 The first layers of the last deposit were alternating belts of light and dark @-@ colored material , and were densely welded . They appear to have been erupted in pulses , and continue for hundreds of meters . Deposition was continuous except for one interruption , which can be seen at proximity to the caldera , where the layers are replaced by thin , nonwelded sheets of lava . Another zone of nonwelded material , about 20 metres ( 66 ft ) and near Cajon Los Calabozos , underwent no erosion , suggesting that activity stopped , then began again . 
