Passage II

A lahar is a flow of water-saturated volcanic ash and rock. A lahar deposit, formed once the flow stops, consists of clasts (rocks having diameters ≥ 16 mm) embedded in a matrix (a mixture of particles having diameters ≤ 8 mm).

A sample of a lahar deposit was collected at each of 7 distances from a volcano's crater. For each sample, Figure 1 shows the percent by mass of the clasts by composition, and Figure 2 shows the percent by mass of the matrix by particle size class. For the 7 samples combined, Figure 3 shows the cumulative percent by mass of clasts and matrix particles, or of clasts alone, as diameter decreases.