Gaya APA

Survey, U, G., Washington, U, O. (1981). Volcanic and Seismic Activity at Mount St. Helens September 1981 (September 1981). Washington: U.S. Geological Survey.

Gaya MLA

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