Even though this is superior to anecdotal reports of increasing volcanism, even a century is way too shy a comparison sample to judge whether volcanic eruptions are increasing in frequency, let alone intensity.
Without becoming pedantic about immense geologic timescales, a researcher does not have to look very far back into the relatively recent past, 10 to 15 millennia say, to sample evidence of the frequency and intensity of before and after the Younger Dryas, c 12,500 BC, to find a very intense and frequently "dynamic lithosphere."
But that alone does not rule out the notion that volcanism is on the rise, it actually hints volcanism could really be on the up-swing, here and there, and our perception of such a possibility might not simply be an artifact of greater population density and wider light-speed communications and detection capacity. This is true because we know it's happened before. The noise level in our human-surround is very distracting, especially when we train ourselves to hesitate to react.
Let's see the amount of earthquakes 7.0 and above from 1973 to 2006.
On geologic scale this is hardly nothing but we do see a bit of a trend within our lifetimes. But looking a little futher back...
DATES FROM & TO PERIOD NO. EARTHQUAKES (Mag. > 6.99) --------------------------- ----------- ------------------------------
1863 to 1900 incl 38 yrs :12
1901 to 1938 incl 38 yrs :53
1939 to 1976 incl 38 yrs :71
1977 to 2014 incl * 38 yrs :164 (to Mar. 2011) predict >190 in total.
* Although periods are shown up to 2014, this report was initially written in 2006. Therefore the final period (from 1977) will be updated as required until the end of 2014. In the meantime a predicted total is shown. The earthquake (OFF EAST COAST OF HONSHU, JAPAN) - incidently one of the largest in recent decades - on 11th March 2011 is the last included in these numbers.
You can find the article
here.