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  The Chatter Box : Travel
Why do deserts like volcanos? by Kbee on 25 April 2003 2:50am
I took a trip through the Mohave about a year ago; fell in love with the place. (That a) it was spring, and b) my car's reliable probably had a lot to do with that.) I left home hoping to see *one* volcano (Amboy Crater). Come to find out the place from California through New Mexico is just one big humongous caldera, and the "volcanoes" of various sizes number in the hundreds. Cool.

So, I'm watching poor Mr. Gilliam ("Lost in La Mancha"), standing in the middle of a wash in Spain, wondering if the camera cases are watertight, and, pulling out a map, I find out they got volcanoes in La Mancha, too.

And, last Sahara episode, more volcanoes. Still cool, but what gives? Is there some geographical, weatherish reason that (small) volcanoes/cones and deserts seem to go together?

Pray, enlighten me, oh geo/pyro/sandy folk!
Re: Why do deserts like volcanos? by sleepydumpling on 25 April 2003 9:28am
Kbee - we need a geologist on the site to answer this question. Anyone out there who can help?

Is it because volcanic activity often occurs deep inland on major continents? Are most volcanoes in deserts extinct? It seems places with live volcanoes seem to be quite lush, but those that are extinct have desert surrounding them.

Can anyone add some insight to this question?

Re: Why do deserts like volcanos? by ilse on 28 April 2003 2:52pm
live volcanos often have lots of stuff growing on and around them because volcanic soil is very fertile. as for extinct ones........i don't know, maybe because seismic activity causes mountains and major mountain ranges can affect weather patterns? i'm grasping at straws here. i'm with you, kath, we should definitely have a resident geologist here. or a meteorologist. or a vulcanologist. heck, any kind of -ologist! : )
Re: Why do deserts like volcanos? by Kbee on 28 April 2003 8:24pm
"That morning, Reggie the proctologist wondered why he suddenly had all sorts of strange e-mails about volcanoes."

Meanwhile, the quest continues. (I suspect a lot of my questions could be answered by a good Geology 1A class, but I'm on my own at this point.)

OK, so, the Red Sea is actually a very visible fault line (kind of like Tomales Bay is the San Andreas, only way bigger and with more machine guns.) And, it's having a three-way collision with the Rift Valley, and someday East Africa's going to wind up in the Ocean. (Being from California, I know the feeling.)

But, but... If Northeast Africa's spreading, is Northwest Africa colliding with another plate, and therefore creating mountains, and highish deserts. (Rain gets dumped in the mountains, so the other side of the mountains stays dry and hot? Looks like I need meterology 1A, also.)

To be continued, if anyone's interested. Meanwhile, here's a nice look at the Air Mountains in Niger:

Rock & Roll, was: Why do deserts like volcanos? by Kbee on 13 May 2003 4:56pm
I sent this question to Ali Pezeshkpour at www.usgeology.com, and got this great response. (Oh, so that's what's up with Mount Adams...)
Deserts are usually regions that occur along the 30 and 60 degree parallels, and also occur in areas that lie behind major mountain zones. The main reason as to why deserts occur behind mountain ranges is the rainshadow effect, where moisture gathers on the winward side of the range and precipitation occurs while the opposite side is left void of major rainstorms or other forms of precipitation. This is the case with the Great Basin and Mojave Deserts as they lie behind the Sierra Nevada's and Cascade Range.
Some deserts are high in prehistoric volcanism and may contain many cinder cones and lava flows from short, ephemeral eruptions. There is, however, usually no direct relationship between deserts and volcanism; many deserts, however, do contain many-a cinder cone and other forms of volcanic activity.
It is important to keep in mind that deserts are not always sand and salt flats--the large Tundra regions of northern Canada and Russia are also considered deserts, along with the cold icy regions of southern Argentina and Chile.
In North America and the Great Basin, Mojave, and Colorado/Sonoran Deserts, however, there is some relationship between the desert and its past volcanism. If we look at the San Juan de Fuca plate, we see that it is slowly being sucked underneath the North American plate. As a result, we have the current volcanism of the Cascade Range and the past volcanism found within the Sierra Nevada Mountains. In the past, there was subduction occurring all along the Pacific Rim of North America, from the Coco Plate (Mexico and Central America) up to Alaska. Now, the subduction only occurs along the Mexican and Central American Isthmus, and northern California up to Alaska. In the early stages of the subduction, the subducting plates would slide underneat at a very shallow angle beneath the North American Plate (let's say -20 or -30 degrees). The subduciton would result in volcanism at the end of the plate where the magma would rise into the floating (N. American) plate and result in volcanism. We can see examples of this past volcanic activity with extinct volcanoes such as Mount Adams, which lies to the East of the main Cascade Range in Washington State.
Eventually, the spreading ridge that resulted in the pushing of the San Juan de Fuca Plate and other plates underneath the N. American plate itself subducted beneath the main plate, resulting in a disappearance of the ridge underneat the North American plate. The rifting, however, continued, and resulted in the formation of the Owens Valley and Death Valley, along with the many Basin-Range areas of Nevada and the rest of the Great Basin. There were also many rifts in the deserts, behind the current volcanic ranges such as the Sierra Nevadas, which resulted in the ephemeral formations of cinder cones and lava flows such as those around Amboy Crater, Pisgah Crater, and other cones located in the Mojave Desert of California. This activity continues today, with volcanoes having been formed in recent ( as in the past 2000 years) history. Major rifting and normal faults also occur today in the Owens and Death Valley, (along with more minor ones such as the Panamint Valley), where volcanoes have been formed in recent history such as the Mono Craters (around Bishop, CA) which last erupted around 200 years ago.
Thus we can see that there is no direct relationship between the deserts and volcanoes of the world, but that there is some relationship between the current volcanism of many volcanic mountain ranges and the volcanism of the deserts that lie behind them.
Hope the information helped,
Ali Pezeshkpour
Re: Rock & Roll, was: Why do deserts like volcanos? by sleepydumpling on 14 May 2003 6:57am
Thanks Kbee - that's fascinating! I only wish he went into more detail about the Sahara - but after all, he is a US geologist, rather than a world one!

Interesting information!
Re: Why do deserts like volcanos? by ilse on 14 May 2003 12:13pm
yeah, thanks kbee : )

(see, this site is educational!)

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