Gaya APA

Survey, U, G. (1981). Volcanic and Seismic Activity at Mount St. Helens April 1981 (April 1981). Washington: University of Washington.

Gaya MLA

Survey, U.S., Geological. "Volcanic and Seismic Activity at Mount St. Helens April 1981". April 1981 Washington: University of Washington, 1981. Text.