Why live near a Volcano?

Every now and again I catch up on the news of the world.  Way too often I seem to hear about some small village (or city for Pete's sake) endangered by the eruption of a volcano.  Now, we generally know where these things are (new spouts are naturally not part of this line of thinking).  We know what they can do.  What the fuck, people?
    I couldn't say if many of the folks living around volcanoes go in for the whole, "fiery mountain god" kind of idea, but unless you're sacrificing virgins on a daily basis, I'd imagine you could move a fair distance out for safety's sake.  Go ahead, take a road trip up to the fiery mountain once a quarter.  No need to perch on the slopes or hang in the shadow of.  Ten miles out is close enough.  If the ground quakes, you know you've done something wrong.
    There must be some good reasons for staying.  Why else would you risk fiery death or pyroclastic flow?  "We may have a dozen feet of volcanic ash dropped on us from time to time, but the view is just spectacular!"  It just doesn't scan.  Ah, time to make the research.  

Aden, with Portuguese fleet. in Braun & Hogenberg.1590

To the geology!

Simply put, volcanoes occur in areas of the planet's surface where the underlying hot stuff escapes to the surface.  These can be:

1) subducted plate boundaries, like the Pacific Ocean's "Ring of Fire,"  where oceanic crust is forced down into the hot mantle, melting at depth and forcing its way back to the surface.  

2) spreading centers, like the mid-ocean ridge in the Atlantic, where plates move away from each other, leaving a gap for lava to leak to the surface.  

3) "hot spots," like the Hawaiian Islands (you can visualize the rotation of the plate by the arc of the island chain) create volcanoes emerging from point sources, which have a number of possible explanations (hey, give these guys a break, it's not like you can see this stuff happening).  

Thematically related, though rather different, "mud volcanoes" are a horse of a different color (which you can read more about on the webpage noted below).  Moving on  

The last essential (to this blog post) point of interest, is that the material that erupts from these volcanoes varies in composition, depending on whether it's spitting out pure mantle material (which isn't homogeneous) or melted crust material.  The molten rock will also melt the "country rock" that it passes though, further altering the composition.

oooh rocks!

This might not seem like a benefit to many people, but without these, it's tough to find places to live in the Pacific Ocean (and other bodies of water).  Plenty of landmasses are built entirely out of volcano (see: Islands, Hawaiian).  When they eventually start sinking back into the sea (well, erosion helps) you get your guyots, and later your atolls (which are very handy for nuclear tests).  These are nice places to do some snorkeling and see all the pretty fishies around the reefs.  Atolls can also shelter lagoons and islands, perfect for shipwrecking sailors.
    Volcanoes can also be the high ground in the middle of a relatively flat region.  It's always important to have a good view of the surrounding countryside.  Basalts also make great foundations if you don't want your walls to be undermined.  While most sane people wouldn't build their castles on the top of an active volcano, it's not always possible to know.

Trosky Castle, CZ

you also get Dirt!

Yup, mineral-rich soil seems to be the best reason for tempting fate by living in the shadow of a volcano.  While fresh lava flows and ashfalls are hardy hospitable to growing things, after a fair bit of weathering, it provides quite a fertile home.  Volcanic soils (generally andisols) are very high in Iron, Aluminum, and Silicon, which in this form are easily accessible to plant life.  These soils are well drained, but hold water readily, allowing plants to recolonize quickly after volcanic ashfalls.  

    Depending upon the climate, all kinds of things are grown in volcanic soils.  In the USA, the Pacific Northwest has some pretty damn productive forests sprouting from the stuff.  Tropical areas grow fruit, coffee, and rice as major cash crops.  Italians are still producing wine from grapes harvested on the slopes of Mount Vesuvius.  Tobacco, a notorious soil depleter, is also popularly grown in the stuff.    

Final thoughts...

Mount Vesuvius has had eight major eruptions in the last 17,000 years, which seem like pretty good survival odds for the locals (sorry Pompeii), considering that the soil in southern Italy outside of the Naples region is otherwise very poor (limestone bedrock).  When you have to choose between scratching out a living in the "safe" zone, and living the high life in the shadow of fairly unlikely doom, it seems like an easy choice (until your luck runs out). 

Notes
Cascades geo - tellurianstudies.weebly.com/geology-how-the-cascade-mountains-were-formed.html
Mid Ocean Ridge -oceanexplorer.noaa.gov/explorations/05galapagos/background/mid_ocean_ridge/mid_ocean_ridge.html
Hawaii - sciencedaily.com/releases/2011/06/110629091644.htm
Volcanic soil - volcanology.geol.ucsb.edu/soil.htm
Mud volcano - hvo.wr.usgs.gov/volcanowatch/archive/2005/05_10_13.html

Soils - volcanology.geol.ucsb.edu/soil.htm
Growing things - http://blogs.agu.org/magmacumlaude/2011/02/02/foliage-vs-geology-plants-on-volcanoes/
Mount Vesuvius - geology.com/volcanoes/vesuvius/
Wines on Mt. Etna - http://www.winewordswisdom.com/wine_reviews/mount-etna-wines.html
Ash Fall agricultural effects - http://volcanoes.usgs.gov/ash/agric/
Atolls - education.nationalgeographic.com/encyclopedia/atoll/