First read this:
California is volcano country – Magma Cum Laude
Yes Magma Cum Laude is the name of the American Geophysical Union’s volcano blog, no joke. Though punny.
For this post they decided to highlight this new report by the USGS focusing on the volcanoes of California and the threat they pose. For your reading pleasure here is a very readable report from a government agency: https://pubs.usgs.gov/sir/2018/5…
This is good stuff especially if you like looking into hazards and volcanoes are one of those things we have many of in the US, and our neighbors have more than a few as well, but an eruption is something that never really happens here. Unless we are talking about Hawaii, or Mt St Helen’s in 1980. But the threat exists and should not be taken lightly. And I want to take advantage of this report to show why there is more to geography than maps, and that maps are only one part of the whole.
Now Volcano’s are very spatial objects: their area of effect varies based on if it is an explosive eruption like Mount St. Helen’s or effusive one like Mauna Loa.* And there are many stripes in between depending on the dissolved gas content in the lava, if there is groundwater around, or the mineral composition of the lava.
But Volcanos are only found in 4 places in the US as an active threat: The West coast due to the subduction zone, Alaska for the same reason, Yellowstone which is a hot spot due to the now disappeared Fallaron plate, and Hawai’i due to a wandering hot spot that you can see in bathymetry:
Yes the Hawai’ian Islands are merely the last in a long line of sea mounts going all the way back to the Aleutians thanks to a more or less stationary hot spot. So for 81 million years a series of volcanoes have slowly grew up and faded away in the middle of the Pacific of which the parts we know are mostly only the most recent bits left above water.
Back to California.
Now the report is very good geography, as expected from the USGS. And it does a very good job of nesting contexts with the issues here. For example this map.
This map lists the eight major volcanoes with a moderate to very high chance of erupting in the near future. If you know your California geography you can see these are generally not that close to any major urban area but rather close to several minor ones, infrastructure, and transport corridors. And as the map notes Volcanoes are spatial hazards due to the variety of threats they pose but that no one volcano offers all threats to deal with. For example Mt Shasta, the only Stratovolcano among the ones listed, will produce ashfall and flooding along with pyrocastic flows and ballistics. By comparison the Salton Buttes will not produce much in the way of ashfall but could be a source a variety of near vent hazards like Shasta will produce.
But let’s now layer some geographies:
So this set of maps, not a small multiple, shows the population density in the vicinity of these volcanos. Why the Coso volcanic field is not shown is not known but it is located inside the China Lake Naval Air Weapons Station. Now we see some population densities that give us a hint to how many people live there but people are not stationary, they’re mobile. So when we consider movement what would the largest threat areas?
Did you guess Mt Shasta?
No? That’s ok, there is no test at the end of this. But why is Shasta so high? what feature makes that skew that direction. Look a the map above for a clue.
I-5 passes by the foot of this volcano and has about 1500 vehicles on it per hour.
There are many other aspects the report goes into but the last I want to touch on is a structural one: Who owns the land these volcanoes are situated upon?
So why is this important? Jurisdiction and response. So if the Ubehebe craters go up contacting state agencies is good since they should know but the appropriate federal agency is the one actually who needs to be contacts so that level of response can be activated. Now in all likelihood all information should get everywhere but one should not take that chance if needed. Plus these values are modified but what form of government and private agency is the specific owner of some swath of land.
Especially the semi autonomous nature of tribal lands means an emergency response may need to be locally approved before state and federal assets can move into that area. The exigencies of the emergency will modify that as well.
I touched on these two aspects of the whole as a way to highlight various geographies. We have natural hazards, Human-nature interfaces, and governmental jurisdictions in just what is shown by me. The report goes a bit further.
But for what we have, it’s very illuminating. Sure there are piles of maps as tools of description but there are also tables and charts that provide context and detail to those maps because the map is not the end state but one part of the report among many. And a the maps don’t go into these lovely little bits of detail that show the intensive and pervasive nature of ash rain:
Even a fine dusting of volcanic ash can cause widespread disruption to power lines. For example, although the 2011 Cordón Caulle eruption in Chile was relatively small, an area some 150miles away from the vent was affected by ash fall. In multiple towns, blackouts owing to damage to the electrical infrastructure began within days of the start of the eruption and persisted for weeks. Ash fall caused flashovers (electrical discharges) on insulators and ash accumulation caused poles to collapse. Lightning strikes spawned in the ash clouds damaged substations.
With this one could look as the powerline map and realize the Pacific DC Intertie passes right through the Long Valley volcanic region. With a little additional research we can see this one HVDC line has a:
…capacity is 3,100 megawatts, which is enough to serve two to three million Los Angeles households and represents almost half (48.7%) of the Los Angeles Department of Water and Power (LADWP) electrical system’s peak capacity.
So if a lahar takes out a few transmission lines or ash rain covers a hundred miles of line that could severely affect the ability of the LADWP to get water and electricity to citizens even if the eruption never directly affects the city in any other way. That could be problematic. Especially if the sudden demand shift lead to substation issues like this: Fire, explosion at LADWP facility leaves 94K without power in San Fernando Valley
And the map only hints to that.
Geography is a many level tool that changes with scale, points out hidden features, and can aim the way to the some deeper contexts. Because geography is everywhere and everything is spatial.
*For fun here is a video made from the fist several shots of a photographer who was on site for the Mt Saint Helen’s eruption:
And this is old (1940) film of Mauna Loa erupting, just look at that flow.