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Kilbourne Hole – turbidity currents on land!

March 28, 2014

Callan Bentley over at Mountain Beltway just posted about Aden Crater, and I though i would share a few photos from Kilbourne Hole, a nearby maar volcanic crater.  It’s only about 15 miles from my childhood home, and I went there quite a bit in high school, both for geology and just to get out into the desert (mainly to drink beer).

Geologically speaking, it is the crater that resulted from a magmato-phreatic explosion, or when, as Wikipedia says:

rising magma super-heats water-saturated earth, far enough below the surface that a high pressure can be contained. At some point, the pressure is too much, and a steam explosion occurs, throwing the earth out in a catastrophic event. Country rocks are fragmented and expelled in the atmosphere (together with fragments of the magma), eventually creating a deep crater, the bottom of which sits below the pre-eruptive ground surface.

For some nice images of other maars in action, go here.  The main reason I like these features so  much is that the ash cloud that the eruption produces (called a base surge) is a sediment gravity flow (just like a snow avalanche and a turbidity current).  So, these are just really hot turbidity currents on land!

Looking on Google Earth at Kilbourne Hole and nearby Hunt Hole, you see one peculiar thing – there is a prominent ridge on the eastern side of the crater, but not the western side.  This is thought to be due to westerly winds (i.e., winds out of the west blowing eastward) during the eruption that pushed most of the ash to the east.  The wind in west Texas and southeastern New Mexico usually blows out of the west, and since this eruption only occurred ~25,000 years ago, I think that explanation makes good sense.

Kilbourne Hole map view

In the above photo, you can see the ridges on the eastern side of the crater, and I made a simple cross section showing the formation of the ridges and dunes from the explosion.  Type in these coordinates in Google Earth to get you there – take a look at it yourself!    31°58’19.35″N, 106°57’45.23″W.

Kilbourne Hole perspective view

Looking north, you can see the right hand side (eastern) ridge is much higher than the western ridge.  This is due to the wind blowing the exploded ash and bombs eastward.  The crater is large – 2 x 3 km and 12 m deep – looks impressive from the ground:

Kilbourne Hole rim

 

One of the biggest attractions at Kilbourne Hole are the xenoliths full of beautiful green olivine – Callan has some nice photos here.  However, we came to look at the base surge deposits on the rim of the crater, which formed when ash was falling after the explosion and piling up into big dunes and ridges on the eastern side of the crater.  They are impressive, and quite thick:

Kilbourne Hole base surge

 

In the above photo you can see many dune forms, which are all made of accretionary lapilli, which are basically sand-size ash clumps.  If you want to learn more about these kinds of deposits, take a look at this thesis.  A detailed photo of the lapilli is below.

Kilbourne hole accretionary lapilli

Note that these deposits are normally graded (biggest grains on the bottom), as is common in many places where sediment gravity flows deposit sediment.  Almost all turbidites are normally graded – see here and here for more info.  And if you ever drive through the area, do yourself a favor and take a trip out to Kilbourne Hole (only takes 1 hour from downtown El Paso) – you’ll be glad you did.

My first foray into gigapanning: Slaughter Canyon, Guadalupe Mountains, New Mexico

September 17, 2013

Geologists are always taking multi-picture panoramas of outcrops and other geologically interesting phenomena, but then have to go back to the office and use photoediting software to stitch them together into a seamless image.  The problem lies that the stitching is often imperfect due to photo overlap and the resultant images are hard to view on the computer because they are so large.

Gigapan (http://gigapan.com/) found a way to make this process better – you stick your camera into a small tripod mounted robot and tell it to take a large panorama (aka a gigapan), and then use Gigapan software to stitch it together and upload it onto the internet.  The online viewer is pretty slick, and as you zoom in the resolution improves.  In short, it is definitely the way to view large photographs interactively.  You can even tag parts of a photo with a description of what is there.

Zoltan over at Hindered Settling introduced me to this whole Gigapan process (check out his Gigapan page too) , and we have taken many gigapans together.  However, I wanted to try it on my own, so I took the robot out to the Guadalupe Mountains to test it out.  My camera skills arent spectacular, so my first gigapan has a few vignetting issues, but it is still really cool.  Since I was using a telephoto lens, this image is made up of 351 photos, resulting in almost a 3 gigapixel image!

This subject of the photo is a place called Slaughter Canyon, a prograding and aggrading Permian carbonate shelf margin.  You can clearly see the progressively younger reef fronts moving from lower left to upper right.  You can also see the very steep forereef slopes exposed just to the right of the cliffy, massive reef fronts – the one at far right is the best and longest slope, and gives an indication of the relief on this margin ( about 300 m).  Here is a diagram showing the general morphology of that carbonate reef – if you could have walked around here in the Permian, this area may have looked somewhat similar to the modern coast near Oman, with dry desert on land and a carbonate reef in the shallow ocean.

The image below should link to the actual gigapan, but here is a link too.  Be sure to push the full screen button and scroll around to see the full resolution.  Enjoy!

slaughter canyon

Accretionary Wedge #58: Signs!

July 23, 2013

After a long hiatus due to general craziness at work and at home, I am starting up the blog again with this call for a cool geology sign.  The Ross Sandstone is a upper Carboniferous (Pennsylvanian) formation along the coast in western Ireland that is famous for its excellent turbidite channel and lobe exposures.  See this page for more details.  If you haven’t got the chance to go see those rocks and the beautiful countryside of the Emerald Isle, I highly suggest a trip.

In fact I will be there next week teaching a field trip, so maybe I will do a little day-by-day blogging about the rocks there.  Stay tuned!

ross

The Bouma sequence and turbidite deposits

November 7, 2012

For a while now, the most popular page on my site has been this one, a photo of a Halloween pumpkin I carved to look like the Bouma sequence.  It is the most popular because people are looking for information about the Bouma sequence, so it is time to do a real post on the Bouma sequence, with more detail about turbidite deposits and the turbidity currents that produce them.

Turbidity currents are a type of sediment gravity flow where turbulence is the dominant mechanism for grain support.  A turbidity current that is more familiar to most people is a snow avalanche.  A turbidity current is structured like the image below, with a head, body, and tail.  In (A), grains are represented by the black dots – note that the coarser grains are located near the bed and towards the front of the flow.  In (B) is a turbidity current produced in a laboratory experiment that shows the downslope evolution of the flow.

Turbidity currents in the world’s oceans produce spectacular seafloor architectures like canyons, channels, and lobes/fans, depending on the amount of erosion or deposition taking place at a particular location. The sedimentary architecture is influenced by many factors, including grain size and distribution, slope gradient, sediment supply, etc etc etc.

Turbidites are the products of deposition from a turbidity current.   The simplest case is a current that is slowing down (waning) and entirely depositional (e.g. on a lobe).  , a turbidity current produces the classical turbidite, which was famously described by Arnold Bouma in 1962 and interpreted by Roger Walker in 1965.  The Bouma sequence, as it has become known, is the idealized sequence of sedimentary structures that represents the waning of a turbidity current as it passes over a single point.  The five Bouma divisions are (in stratigraphic order):

top

Te – pelagic mud

Td – planar laminated mud produced from suspension settling

Tc – ripple or climbing ripple cross lamination

Tb – high velocity planar lamination

Ta – structureless (aka massive) division

base

An important concept reflected by these structures is that the energy (bed shear stress) is decreasing upwards as the current passes by, and this is also manifested in the normal grading of the bed – coarser at the base, finer at the top.  This photo from the Mt Messenger Formation in New Zealand says a thousand words (this was published in a cool paper in Nature Geoscience):

Note the nice normal grading in the deposit (coarser stuff is slightly tannish in the Ta-Tb, then going to grey in the Tc, and finally to mud in the Td-Te).  The squiggly yellow line in the photo is caused by the denser sand loading into the soft mud at the start of deposition.  Notice that this loading repeats in the bed above, suggesting fairly high sedimentation rates.

The Bouma sequence can also be expressed in a cartoon fashion:

Many variations on the Bouna sequence are possible: it is common to lose the Ta in distal environments where there is not enough energy in the current, and in proximal settings, amalgamated Ta beds are common, where the rest of the sequence was either never deposited or eroded away.

The next post will focus on the processes of deposition of the Ta division and how the Bouma sequence relates to the ‘Lowe’ sequence, which is typically used to describe much coarser grained turbidites…

Geology on the Wing Wednesdays #11 – Mississippi River meander bend at New Madrid, MO

November 7, 2012

The blog has been quiet for a while, but here is one I had to share.  This photo was taken about 35,000 feet above the Mississippi river near New Madrid, MO.  New Madrid is famous for earthquakes in the early 1800s that altered the course of the river (see this ppt for an overview).

The reason I took this photo was not about the earthquakes, but about the large meander bend that is nearly at cutoff.  Flow is from lower left to upper right, and this bend is only 1 river width away from becoming an oxbow lake.  For a nice time lapse view of how this happens, click here.  Given current channel migration rates (~50 m per year for undisturbed portions), this cutoff will occur within the next few years (unless the Amry Corps of Engineers chooses to fight the river and reinforce the banks).  I suspect they have already done so (an intrepid reader could check the Google Earth time slider bar…)

Video of a turbidity current!!

July 21, 2012

This is the coolest thing I have seen in a long time – thanks to Dave Petley for the link.  This event occurred in Cabo San Lucas, on the southern tip of the Baja California peninsula in Mexico.  I imagine that these divers were reef-diving (as evidenced by the angelfish in the first few seconds of the video).  This turbidity current starts out as a small flow on a very steep slope (more than 30 degrees) and is quickly overtaken by the main part of the flow.  The real action starts then, as this current is moving very fast (more on speeds below), and it much thicker and turbulent.  This flow quickly overtakes the scuba divers and keeps flowing downslope.  You can see in the video that the flow keeps thickening with time, entraining the surrounding seawater (here is a paper about how hard it is to model entrainment).

I ballpark this flow to be moving about 5 m/s, or about 10 mph (from my rough estimates of distance in the video), which is similar to turbidity currents measured in nature.  Jingping Xu measured currents with instruments in Monterey canyon at 2.8 m/s, and numerous papers measuring submarine cable breaks estimate speeds from 5 to 25 m/s.  It is important to note that velocity and speed are two different things, and that shear stress is more important than either when discussing sediment movement (i.e. erosion and deposition) associated with turbidity currents.  More on that in another post.  For now, just enjoy the turbidity current – click this image to see the video – I cant figure out how to embed the video…

Here is the link in case you need it – http://www.liveleak.com/view?i=c45_1342620679.  This is awesome.

A photo tribute to Boris Avdeev

May 5, 2012

Boris Avdeev, a brilliant young geologist, and a friend, has passed away.  He went up into the High Sierra on April 19th, and was found by a recovery team on May 3.  He was 31 years old, and a recent PhD graduate of the University of Michigan, specializing in low temperature thermochronology and its application to tectonic evolution (see his recent paper).  He was due to start a post-doc at UC Berkeley soon, and will be sorely missed by all who knew him.

I first met Boris in 2003, when he came to the US to pursue a masters degree at the University of Texas at Arlington (UTA).  I was an undergraduate there, and I recall thinking, “damn, this guy is really smart!”  Although he spoke little english at the time, my buddy Walt and I prided ourselves in teaching him english.  His accent was very heavy then, and I remember a time when he wasplanning a hiking trip, and he was practicing with me how to say “Howdy” and “Good morning” and “Afternoon!” so that people wouldn’t think he had an accent when he passed them on the trail!

Throughout the next few years, Boris and I spent quite a bit of time together in classes, on research projects, and playing in the outdoors.  We spent a memorable summer mapping abandoned river meanders along the Missouri River, which resulted in 4 published quadrangle maps (here is Boris’ map).  We both moved on from UTA in 2005, Boris going to Michigan and me to California.  We kept up, though, and saw each other when we could – the last time was at AGU in 2011, where we reminisced about our days in Arlington.

I will tell one funny story about Boris, and then Ill let the photos do the rest of the talking.  In 2003, we went to a bar with Boris and he wasnt yet acquainted to American bar traditions.  We ordered beers, and in typical Boris fashion, he said, “I would like a glass of vodka.” The waitress came back with a shot glass of vodka and he scoffed, and pointed at a cocktail glass, and repeated his order.  She poured the shot into a glass, thinking he wanted it ‘neat.’  But Boris had other plans and proceeded to tell the waitress that he wanted a full glass of vodka.  She complied, and he slugged it down, and said, “One more!”  It brought the house down, to say the least!

So, here is a photo tribute of sorts, based on a few photos that I have of Boris from his early days in the US (2003-2006).  Unfortunately, I don’t have a lot of photos from that time, due to the fact that I though digital cameras were a fad, but here are a few:

Boris, Walt, Lance, and myself went on a 3 day hiking trip in Big Bend in the winter of 2004, and then Boris came home for Christmas with me – we had a blast that winter hiking, and it is one of my favorite memories of Boris.

Before our big hike – Boris (third from left) looking stoic as ever.

During the hike – Boris again looking unconcerned.  Just after this photo was taken, Boris was making fun of the instructions on an MRE that we packed for food, and got a huge kick out of the fact that the instructions said to prop the heater packet on a “rock or something.”  The photo in this link shows the instructions, and maybe you had to be there to get the joke…

Now he is excited about something!

Boris with friends at Christmas, 2004.

The next group of photos shows one of several canoe trips that we took during our time at UTA, and Boris and I shared a canoe on this particular trip.  He was, as always, full of energy and a blast to be around.

Boris and Tatiana enjoying the canoe trip and passing the bag-o-cheap-wine that we brought…

Boris ‘wielding’ a canoe paddle to get the wine back.

This last photo is from 2012 from his Google+ page.  Boris was a great scientist, a mentor to Walt and I, and a great friend.  His enthusiasm and energy was unparalleled, and this photo typifies him – doing what he loved in the outdoors with his friends.

{UPDATE, May 8, 2012} – please also visit this website www.borisavdeev.ru, or the english version www.borisavdeev.com to see more photos, or to submit your own.

 

{UPDATE, January 11, 2013} – Jim Lewis from Richardson, TX has sent me his tribute to Boris – download the word document here.  Also, Jim alerted me to this link about Boris’ experience with the law while at UT Arlington – I had forgot about that, but it made me smile – that was Boris!