Volcanic ash layers in deep-sea sediment provide a record of volcanism in oceanic volcanic arcs. Studies of ash layers in marine sediment provide information about eruption frequency, ash thickness, episodes of regional volcanism, and the climatic impact of volcanic eruptions. Ash layers allow correlation of deep-sea cores and provide time markers for the determination of linear sedimentation rates. An obvious advantage to studying ashes in the marine environment subject is the enhanced preservation of ashes as a result of decreased weathering and erosion. One study of North Pacific deep-sea sediment provides a record of episodic explosive volcanism in the Kamchatka-Kurile and Aleutian volcanic arcs over the past five million years. Four hundred and fifty ash layers were examined in North Pacific deep-sea cores from the Ocean Drilling Project Sites 882, 883, and 887, in order to determine eruption frequency and the impact of multiple eruptions on the intensification of Northern Hemisphere Glaciation. Volcanic glass, sampled between visible ash layers, was used as a proxy for sulfate aerosols in the atmosphere. An increase in volcanism is recorded in the sediments just before an increase in glacial sediments and suggests that the observed increase in explosive volcanism may have been the event that triggered the intensification of glaciation. Aeolian mineral grains and volcanic glass can be removed from deep-sea sediments using a chemical extraction technique. Glass can then be separated from terrestrial mineral grains using heavy-liquid separation.