Gaya APA

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

Gaya MLA

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