El Chichón has been sporadically active during the recent Holocene period and in the geological record there are a minimum of 12 eruptions detected during the past ~8000 years; none of which are thought to have been larger than the 1982 eruption (Tilling et al. 1984; Macias et al. 2008). Historically the eruptions seen at El Chichón are a combination of lava dome and phreatomagmatic eruptions; the main hazards from eruptions are ashfall and column collapse causing PDCs (Pyroclastic Density Currents) (Tilling et al. 1984; GVP, 2007; Macias et al. 2008). The eruption which occurred ~600 years ago is thought to have played a part in the downfall of the Mayan civilisation!
The third, largest and final episode of the eruption started at 05:22 on the 4th April with the primary hazard of ashfall, with a few PDCs (Sigurdsson et al. 1984; GVP, 2007). The strongest effect was the large amounts of sulphur which were released into the stratosphere (Robock, 2000) from a max eruption column height of ~29 km. There was little loss of life during this episode. After the eruption, the summit crater and lava dome were destroyed and in its place a new crater around 1 km and 300 m deep was formed within the newly formed crater a lake formed from rainwater (GVP, 2007).
One of the most interesting aspects of the eruption is the formation of the volcanic dam which is shown in the picture above. There were multiple lakes in the area formed in this way, however, the one indicated was formed when PDCs blocked the River Magdalena South-West of the summit crater (GVP, 2007). This dam had a height of 55 m and is thought to have grown to ~5 km in length and contained several million m3 of water before rupturing 2 months after its formation (Macias et al. 2004).
On the 26thMay 1982 the dam ruptured and sent a hot lahar downstream (GVP, 2007). Around 11,000 m3 of water was released for the first hour; the dam was fully drained after a further hour. The lahar eventually reached the Penita Hydroelectric dam, where the only noted death occurred, as well as three injuries caused by the temperature of the lahar (GVP, 2007).
Global Volcanism Program (GVP)
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