Back in Bangladesh

We're back in Bangladesh now. We're spending the week exploring more anticlines (folds) and meeting with our colleagues who study the rivers. Today we got to see tube well drilling.

There's a special drilling technique they use in Bangladesh. One member of the drill team uses their hand as a valve, just like you might use your finger to keep suction to lift water up in a drinking straw. Three or four other guys pull on a lever to lift the drill pipe up. They can drill really deep!

Each time the pipe drops down, a squirt of sand, mud and water comes out the top. They catch some in a bucket and then they can study its composition and see how it changes as they dig deeper. 

Our colleague Professor Goodbred has an awesome tool called the XRF. It stands for X-ray Fluorescence. It shoots x-rays at a sample of sand and measures different elements. The chemistry can tell us where the sand came from! This helps us learn about where the rivers were in the past. We work with scientists who study rivers because rising mountains and earthquakes can cause the rivers to change course!

 We've been having a little bit of trouble in Bangladesh because they've had some political strikes called hartals. During a hartal, cars can't drive around because people set up road blocks and may attack cars. During the 48 hour hartal, we needed to work so we had to take a truck on the dirt road through a national park. It was a bumpy ride. We didn't see any angry mobs. It was very peaceful and we even saw a monkey with a baby!

Faults and earthquakes!

At a rock outcrop, the main things we look for are bedding planes (that were originally flat) and faults. Faults are cracks in the rock where the rocks have moved. Huge faults can produce huge earthquakes. Little faults can help us learn about tectonic forces and buried faults that we can't access.

We were really excited to find some big faults on this trip in India. These faults cut through basalt, which is a really hard igneous rock. Igneous rock forms from magma or lava instead of sand and mud.

This fault had a layer of crushed up rock almost three feet thick. We were able to climb inside the fault zone to take our measurements!

There are three main kinds of faults: normal, reverse and strike-slip. Normal faults happen when plate tectonic forces pull apart and reverse faults happen when the forces push together. Strike-slip faults are where plates move past each other, like the San Andreas fault in California. The main fault I'm studying is a kind of reverse fault and the tectonic forces push one plate over the other.

Sometimes it can be hard to figure out which kind of fault you're looking at, so I have to make careful observations (even if that means climbing into the fault zone!)

On January 9th there was an earthquake nearby, but we didn't feel it. It was an interesting earthquake because it was really deep and east of the Dauki fault that I'm studying. Maybe the Dauki fault continues farther than everyone thought!
Here's a link to a summary of the earthquake (it has a map so you can see the earthquake location):
http://earthquake.usgs.gov/earthquakes/eventpage/usc000elmf#summary

Detective work

Geologists are like detectives. We are trying to piece together the story of how and when the rocks formed and how and when they have moved. Every rock has a story to tell about the environment when it formed. The rocks in these mountains also tell the history of motion on faults underground.

In answer to Dayleni Grullon’s question, one of the rocks we study in this part of India is limestone. You may remember that I passed a piece of it around the classroom back in September. The limestone is made from the shells of creatures that lived in shallow ocean water. We can figure out when the limestone formed because it has fossils of animals that went extinct. So the rock told us that there used to be an ocean here X million years ago, before the mountains formed!

Next I try to figure out what story rocks can tell us about plate tectonics. I use my special compass to measure how the sedimentary rocks have tilted and I make a map. My map tells us which way the rocks have folded and that tells us which way they’re being pushed by plate tectonics.

Limestone is also really cool because it can be dissolved and form caves. We found and explored a cave in India! We found stalagtites that have been tilted, and my friend Chris is going to measure how old they are so we can estimate how fast they are being tilted. He’s also going to measure the age of broken stalagtites to try to figure out when ancient earthquakes happened so we can estimate the repeat time of earthquakes here. The cave was a little bit scary – I saw a HUGE spider! (that's Professor Seeber's hand. He's braver -- or perhaps more foolish? -- than I)

Luis Tapia asked how rocks are folded, which is a really great question. Sedimentary rocks are formed in horizontal (flat) layers. When plate tectonic forces push on rocks, they bend and break. When rocks bend the layers become curved and that’s what we call a fold. When the rocks break a fault is formed and that’s where earthquakes happen.

Here's a dramatic photo of folded rock I borrowed from someone else's geology blog so that you can see a really clear example. (http://www.itsasickness.com/geology/content/folded-rock)

I really enjoyed reading all your questions and comments, thanks for all the great ideas for new blog posts! Here's a brief food update:

I was served rice in a banana leaf last week, and yesterday we got to have pineapple for dessert!