Friday, 19 September 2008

Back to the American southwest - if only!

As promised, it's back to geology today and in particular, to the state of Utah in the American southwest. While my family and I were captivated by Arizona during our visit, the next state north from there, Utah is home to some truly stunning scenery and geological marvels as John Crossley's web site highlights.

Dominated by Entrada sandstone, this area has been beautifully sculpted by nature to form over one thousand arches of this layered red sandstone. While many are tiny cavities as small as three feet across, there are others that span huge distances. The largest arch is called 'Landscape Arch' which spans a massive 89 metres.

Landscape Arch in Devils Garden, Arches National Park, Utah
(Photo courtesy John Crossley @

It seems I need to make that trip back to USA fairly soon as this magnificent arch is unlikey to survive much longer. Much of it's length is less than a metre thick and already has several serious fractures. The area surrounding it is now closed and it is awful to think that someday fairly soon it will come crashing to the floor, leaving just a pile of broken rock! Such collapses are not uncommon as on about 3rd August 2008, one of the most famous and most photographed features in the park, 'Wall Arch' collapsed.

Wall Arch before its collapse

(Photograph courtesy John Crossley,

(Wall Arch following its collapse, August 2008

(Photo by API National park Service)

No-one witnessed it's dramatic demise, but that is geology for you! A formation which to you and I may seem beautiful at this moment in time is merely a small step in the geological process of erosion back down to individual particles again, ready to be deposited elsewhere to begin the whole process all over.

So perhaps we need to enjoy spectacular features like these while they are here and not take them entirely for granted!

Double Arch, the Windows section, arches National Park, Utah.
(Photo courtesy John Crossley

Some features are more 'tunnel' than 'arch', such as this formation, aptly named 'Tunnel Arch'!

Tunnel Arch, Arches National Park, Utah

(Photo courtesy John Crossley

The far side of Double 'O' Arch, Arches National Park, Utah

(Photo courtesy John Crossley

Rock formations in the windows section, possibly the surviving remnants of previous arches?
Arches National Park, Utah.
(Photo courtesy John Crossley,

As well as Arches there are other stunning features to marvel at......

A small canyon, near Delicate Arch, Arches National Park, Utah.
(Photo courtesy John Crossley,

Fins near Courthouse Towers in the Windows Section of Arches National Park, Utah

(Photo courtesy John Crossley,

So how did the Arches form?

How on earth did these spectacular arches come to be? The formation of the amazing buttes at Monument Valley I can just about understand, but 1000+ arches in one area? So, a little reading was called for and this is what I found:-

Okay, around 300 million years ago the Colorado Plateau area as Ron Blakey's paleogeographical maps will show you, was ocean. With the passage of time and a great deal of evaporation, a huge salt bed was left behind. These salts were eventually overlain with sand sediments ultimately forming a sandstone layer over the salt bed. However, under pressure salt becomes unstable and the area became subject to distortion and buckling, forming domes and folds. Increasing pressure creates faulting which exposes the formations to the erosional effects of the elements, creating 'fins'. These in turn are eroded away such that in certain circumstances holes are created through them - the start of the formation of an 'arch'.

Okay, that may be a fairly simplistic explanation of their formation, but it at least gives you an idea. Fascinating though, don't you think? Just google 'Arches National Park Geology' if you want more details!

Now, any fellow English persons looking in may well be wondering quite what I have against the geology of good ol' Great Britain! Well, the answer is absolutely nothing and this is something I will start to rectify in future posts!

Stay tuned!

Cheers for now,


1 comment:

  1. Hello,
    Nice set of pics here, thanks for posting. One idea - the rock formations in the windows section, possibly the surviving remnants ...
    appear to be liquifaction mounds, where more liqiufied material squeezed up from under a more solid matrix into overlying material. The liquified sand, water, ?? mix then hardened, and the intervening material then eroded away, leaving these outcrops of hardened (and scientifically mysterious) sandstone.
    Best wishes,


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