‘Pyroclastic rocks‘ or ‘pyroclastics’ are clastic rocks composed solely or primarily of volcanic materials. Where volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed ‘volcaniclastics’. Such rocks abound on the Hawaiian Islands due to these islands, stranded smack-bang in the middle of the Pacific Plate, being overwhelmingly volcanic in origin. Volcaniclastics are superbly exposed at Lanai Lookout, which lies at the base of Koko Crater (see photo above), a 368 m tall, 30,000–35,000 Ma, monogenetic tuff cone that lies east of Honolulu. Although they need a scale, these pictures do not really need words. Or, more to the point, I’m no volcaniclastics expert; I simply think these are beautiful rocks. Enjoy the show.
Featured image at the top of the post is from shows a pyroclastic flow sweeping down the eastern flank of the Soufrière Hills volcano into the Tar River Valley, Montserrat (January 16th 1997). Image and information from: http://volcano.si.edu/learn_galleries.cfm?p=9.