Often the organics are mixed in with the volcanic sediments. The average organic level is only about three centimeters thick, too thin for a well-developed forest soil. Even a horizontal forest covered horizontally by volcanic ash or mud would, in just a few years, develop stream drainage, but no such topographic relief has been reported. While finer grains predominate, normal grading is clearly present in most, with coarser grains below, fining upward, and it includes inorganic volcanic ash in the sequence. Occasional reverse grading has also been found.
Thin laminations are present, clear indication of deposition by moving fluids.
Time is needed to weather the ash into clay, so the absence of clay implies the lack of much time having passed between layers. As the volcanoes erupted at intervals, mud flows may have inundated a specific area from any one of a number of specific vents. In between the individual eruptions, forests grew on the previous deposit. But as we have seen, this view does not address all the issues. They inter tongue with finer grained ash beds throughout the area.