nuée ardentes

 

Nuée ardentes (glowing clouds) at Mt. Pelée. 

photographed (and named) by Alfred Lacroix. 

December 16. 1902. 

crustal growth

here is a neat image showing crustal thicknesses across the planet. The two thickest regions are in Tibet and the central Andes. The colours represent surface elevations.

 

This image is sources from the USGS, but I got it from Cawood et al., 2012. This paper discusses the current state of affairs of their understanding of the evolution of the continental crust. A major question is whether crustal growth was accelerated early in Earth's history, or if it has been more or less steady going. Here are some of the options:

 

I like the style of Condie and Aster, 2010. Buenas hondas. 

Below they show the idea that prior to 3 billion years ago, a different set of processes dominated the formation of the continents compared to the typical plate tectonics that we see today. In these early days, the mantle was much hotter and convection likely occurred at fairly shallow levels. Melting of dense, thickened/dripping, basaltic crust is thought to be the dominating mechanism of continental crustal formation at this time. After the earth cooled down a bit, subduction-as-we-know it took over, and continental crust began to form by andesitic volcanism at subduction zones, with the occasional delamination of the mafic roots.

 Cawood, P.A., Hawkesworth, C.J., Dhuime, B., 2012, The continental record and the generation of continental crust, GSA Bulletin.

accretion vs. erosion at subductio zones

Here is a figure from Clift and Vannucchi (2004) showing which subduction zones are adding material to the continental crust (accretion), and which are actively scraping away the continental crust (erosion) and dragging it into the depths.

Accretion is occurring in the Cascadia (forming the coast range), and eroding in the central Andes (exposing magmatic rocks from Jurassic subduction).

Clift and Vannuchi explain that accretion occurs where rivers introduce large volumes of sediments into the subduction trench, such as the Columbia river in Cascadia. In arid regions such as the central Andean coast, sediments are few, and continental erosion dominates. 

Clift, P., Vannucchi, P., 2004, Controls on tectonic accretion versus erosion in subduction zones: Implications for the origin and recycling of the continental crust, Review of Geophysics, 42.  

Tulul Al-Safa - ghuluww

there is this volcano in syria.

in the desert. far from a plate boundary. no good excuse to be there.

the druze have been hiding out there for years.

there were named after a heretic
who exaggerated a bit too much.
but never got around to changing the name.

nobody knows the chemistry of the lavas. as far as i can tell