This is a view of the floor of the El Chichon caldera. This caldera formed during the very explosive El Chichon eruptions of 1982 and is a few hundred meters deep and about a kilometer wide. The caldera is filled with a shallow acidic lake that has a blue-green color, common to caldera lakes elsewhere. This color is partly due to the huge amount of dissolved minerals in the acidic water, and partly due to lots of fine, light-colored ashy sediment that is continuously stirred up by boiling areas. You can easily see a number of fumaroles around the base of the caldera walls.
This is a view of the El Chichon caldera, formed during the very explosive eruptions of late March and early April of 1982. The caldera is about a kilometer wide and a few hundred meters deep. Prior to the 1982 eruptions the summit of the volcano consisted of a large lava dome within a shallow caldera. There is a shallow acidic lake in the caldera, fed entirely by ground water. You can see that there have been numerous landslides into the caldera.
This is a view of El Chichon from the east. It is not a very imposing volcano. With a summit that is only a few hundred meters above the surrounding area, it is lower than the surrounding non-volcanic hills. In this photo you can see the gullies that have been cut into the 1982 pyroclastic flows. The orange color in the streams is an iron deposit that precipitates out of water that has flowed through the pyroclastic flows.
This photo shows how impressive some of the 1982 El Chichon pyroclastic flows were. Here two volcanologists are examining a tree that was surrounded and killed by the pyroclastic flow. After the tree died, bushes started to grow on the new land surface around the old dead trunk. Most recently, erosion of the pyroclastic flows by a river has exposed much of the lower tree trunk again, giving a good indication of the depth of the pyroclastic flows, which was even deeper than shown here since the base of the tree is still buried.