How much volcanic material is produced every year? Here's a few estimates.
Global Production
Global mid-ocean ridge systems (magma and lava):
Andesite and Dacite Volcanoes Augustine (1976):The eruption rates for 14 composite cones ranged from 0.5 km3/1,000 years to 27.5 km3/1,000 years.11.6 m3/sec Usu (1910):3.5 m3/sec Bezymianny (1955-1957): 1.8 m3/sec Santorini (1866-1870): 0.7 m3/sec Mount St. Helens (1980-present): 0.5 m3/sec Colima (1975-1976): 0.05 m3/sec From Table 4.2 of Cas and Wright (1987).
Basaltic Volcanoes
The current eruption rate of basalt at Kilauea is about 0.1 cubic km per
year. That's high relative to the entire volcanic chain which was created
by rates of <0.01 to 0.06 cubic km per year over the last 70 million years.
High rates occurred 18, 48, and 58 million years ago. The lowest rates were
from about 30-36 million years ago.
The eruption rates for the Puu Oo lava fountains ranged from 17 to 367
m3/sec (0.05 to 1.15 cubic km per year).
The Laki and Grimsvotn eruptions (1783-1785) had an average rate of 2,300
m3/sec (7.25 cubic km per year).
Nyamuragira (1901-1977): 0.4 m3/sec. Vesuvio (1750-1900): 1.9 m3/sec. Kilauea (1952-1971): 3.5 m3/sec. Merapi (1890-1992): 0.04 m3/sec. From Table 2 in Siswowidjoyo and others (1995). Monogenetic Volcanic Fields Michoacan-Guanajuato field: 0.8 km3/1,000 years. Area near Paricutin: 1.2 km3/1,000 years.
Hasenaka, T., and Carmichael, I.S.E., 1985, The cinder cones at
Michoacan-Guanajuato, Central Mexico: their age, volume, and distribiution,
and magma discharge rate: Journal of Volcanology and Geothermal Research, v.
25, p. 105-124.
Hasenaka, T., 1994, Size, distribution, and magma output rate for shield
volcanoes of the Michoacan-Guanajuato volcanic field, Central Mexico:
Journal of Volcanology and Geothermal Research, v. 63, p. 13-31.
Parfitt, E.A., Wilson, L., and Neal, C.A., 1995, Factors influencing the
height of Hawaiian lava fountains: implications for the use of fountain
height as an indicator of magma gas content: Bull. Volcanology, v. 57, p.
440-450.
Purbawinata, M.A., Ratdomopurbo, A., Sinulingga, I.K., Sumarti, S., Suharno,
1996, Merapi volcano a guide book: Volcanological Survey of Indonesia,
Bandung, 64 p.
Siswowidjoyo, S., Suryo, I., and Yokoyama, I., 1995, Magma eruption rates of
Merapi volcano, central Java, Indonesia during one century (1890-1992):
Bull. Of Volcanology, v. 55, p. 233-263.
Shaw, H.R., 1987, Uniqueness of volcanic systems: in Decker, R.W., Wright, T.L., and Stauffer, P.H., (eds.), Volcanism in Hawaii, U.S. Geological Survey Professional Paper 1350, v. 1, p. 1357-1394. Thordarson, Th, and Self, S., 1993, The Laki (Skaftar Fires) and Grimsvotn eruptions in 1783-1785: Bull. Of Volcanology, v. 55, p. 233-263.