I'm always a bit wary of sites which call themselves 'The Extinction Protocol'; but if Hekla is bulging, it needs watching as this one mother of a volcano when it does let rip!

Mayon volcano in Albay Philippines belched out black smoke on May 7, 2013 @ 8AM. It reached about 3 kms high and still rising. No official report yet from PHIVOLCS Legazpi. Unverified reports of a tourist guide killed and 4 tourist climbers injured.

http://www.youtube.com/watch?v=Daz21tMfSRw&feature=youtu.be

Mayon volcano in Albay Philippines belched out black smoke on May 7, 2013 @ 8AM. It reached about 3 kms high and still rising. No official report yet from PHIVOLCS Legazpi. Unverified reports of a tourist guide killed and 4 tourist climbers injured.

http://www.youtube.com/watch?v=Daz21tMfSRw&feature=youtu.be

Is there any data or graph available showing multi-decadal/centennial volcanic activity related to numbers and magnitude?

I haven't yet found exactly what you want, but you may be interested in these,

http://www.eh-resources.org/volcanoes.html,

http://chiefio.wordpress.com/2013/05/06/hekla-ing-egypt/,

http://volcanoes.usgs.gov/hazards/gas/climate.php,

http://en.wikipedia.org/wiki/Timetable_of_major_worldwide_volcanic_eruptions.

Popocatepetl volcano of Mexico is quite active at the moment, producing relatively strong explosions. More details here;

http://www.volcanodiscovery.com/popocatepetl/news/33633/Popocatepetl-volcano-Mexico-explosions-eject-bombs-to-15-km-distance.html.

Plus a video to go with it;

http://www.youtube.com/watch?v=gUy7PsYOK1s.

System upgrade for warning of volcanic eruptions in Iceland - see -

http://www.upi.com/Science_News/2013/05/23/Iceland-upgrading-volcano-eruption-warning-system/UPI-95681369340669/

Copahue volcano on Chile/Argentina border is erupting, prompting evacuation,

http://www.bbc.co.uk/news/world-latin-america-22684322.

Sakurajima volcano of Japan produces a spectacular fireworks display (sorry for faulty cameras),

http://www.youtube.com/watch?v=tDkb32l19SI.

More about Sakurajima here,

http://www.volcanodiscovery.com/sakurajima.html.

Nice explosive eruption on Popocatepetl volcano of Mexico today (17/6/2013),

http://www.youtube.com/watch?v=3ATDHCtaMBs&feature=youtu.be&a.

Nice explosive eruption on Popocatepetl volcano of Mexico today (17/6/2013),

http://www.youtube.com/watch?v=3ATDHCtaMBs&feature=youtu.be&a.

Nice explosive eruption on Popocatepetl volcano of Mexico today (17/6/2013),

http://www.youtube.com/watch?v=3ATDHCtaMBs&feature=youtu.be&a.

I saw that it had erupted earlier but that is a super video clip. Thanks for sharing.

Tungurahua volcano of Equador has produced a strong explosion and pyroclastic flows,

http://earth-of-fire.over-blog.com/pages/tungurahua-strong-explosion-and-pyrolastic-flows--8724538.html.

Mt Rokatenda Volcano in Indonesia erupts,

http://www.abc.net.au/news/2013-08-10/indonesia27s-mount-rokatenda-erupts-on-august-102c-2013/4878454.

Aren't we overdue a really spectacular eruption? A Tambora would be nice

Aren't we overdue a really spectacular eruption? A Tambora would be nice

It would certainly take global warming out of the spotlight for a few years 

In all seriousness though, I think Katla in Iceland may be worth keeping an eye on in the next few years. Mt Pinatubo in 1991 was the last big one, that halted global warming from 1992 - 1994, a VEI 5 volcano or higher usually has enough of an impact global temperatures, be careful what you wish for though......

Aren't we overdue a really spectacular eruption? A Tambora would be nice

Or Toba - for the 15000 who survived this supervolcanic event. Be careful what you wish for!

http://en.wikipedia.org/wiki/Toba_catastrophe_theory

(but, sadly, the historical revisionists have been at work - a 'beautiful theory slain by an ugly fact'.)

Aren't we overdue a really spectacular eruption? A Tambora would be nice

Or Toba - for the 15000 who survived this supervolcanic event. Be careful what you wish for!

http://en.wikipedia.org/wiki/Toba_catastrophe_theory

(but, sadly, the historical revisionists have been at work - a 'beautiful theory slain by an ugly fact'.)

Yes, well Toba would be a tad extreme I grant you. Although we'd likely get a sub-zero CET from it

A nice eruption from Sakurajima volcano of Japan,

http://www.bbc.co.uk/news/world-asia-23751191.

A geyser-like vent has opened up outside Rome Airport. Gases and steam has been seen shooting up 10 maybe 15ft into the air. It is not known yet if it's related to volcanism.

http://www.telegraph.co.uk/news/worldnews/europe/italy/10265372/Volcanic-geyser-erupts-close-to-Rome-airport.html.

The nearest dormant volcano to Rome is Alban Hills, http://en.wikipedia.org/wiki/Alban_Hills.

Potentially interesting.  However, the report seems to play it down as a likely one off event 

 LLTNP 105m asl