Sta. Marķa-Santiaguito
First, a view of Santa Marķa from the southeast, showing an ideal composite cone shape. Second, two views of Santiaguito from the south with the scarred southwest flank of Santa Marķa in the background.
The valley in the uppermost diagram is filled with ignimbrites, which are giant pyroclastic flows, usually made of very SiO2-rich pumice. Pumice is frozen magmatic froth, made up of thin glass walls surrounding gas cavities or vesicles. The froth is a lacy network made from silicate glass with few minerals. Inside the network are gas cavities, usually amounting to a high proportion of the volume. Many pumices float until water filters into enough vesicles. They are usually bright white, because of their low Fe content and the large number of tiny vesicles, which scatter and reflect light.
The second photo shows a small eruption plume. It is somewhere in the small vulcanian to strombolian range of eruption types. A fact in favor of vulcanian is that the top of the ash cloud was convecting up a little. A bias in favor of vulcanian is that the magma is a dacite, typically a sticky magma that leads to very explosive eruptions. As often in the real world, observation does not fit well with the defined pigeonholes!
The two middle photos show the scar of the giant 1902 Plinian eruption. Is it a caldera or a crater? Both are collapse features caused by eruptions. Small vents can be explosion craters, which are excavated. The 1902 scar is a small caldera. For our purposes a caldera has a diameter of 2 km or larger, anything smaller is a crater, especially if it is a central vent, e.g. a summit crater. The hole from 1902 is now obscured by the actively growing Santiaguito dome, but its initial dimensions seem to be at least 1.5 by 3 km.