Several students of Pacific-area volcanism have suggested that observed temporal variations in the rate, volume, or geochemistry of extrusives may depend in some manner on spreading rates (horizontal plate motions) but have been unable to make specific correlations between the two types of phenomena. Recently determined spreading whole rates in survey areas centered at 6 degrees , 10.5 degrees , 20 degrees , and 31 degrees S along the Nazca-Pacific plate boundary all show similar variations: rates decrease from at least 3.8 m.y. ago to a minimal value during the Jaramillo to Olduvai interval centered about 1.32 m.y. ago, then increase by about 7.5% to their present value of 160 mm/y. Rates from the Juan de Fuca ridge show the same pattern, decreasing to a minimum during Jaramillo to Olduvai time and increasing about 10% since then. This pattern recorded at the spreading centers is reflected in both mid-plate and convergent-boundary volcanism. Volume of material extruded in Hawaii reached maxima 4 to 6 m.y. ago and at present with a minimum at 1.0 to 1.5 m.y. ago. SiO (sub 2) content of Aleutian ash layers at DSDP 178 and volumes of Oregonian and Central American extrusives also show maximum values at present and 4 to 6 m.y. ago. The number of ash layers (eruptive events) near the Aleutian Arc may have increased markedly since a minimum 1.5 or 2.0 m.y. ago, but these counts might be complicated by differential plate motions. These contemporaneous maxima and minima of pan-Pacific volcanic activity strongly supports those who have suggested that volcanic variability is linked to changing plate motions.