Columnar Jointing
14. View north of spectacular columnar joints in andesite of Applegate Peak vitrophyre (unit aa; ca. 210-270 ka) below Wineglass (note geologist at lower right; Panorama H). Columns formed perpendicular to cooling surface as meltwater penetrated solidifying lava along growing fractures (joints) as a result of lava flowing against or beneath glacial ice. Cliff in distance is southeast margin of andesite of Roundtop (unit ar; 15913 ka), also an ice-bounded lava flow.
Photograph by Charles R. Bacon.