mark the release of mechanical stress between the subducting Nazca plate beneath the South American plate at the Peru -Chile trench . The rupture zone concerns 800 km long, between Arauco , 37 ° S, and Chiloé Archipelago , 43 ° S. The rupture velocity is estimated at 3.5 km. per second .
The eruption of the Cordon Caulle - May 24.
Thirty-eight hours after the earthquake in Valdivia, a vent located in the rift zone of the Cordon Caulle , near the Puyehue , 240 km . east of the rupture zone , erupts. It is accompanied by the emission of a subplinian plume in fungus above, and fumes émisssions along the crack . The most active centers were initially the Gris crater , followed by Azufral crater . The impact of white pumice recorded at 30-40 km. vent has a thickness of more than 10 cm .
The next phase, of rhyodacite ( 68.9-70.01 % SiO2 ) fissural eruptive type,was little observed , poorly documented by local media , too busy with the consequences of earthquakes. It has fueled a crack 5 5 km long , where 21 vents were identified. It produces lava block and a'a flows.
A third phase , characterized by the emission of rhyodacitic lava is supplied through vents oriented NNW transversely to the main crack ; it ends with an emission of viscous lava obstructing the vents ... explosions continue tp the Gris and Azufral craters, to decline on July 22 .
Between May 24 and July 30 ( end date of the eruption given by GVP ) , a volume equal to 0.25 km ³ DRE ejecta and lava flows were issued. The volcanic explosivity index was set to 3, of the same order as that of the 2011-2012 eruption much more documented.
The flows of the 1960 eruption are pink colors ( Ph.1 pumice ) er red ( Ph.2 lava ) - Doc. Singer et al.
The dynamic stress at the subduction zone and its extension towards the continent may have favored conditions for the reactivation of the system , all facilitated by the presence of silicic magma near the surface.
- Rhyodacitic fissure eruption in Southern Andes (Cordon Caulle; 40.58S) after the 1960 (Mw:9.5) Chilean earthquake: a structural interpretation – by L.E. Lara, J.A.Naranjo, H. Moreno.
- Doc archives NOAA.
- Global Volcanism Program - Puyehue - Cordon Caulle