We examined the impact of the 5 & 9 most major volcanic eruptions on global sea level. We construct a record of sea level and its uncertainty since 1854. From this we isolate the volcanic signature which surprisingly behaves very differently than models predict.
The mechanism that explains the result is:
Less evaporation leads to less precipitation and hence less water in terrestrial reservoirs and less river discharge.
This influences sea level in two ways:
The water cycle disturbance causes an ‘immediate’ rise in sea level which is then followed by the drop due to ocean densification. It is the only the drop that has been modeled in the past, and no other sea level reconstruction is accurate enough to show either drop or rise in the volcanic signature.
Reference: Grinsted, A., J. C. Moore, S. Jevrejeva (2007) Observational evidence for volcanic impact on sea level and the global water cycle. PNAS, 104, 19730-19734. pdf