This spectacular image comes courtesy of Halldor Sigurdsson at Iceland banking crisis news and more, who has been providing some nice coverage of the ongoing eruption at Eyjafjallajokull (you may be sure that I didn't spell that from memory). More pictures and a nice aerial video can be found here. Note the cars parked at the edge of the lava flow. Yeah, I know most people run away from volcanic eruptions, but geologists and I guess Icelanders aren't most people! Erik at Eruptions has a nice rundown of recent activity.
Iceland is a volcanic wonderland, with the activity resulting from the country's location on the Mid-Atlantic Ridge (a divergent plate boundary), and possible location on top of a hot spot, perhaps similar to the one that underlies Hawaii. The precise nature of the conditions resulting in the volcanism is a concern of ongoing research.
So why can't we see this kind of thing in California? Well, actually we potentially could, but not for the same reasons. California does in part sit astride a divergent (or potentially divergent) boundary in a number of places. The Salton Sea and Imperial Valley area, for instance, sits in a deep trough caused by the rifting of Baja California. A few small volcanoes can be found near the lakeshore. The Basin and Range and Mojave Desert provinces in the eastern part of the state have also been rifted apart, and contain dozens of fairly recent cinder cones and lava flows. The northern Coast Ranges have a number of potentially active volcanoes in the Clear Lakes/Geysers region. And as I discussed in detail in the Other California series, the Cascades and Modoc Plateau provinces are both rich with recent volcanic activity due in part to the presence of the Cascadia subduction zone offshore to the west.
In short, our volcanoes don't erupt nearly as often as those in Iceland (39 times last century), but we do have lots of potential for future geological excitement. I would just love to see a modest eruption somewhere in the state, in one of remote spots anyway. Mt. Shasta and the Long Valley caldera are two places that I prefer would remain quiet...