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Earth Science Week, Continued: Geologic Maps--The World Beneath Your Feet

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In this fourth installment of our Earth Science Week series, scientist Randy Orndorff gives us the lowdown on how geologic maps show what's down low, and he explains how these maps and the USGS's new geologic time scale and colors benefit planning, development, industry, and you.




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Pat Jellison:

Welcome and thanks for listening to the USGS CoreCast, I'm Pat Jellison. It's October 18th and this is the fourth installment of this week's daily CoreCasts dedicated to Earth Science Week 2007. Today we're joined by Randy Orndorff, Associate Program Coordinator for the USGS National Cooperative Geologic Mapping Program. Randy will help shed some light on geologic maps and their importance to society and tell us about the USGS's new geologic timescale and color scheme for use in creating and using these maps. Randy thanks for joining us.

Randy Orndorff:

Oh, it's great to be here Pat. I'm always excited to talk about geology.


[laughs] So Randy, what are geologic maps. Tell us a bit about them. What do they mean for planning and development, commerce and agriculture, and the average citizens daily life? How are they used?


A geologic map really shows the variety of materials that occur at the Earth's surface. So you can see this would be really important for folks that are looking for various resources...things that are in our daily lives. You think about the wallboard in your house, the cinderblocks, the bricks, the toothpaste you use. There are so many things in our daily lives that relate back to geology and the geologic map points us to where those resources would be. Also for finding water. So for the water we drink the water is contained in the rocks and in the sediments in the geologic maps. So they're important for that also. And for agriculture also for the soils and things like that are derived from rocks.

So the geologic map is there, it's very robust. A lot of people use them and don't even realize it. Although they're not the upfront piece that you would see the public they really are used and one of the biggest sellers of map products in the USGS and in state geological surveys.


Wow. So what can the geologic characteristics of an area reveal other than the things that you've just outlined-toothpaste, my gosh. For example, can studying the geologic makeup of an area tell us if it has potential for oh, say, radon or other hazards?


Oh definitely.That's another piece of the geologic map that's very important. Various geologic units can have contaminants or have natural occurring chemicals that can be harmful. Radon as you mentioned is one of those and that only occurs in certain rock types. Asbestos is another one that is in the ground or in the rock is not necessarily a problem but when construction occurs in it can let loose the asbestos and can be a problem for folks living in those areas.

And other hazards too. By knowing the geology, looking at the structures in the rocks, faults and things like that obviously we can understand better about earthquakes. Looking at the various sediments around steep mountain sides, understand landslides and where those would occur. So yes there is a lot of information that you can gleam from the geologic map.


What about areas of human development?.For example, everybody has heard that parts of San Francisco were built over the rubble and landfill and other debris from the great 1906 earthquake. And many cities have places where rubble was brought in to fill swamps or low-lying areas. Is that considered geologic material and do the maps reflect that sort of thing?


Since there is actual material there, and it is human in nature, we still map it as what we call...a lot of maps will call that artificial fill. And it's very important because you mentioned San Francisco, and that's a place where we really need to know where those materials are because the shaking that occurs during an earthquake on loose sediments and most of those artificial fills is generated a lot higher. So the magnitude or the shaking that occurs in these sediments are very important.

We actually have a project in the San Francisco Bay area where they look at the rocks and the sediments, including the artificial fill and where they are, so we know that the earthquake shaking will be more intense in those areas.


Mmm...very important for local planners. So tell us a little bit about the USGS's new timescale and colors that help in creating geologic maps of the US and North America.


Well Pat, its really all about communication. You know, we have our languages that people need to talk with and when we talk about time, obviously, geology goes back to the beginning of Earth. So more than 4.5 billion years. So we need to be able to understand what the ages of the various rocks and the various sediments are. It's a very important way to communicate. So there are ways that we date rocks. We can date them by radioactive materials within the rocks, we can look at fossils to understand how those rocks may, or when, they've actually formed.

But also we give names to the periods of time so we, as geologists, can communicate with each other. And a lot of people public know some of these. For instance, I think a lot of people heard of the Triasic and the Jurassic [Pat: laughs]-Jurassic Park for instance, the age of the dinosaurs. These are geologic age terms. Over time there's been some controversy and were also constantly revising the actual dates of these periods and the boundaries of these periods. And that's what this timescale is about is to understand for people to have a consistent timescale to use when they're doing their geology, their geologic studies.

This also links into the colors of the geologic map. A geologic map is beautiful piece if you've seen one on a wall before there's lots of colors to them and those colors actually mean something. We give colors to rock units based on their ages. So that's how the colors link to this timescale.


So it sound like a geologic map is a piece of science and a work of art and a history book all rolled into one.


Most definitely.


So, just out of curiosity what are the geologically oldest and youngest parts of the United States?


The oldest part is pretty easy. The Adirondacks of New York and the very northern section of Minnesota around the Lake Superior region where we have a lot of iron formations. Those rocks are well over 1.5, 1.7 close to 2 billion years old, very old rocks. Youngest rocks? Things that are happening on a daily basis- rivers depositing sediments that's geology, but that's happening today. But if you think of an actual rock, probably want to think of lava that's cooling. So, I guess Hawaii to answer your question. My rock collection, I think I've got my oldest get and I have my 1983 piece of basalt and lava from Kilauea volcano. So that's probably what you would say is one of the youngest areas.


Wow, so the message is geology is still going on [Randy: Exactly.] Well, Randy I want to thank you for your time today. We really appreciate you talking with us. Its clear that there's an awful lot we can learn from geologic maps, not just about the ground beneath us but about the environment as a whole and about our daily lives.

Thanks again for joining us.


You're very welcome. I so much enjoyed it.


And thanks to all of you for listening to this episode of CoreCast. Don't forget keep an ear out for tomorrow's podcast in our continuing Earth Science Week series. Tomorrow we'll be talking with Bob Ridky, USGS Education Coordinator resources for students, teachers and anyone else who wants to learn more about USGS science.

CoreCast is a product of the US Geological Survey, Department of the Interior. Until next time I'm Pat Jellison saying, "Keep thinking and stay curious."

[music fades in and fades out]

Musical credit: "Elec_guit_cleanfunk_riff6", Soundgram Post.

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