The Accretionary Wedge # 41: Something's Slumping

It is time for me to participate in the Accretionary Wedge once again. This month's topic is: What is the most memorable/significant geologic event that you have experienced?

What we seek for AccretionaryWedge #41 is an account of a geologic event that you experienced firsthand. It could be an earthquake, a landslide, a flood, a volcanic eruption, etc. (but don’t feel compelled to stick to the biggies – weathering, anyone?) – some geologic process that you were able to directly observe and experience. - Ron Schott

This is a toughy. I have never seen a volcano erupt, been in an avalanche or really in any life threatening geologic events in my short career. Thus far in my life I have experienced one earthquake, in Ottawa, and a few other smaller events such as watching rivers erode banks, observing coral reefs and sedimentation processes in Bermuda, climbing a glacier in New Zealand. All of these things are cool, but I think the coolest of them all is the time I spent working in the massive retrogressive thaw slumps located in the Northwest Territories where I have done fieldwork. I think it is fair to say that these slumps are geologic events in progress. Indeed, standing in a  slump is to watch ice, rocks, trees and mud cascading from the headwall around you and if you close your eyes you can hear the cacophany of the slumping process all around you, mostly in the form of plopping and thuds.

The Charras slump. It is about 1-1.5km across.

These slumps are formed in permafrost regions and are due to melting of permafrost and a thickening of the active layer, which is the layer of soil that melts on an annual basis. This melting can result either in active layer detachments, which is when the melted surface layer slides off the permafrost below, exposing it to melting, or when the melting occurs on slopes that result in a landslide. These slumps can be extremely large and have a huge impact on the land and watersheds they form in as they dump millions of tons of sediment into nearby streams and lakes.


Basically a slump consists of the three main parts: the headwall, the body and the mudflow. The headwall is the front of the slump where is it retrograding backward into permafrost which then collapses into the hole as it melts. The body is the big hole in the landscape and the mudflow is the trail of sediment that has flowed downhill and either been carried away or is damming a stream. 

The mudflow. This one is about 2-3km long and has completely filled the stream valley.

My work in the slumps near Fort McPherson, NWT consists mainly of taking water samples in nearby creeks, samples of peat moss and samples of ice from the headwall for geochemical analysis of stable and radioisotopes. Our usual routine consists of camping in Fort McPherson and then driving out to near the slumps and then bushwhacking/hiking out over the land to reach them, which takes about 45 minutes. These slumps are an awe inspiring site and every time I go out to them I am truly overwhelmed at their size and the magnitude of destruction they have caused to the land around them. Honestly, walking into a slump is like waking onto another planet because one minute you are surrounded by green shrubs and peat moss and the next mud! Mud is everywhere, completely dominating the landscape and flowing everywhere. In fact, the inside of a thaw slump is like visiting the moon. 

Closeup of the mud with "craters" left by raindrops

The headwall. It is around 30m high. You have to be really careful when on top of the headwall since you can't tell from above if you are standing on an overhang or on solid ground!! Also, when in the slump you have to watch your footing since the mud can be pretty treacherous and suck you in. It is best to travel in groups.

Furthermore, in the summer the thaw slumps are ever changing. I alluded to the sound a slump makes as rock and ice cascade down into the slop below, but it is difficult to describe how rapidly the appearance and conditions can change. For example, a week of sunny weather will lead to lots of melting in the headwall and the collapse of a large amount of land and a rainstorm the following week will wash it all out onto the mudflow. Indeed, features that seem immense one week will be gone the next and don't even think about trying to spot the same features from year to year!! 

Week 1

Week 2. I kind of think this looks like a face. Particularly Sideshow Bob from the Simpsons. Also, notice that the bush on top in Photo 1 is now gone as are many of the trees.

Well, that is my most interesting experience of geology in action: hanging out in a thaw slump. I hope you enjoyed the read! If you have any questions feel free to ask them. Thanks for reading.


Matt

Look out for bears!!

Sampling the headwall.

The 12 Million Years of Christmas

Well it is the Christmas season so it is time to celebrate! Here is a slightly modified version of the 12 Days of Christmas that is more in keeping with the theme of this blog. I hope you enjoy it!

Santa!!

If you would like to find the tune to sing along here is a link: 

http://www.youtube.com/watch?v=NfeSSqWTSQs

On the first day of Christmas,
my true love sent to me
A T. Rex in a tar pond.

On the second day of Christmas,
my true love sent to me
Two oil wells,
And a T. Rex in a tar pond.

On the third day of Christmas,
my true love sent to me
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the fourth day of Christmas,
my true love sent to me
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the fifth day of Christmas,
my true love sent to me
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the sixth day of Christmas,
my true love sent to me
Six geo's a drinking,
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the seventh day of Christmas,
my true love sent to me
Seven miners a mining,
Six geo's a drinking,
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the eighth day of Christmas,
my true love sent to me
Eight slumps a slumping,
Seven miners a mining,
Six geo's a drinking,
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the ninth day of Christmas,
my true love sent to me
Nine earthquakes trembling,
Eight slumps a slumping,
Seven miners a mining,
Six geo's a drinking,
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the tenth day of Christmas,
my true love sent to me
Ten plates a shifting,
Nine earthquakes trembling,
Eight slumps a slumping,
Seven miners a mining,
Six geo's a drinking,
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the eleventh day of Christmas,
my true love sent to me
Eleven volcanoes erupting,
Ten plates a shifting,
Nine earthquakes trembling,
Eight slumps a slumping,
Seven miners a mining,
Six geo's a drinking,
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond.

On the twelfth day of Christmas,
my true love sent to me
Twelve crystals forming,
Eleven volcanoes erupting,
Ten plates a shifting,
Nine earthquakes trembling,
Eight slumps a slumping,
Seven miners a mining,
Six geo's a drinking,
Five flannel shirts,
Four climbing ripples,
Three trilobites,
Two oil wells,
And a T. Rex in a tar pond! 

Hope you liked it.

Matt

GeoMedia: Indisputable evidence of water on Mars!!

The Mars rover Opportunity has found indisputable evidence that water existed on Mars in the form of a vein of the mineral gypsum in bedrock! The vein is about twice the width of a human thumb and half a metre long. This is first direct proof that water existed on Mars and had flowed through a fracture in the rock depositing the gypsum.

This false-color view of a mineral vein called "Homestake" comes from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity. Image Credit: NASA/JPL-Caltech/Cornell/ASU

Gypsum (CaSO4·2(H2O)) is a mineral that is commonly found on Earth often in exactly the same situation as it has been found on Mars. The formation of this vein was likely due to groundwater saturated in calcium and sulphate flowing through a fracture in the bedrock. The highly saturated groundwater then precipitated the gypsum, filling in the fracture and leaving behind a vein of gypsum. Precipitation from water is the only possible way that such a structure could have formed and is the way veins of minerals form on Earth. While this sort of feature is relatively common on Earth, this is the first time it has been seen on Mars. The source of the calcium in the water is believed to be from volcanic rocks that were leached by groundwater. The suphur is likely also from volcanic rocks or volcanic gases that were dissolved in the water as well.

This is not the first time gypsum has been found on Mars as previously gypsum sand dunes had been discovered. However, this is the first time that it has been found in-situ, or where it formed, as opposed to having been eroded and then transported by wind as was the case with the dunes. This means that liquid water actually flowed through this fracture!

For more details here is the link to the NASA article: 

http://www.jpl.nasa.gov/news/news.cfm?release=2011-377&cid=release_2011-377#2

Matt

What is this??

The point of this post is to get you to give me your input on what you think the picture below is. First though, a little backstory...

A few years ago I was on vacation in Australia with a friend. We were travelling around the country and trying to see as much of it as we could. We both felt that a visit to Australia was not complete without a visit to the outback. Luckily, my friend had made some contacts on a previous trip for a school exchange. Therefore, while we were in South Australia we took the bus north to meet up with a friend whose family lived in the outback on a large sheep station about an hour north of Port Augusta, South Australia.

The station was a beautiful place. Wide open spaces with a huge mix of landscapes such as desert, salt flats and the foothills of the Flinders Ranges literally in the backyard. On top of this it was once of the most varied geological environments I have ever visited. All in one small area were limestone beds containing beautiful stromatolites and ripples interbedded with microbial mats.

Stromatolites

Ripples and microbial mats

In addition to these awesome features the station was also home to giant kangaroo bones from the Pleistocene. 

The foot of a Pleistocene kangaroo

The ?femur? of a modern kangaroo being held next to that of a Pleistocene kangaroo.

Aside from the great geological attractions of the station were archaeological curiosities as well such as this aboriginal arrowhead that I found laying in the ground.

Aboriginal arrowhead

However, I digress. The real purpose of this post is to gather your opinion on what you think the upcoming picture is of. I have my own theory, which I will outline below the picture. I apologize for the poor quality. The shape in question was on the bottom of a cliff face which I had to climb up to and then lean out to take a photo of with full zoom. You are viewing this in plan view so imagine a flat surface above your head that contains the shape and you are looking up to see it.

?????????????????????????????????????????????

The rock containing the strange oval shape (~10cm) above is a sandstone and is the bottom of a bedding plane with apparent ripple marks. The red colour is due to iron oxide in the rock staining it red. Any ideas?

My theory, and I like to think that this could be the right one, is that this is a fossil of an extremely ancient organism called Spriggina. Spriggina lived in the Ediacaran, the most recently named of all geologic periods, which spans a time from 635 - 542 million years ago and was the period right before the Cambrian. 

Spriggina. Scale is in mm. (Wikipedia) 

In fact, the name Ediacaran comes from the tiny village of Ediacara, located only a few hundred kilometers north of where I was, in the heart of the Flinders Ranges. Most of the fossils found in the Ediacara area can be seen on the bottom of sandstone bedding planes that contain ripple marks, which is one reason why I think that my picture could be some sort of Ediacaran biota. At least the depositional environment is right as well as the general shape.

The problem with my Spriginna theory is that the fossil in my picture is very large compared to Spriginna fossils that have been found to date which are around 3cm. Who knows though? There are other types of Ediacaran fossils that could also fit the description of this one and maybe it is one of these? Perhaps it is just a strange weathering feature and not even a fossil?

So that is it? What do you think the mystery structure is?

For more information on the Ediacaran see this link: http://en.wikipedia.org/wiki/Ediacara_biota

Matt