A graphic designer under the pseudonym “A Common Name” has made some beautiful geode street art. Cruise over to their page to check out all the pics. Below are some highlights.
Check out this really cool real-time wind map of the United States. You won’t be able to look away.
Scotland is thought by some as the “birthplace of geology” as it is where James Hutton developed the theory of uniformitarianism. Well, it looks like the Scottish Qualifications Authority is looking to cut geology from the high school curriculum. A high school teacher is launching a campaign to stop this from happening. I heard about this through this Reddit thread: http://www.reddit.com/r/geology/comments/rhokw/help_us_rgeology/
The starter of the thread is inviting people to contribute reasons/arguments as to why cutting high school geology is bad. Feel free to post your thoughts on the reddit thread or here.
I posted a link to this talk back when it was streaming live and now it’s finally up for viewing. Dr. Jamie Kirkpatrick, a post doc at UC Santa Cruz, gave a talk at the USGS on pseudotachylites and how we can glean information about past earthquakes from the rock record. Watch the talk here.
Sometimes during lunch or breakfast I like to put on a TED talk. Here Regina Dugan gives an inspiring talk about how removing the fear of failure unleashes the impossible.
Last week the Tectonics class I’m TAing had an extra “throwaway” lecture. We decided to let the students build their own experiments to gain some intuition about Low Reynolds number flows, and what the Reynolds number means.
The Reynolds number is a dimensionless number that can be characterized as:
Re = (Density * Length * Velocity) / Viscosity
Re = Inertia / Viscosity.
Generally if the Reynolds number is below 2000 the flow is laminar, greater than 2000 the flow is turbulent.
To tie it to geology we helped the students work through an order of magnitude calculation of mantle viscosity. Try it for yourself: Density = 3300 kg/m^3, Length = 3 X 10^6 m, Velocity = 1 cm/yr, Viscosity = 10^21 Pas. What do you get? Is the mantle a turbulent or laminar flow?
After the video we gave the students a set of ingredients and beakers to play with: canola oil, molasses, water, food coloring, and glycerin. Fun fact about glycerin, the pharmacy only sells small bottles and employees will give you VERY strange looks when you ask for a liter of the stuff.
Here are the experiments the students came up with. You’ll here conversation about flows, mantle winds, and non-school stuff in the background.
First up we have molasses poured into glycerin:
and a small amount of molasses…
My favorite: a two layer system. Bottom layer is glycerin and top layer is oil.
And a turbulent flow for good measure…
Some things to take away from the student’s experiments: our containers were too small in height for the low Reynolds number plumes to fully develop before hitting the bottom. This would also require much more glycerin, and more weird looks.
And for fun here’s a video I found of a low Reynolds number (~1000) vortex ring collision. Science is so sexy.
So I finally finished my #SciWrite manuscript. I just submitted a manuscript to G-Cubed: Geochemistry, Geophysics, Geosystems. The manuscript was based on my undergraduate thesis at UC Santa Cruz on the Yellow Bank Creek Complex, the world’s largest known exposed sand injectite complex. It’s an amazing outcrop. I’ll be writing a field trip guide for the outcrop in the near future, a version of which will be posted here. I’m very excited to finally get it off my desk. Now I can get back to blogging! And onto planning summer field work, grading those labs…
|Northern side of Yellow Bank Creek Complex outcrop. Yellow-tan sandstone is limonite cemented. Blue-grey sand is dolomite cemented.|
Also, now that I have a submitted manuscript I updated my CV with it and finally set my McGill webpage live. I have a lot of awesome pictures posted there. Check it out. Please if you have any comments about that site (or this site too!) I’d love to hear feedback. Am I missing something crucial to my webpage that every grad student should have?, ect. Let me know!
I also want to work on a re-design for this blag, that’s on my farthest backburner, though. Any ideas?
One useful student-thing I got in the habit of doing my senior year at UC Santa Cruz was scanning my class notes. There was a color scanner on the office copy machine that would email me pdfs of my notes. Perfect. I could access my notes from anywhere (via DropBox) and if my notebook exploded, I had back ups.
|Artists rendition of a Bergship|
War brings out the best in people. Okay, so that needs some explanation. What I mean here is that solutions that would normally be labeled ridiculuous or insane are considered plausible and explored with fervor.
Note: The following information is taken from Perutz 1948.
Therefore the cheap construction of gigantic aircraft carriers was considered. Mr. Geoffrey Pyke submitted a plan in October of 1942 where he proposed that an iceberg should be hollowed out to shelter aircraft and leveled to provide a runway. This craft would travel at a few knots.
|Pykrete ship design|
Why make a boat out of ice? Well for one it would unsinkable. Ice is difficult to break with explosives (shown by resistance of icebergs to shellfire) and melted very slowly when insulated. Thus, the Allies began researching the possibility of constructing a “bergship”. An ice thickness of 15m was considered essential to operating aircraft from the deck of a carrier and the minimum runway size for bombers was 600m with 60m the most desirable width.
To design such a ship the mechanical strengths of ice needed to be known. However it was found that some icebeams would fail at stress as low as 4.9 kg/cm^2. To compare, pine wood has a rupture modulus of 800 kg/cm^2.
It was discovered that the inclusion of wood pulp in the ice increased its strength considerably. This substance is known as pykrete.
A fantastic amount of research was done on pykrete to learn about its behavior under stress. A cylinder of pykrete was loaded with a stress and the resulting deformation measured. Differing percentages of wood pulp was tested with 14% wood pulp to ice performing best for the materials. Pyrkete’s resistance to projectiles was also tested as seen in Table III from Perutz 1948:
|Table III from Perutz 1946.|
There’s plenty of videos online demonstrating the strength of pykrete versus ice:
Based on the results of underwater explosives tests the effect of a torpedo hit would produce a crater 60 cm deep and 4.5 m in diameter. Regardless, a wall thickness of 9.0 m was suggested to keep the bergship safe from torpedo attacks.
The result of the stress tests on the pykrete showed that the strength of pykrete was dependent on the rate of loading. The load at which pykrete failed would be greater the slower the rate of compression. An added difficulty became apparent. With a very slow compression rate the pykrete would not fracture at all. Instead the cylinder would undergo plastic deformation until it was the shape of a flat disk.
Thus the possibility was considered that a ship of this size would deform under its own weight. The creep properties of pykrete had to be tested. Samples of pykrete were loaded with differing stresses:
|Figure 2 from Perutz 1948.|
What we see in the above figure is total compression in inches is plotted against time for contours of differing initial loads (kg/cm^2). What we see that loads have a rapid initial compression and then slow until a constant rate of compression is achieved.
Based on the creep curves, it was decided that a bergship would undergo plastic deformation for a period of several weeks until deformation ceased.
Thus the design of a pykrete ship was undertaken. The hull would be surrounded by a waterproof, artificial skin and the walls would be maintained at a constant temperature of -15 degrees C through artificial refrigeration. Each ship would have 16 refrigerating plants necessary to cool the ship. The berg ship would be propelled by 20+ electric motors. However difficulties in design and also the shear scale of resources necessary (1,700,000 tons of pykrete per ship) to construct a bergship led to the project being abandoned.
Although the project to construct a carrier out of pykrete failed, much insight was gain into the behavior of ice and glaciers. The tests on pykrete showed that the creep mechanism was “quasi-viscous” flow and suggests the same for glaciers. Quasi-viscous flow is achieved through rearranging atoms in the crystal lattice either within individual crystals or across grain boundaries. This creep mechanism differs from melting and refreezing creep which was originally thought to be the creep mechanism for glaciers.
One cool feature of Perutz 1946 is that after the paper finishes, there is a discussion attached to the end. It is concluded that pykrete could be used as an effective runway material in arctic countries.
Perutz, M. F., A description of the iceberg aircraft carrier and the bearing of the mechanical properties of frozen wood pulp upon some problems of glacier flow. Journal of Glaciology, Vol. 1, Issue 3, pp.95-104, 03/1948