Pacific coast outcrops on Unalaska Island, eastern Aleutians. Merry Cai (Lamont) provides the scale. The rocks in the lower outcrop behind Merry are pillow lavas. The mottled appearance is produced by the reddish-brown pillow interiors, surrounded by green, inter-pillow sediment and altered pillow rinds. The upper part of the outcrop is an andesite sill with short, columnar joints at 90° to the horizontal contact. These rocks were formed prior to affects of crustal thickening by magmatism and accretionary tectonics, which eventually lead to the emergence of the large islands that we see in the eastern Aleutians today. Photo credit: Gene Yogodzinski (University of South Carolina)