When Was North Carolina Last Under Water?

We often get queries that ask about local geology that we do not have easy access to. However, it’s fairly easy to sleuth things in the broad brush by locating state geologic maps. I can’t say much about a rock found in someone’s backyard, because glaciers and rivers could have moved that rock hundreds of kilometers from its original source. The following is a local-geology question that I CAN reasonably respond to. 

Q: Can you tell me when was the last time North Carolina was under water? I'm finding fossil seashells yet I live nowhere near any ocean. I live in Jacksonville, NC (Onslow County)

- Brandon F

A: You live on the Outer Coastal Plain of North Carolina; Onslow County runs all the way to the ocean. The Outer Coastal Plain, or Tidewater is extremely flat, averaging less than 20 feet above sea level. It contains large swamps and lakes indicative of poor drainage conditions, which have hosted both freshwater and marine mollusks at different times. The coastal margin north of Cape Lookout is a “drowned coast,” in which sea level rise associated with the end of the last Ice Age, and continual melting of the ice caps, has caused the ocean to invade the lower reaches of river valleys including where you live. This drowning has produced large embayments such as Albemarle and Pamlico Sounds. New River (where you live) lies between this region and the Cape Fear uplift.

You might wish to look at the North Carolina geologic map for more detail:

(https://ncdenr.s3.amazonaws.com/s3fs-public/Energy%20Mineral%20and%20Land%20Resources/Geological%20Survey/1985_state_geologic_map_500000_scale_600dpi_rs.pdf)

To your east you have the Belgrade Formation, with oyster shells embedded in sand. To your north and west you have the River Bend Formation, also fossiliferous with limestone among other rocks. Both formations are listed as Tertiary in age (66 million to 2.6 million years ago). However, the shells you are seeing could conceivably be from the last several tens of millennia if I read your elevations and location correctly.

I hope this helps. You have some excellent geologists in your state, both at the state and university levels. It should be fairly easy to contact one - perhaps visit the closest university and ask to talk with a geologist there. 

~~~~~

Hunting Asbestos

This question opens the door to several issues: indirect detection when direct detection is not possible, and unanticipated down-sides (such as death) to some mineral exploration projects.

Q: Hello Sir,

Could you please tell which is the best method for locating asbestos, pyrrhotite and manganese? Whether airborne magnetic survey or ground magnetic survey?

Regards, Ahtisham ul-H.

A: Asbestos (an aggregate of six different but related silicate minerals) and manganese are not magnetic. Pyrrhotite (FeS) is sometimes weakly ferromagnetic if there are iron deficits in the ideal FeS lattice. However, these minerals are all usually associated with serpentinization, a hydration and metamorphic transformation of ultramafic (dark, iron and magnesium-rich) rock. Serpentinization usually has significant magnetite associated with it, and THIS is strongly magnetic. I've worked in ultramafic rocks where I have personally encountered 3-cm-thick veins of pure magnetite. It doesn’t take much more than a percent or two of this to make a rock really magnetic.

The usual method for mapping these sorts of deposits is ground magnetics and geochemistry, but keep in mind that you are only indirectly imaging the minerals you are interested in. Airborne magnetics are often used for regional surveying, to outline target areas for later follow-up with ground magnetics.

As an aside, please keep in mind that mining asbestos, or fabrication of asbestos products, is dangerous. My father died of mesothelioma-related lung cancer. In his 80's he was an avid bicyclist in San Francisco. The pipes in the basement ceiling of his apartment building, where he stored his bike, were insulated with blown-in asbestos. When he developed a persistent cough, a biopsy showed his lungs to be poisoned with asbestosis.

Immediacy or Temporal Myopia

Immediacy or Temporal Myopia

Much of how we view our world is filtered – by time, by previous experiences, by others’ reactions. This is one reason why scientists keep careful records of their observations and experiments. Otherwise, we would be subjected to the most strongly held, no-basis-in-scientific-fact opinions of those around us. Sort of like the Internet.

Q: There seems to be alot of Earthquake and Volcano activity going on lately within the pacific ring of fire. Is there more earthquakes and active volcanos this year then there has been in a while? Seems rather worrying :(     Thank you!

- Jessica M

A: Not to worry - it has always been this way - there is nothing particularly unusual going on. Please understand that earthquakes and volcanic eruptions do NOT occur in a steady rhythm*. If you average over a 10-year cycle it evens out and looks similar from cycle to cycle. From a much larger window of time - something research seismologists can see because they have decades-long databases to work with - you can see the synoptic view. The larger picture shows these apparent surges in events are just the Earth system puttering along as usual. 

* There is a tendency among human beings that for lack of a better expression I call temporal myopia. We tend to remember only the most recent attention-grabbing events, and focus on them. We also tend NOT to remember as well older similar events, nor the periods of quiescence between them. Immediacy might be another word for this tendency.

Please sir answer this question in 24 hours or... ASK YOUR OWN SOUL!

This is a question that I actually answered in some detail three months ago, so when it came in I thought I would just point the individual at my earlier response. However, I was struck by HOW I was asked this time. To give readers a sense of what we sometimes encounter in our email in-boxes, I share this, but I'm disguising the name and identity of the questioner. You can't make this stuff up, to paraphrase Dave Barry.

Q: Hello sir

In the defination of earthquake

Eathquake is the sudden terror or shaking of earths crust which lasts for the short time. But  in 2015 the earthquake in nepal not lasted for a short time . So why we use that sentance , " which last for the short time".But Generaly in most cases it not lasted for shot time. Sir please answer this question in 24 hrs please sir i sent this question you not answered please answer . Please tel me if you want to hep ,me  or not. I f you want to help, if you want to make a bright student please help me . aSK YOUR OWN SOUL AND HELP.

tHANKYOU

A: 

I cannot answer questions about your soul, nor about mine. This is not something you would ever address to a scientist.

Volunteer geoscientists in the US Geological Survey do not see questions that arrive during western hemisphere weekends. Please do not blame us for not instantly replying to your questions from <Asia>.

I have no idea what definition you are referencing, since you did not provide that information. The simple answer is the larger the moment magnitude (Mm) of an earthquake, the longer the coda. In other words, the greater the energy released, the longer the apparent shaking will last. In fact, you can get a rough idea of how big a regional earthquake is by timing the shaking.

Terraforming Mars

Here's a Q&A that has nothing to do with earthly geology, but may have some instructive content for future geologists. There is usually at least SOME science in SciFi novels!

Q: What would happen to the Martian atmosphere, over the course of the next 100 years, if we could build a machine on Mars that could output the equivalent quantity and composition of greenhouse gasses as are released on earth (approximately) every year?  Thanks for your time, hopefully this has not already been answered!  

- Kyle R

A: That's a rather unique question, but it begs several critical assumptions.

According to a recent Science article, Mars lost its original atmosphere billions of years ago because the planet lost (if it ever had) its magnetic field. As a result the solar wind (high energy charged particles blasted out from the Sun) stripped most of Mars' atmosphere away. So one assumption is that the planetary magnetic field is somehow restored.

Another assumption is a bit more obvious: where would the carbon and oxygen come from? Certainly not the planet's crust, as it has been degassing for billions of years and is a depleted desert now. Hundreds of trillions of tons of material would have to be brought to Mars' surface. This is actually not as unreasonable as it may sound: comets can do (and have done) this in the past... but it would require a number of pretty large comets. A colliding planetary body from the Oort Cloud on the scale of Sedna could bring the mass as well as restart the magnetic dynamo, however. A collision like that is thought to be the reason why we still have a magnetic field here on Earth... and a Moon as big as the one we have.

A final assumption is also necessary: a weaker planetary gravity field would make it easier for gases to escape the planet. So another assumption would be that somehow the planet became much more dense. A comet impact couldn't solve this one. A collision with something like Sedna would only marginally increase the gravity field of the planet. Weak gravity -> easier for atmospheric gases to escape.

I'm not a specialist in atmospheric dynamics, so I don't want to speculate what would happen if all three of these conditions were somehow met. I suspect that Mars' currently pink sky might end up a different color, however.

Q: Thanks for the thoughtful reply Jeff, I appreciate you taking the time.  The thrust behind my question was basically to get an understanding of the scale of the terraforming humans have engineered on Earth and what the impact would be if that same process was applied to another planet of similar size.  I guess looking back I should have simply asked what the impact might be of 'magically' pumping 7,000 million metric tons of  carbon dioxide into the Martian atmosphere every year (7000 million metric tons being an approximate average volume created by human factors on Earth).  Thanks again and enjoy your weekend!

 -Kyle

A: Yes, I was fascinated by the book Dune and the movie Total Recall, but the physicist in me kept slapping me on the back of the head: There's no evidence of sequestered carbon on Mars except frozen CO2 at the poles. There is only rare (indirect) evidence of water - it's a desert world. Water being low density, it would be hard to hide it on a planet like Mars or Arrakis. THAT said, I participated in several expeditions across the Empty Quarter of Saudi Arabia. Ambient humidity there is about 2% (in an Arizona summer it is around 20%). It is so dry that you have to "snuff" a handful of water every hour all night long because your mucous membranes are on fire - and cracking from the desiccation. However, I did some geo-electrical soundings along our two routes to the Wabar Impact site and found evidence of conductors - probably above-bedrock water - in several locations at about 60 - 100 meter depths.

Why do I Need a Geologist in Order to Build my Deck?

Most of what the geoscience community does is profoundly practical. As you cross any bridge, enter any building, you have a professional geologist or engineering geologist  to thank for the fact that you are safe there. 

Q: I would like to extend (cantilever) my deck over my back slope. I am told by construction contractor that I will need a geologist to determine type of bedrock and/or soil and determine the depth required for installment of support piers (caissons) to support deck structure.

    Do I need to hire only a geologist for determining whether hillside slope will support a deck?

- Walter H

A: Laws and codes are different for different cities and in different states, and are different for flat or hilly ground, hurricane-, tornado-, or earthquake-prone terrains,  so I cannot directly answer this question. Some states require assessments by someone who has passed qualifying tests, and can designate "PG" (for professional geologist) after their name. Some states require an engineering geologist to do this sort of job. These people basically provide crucial experience and data to ensure conformance with local building codes. 

    I can indirectly answer your question by sharing my own experience, which may or may not be relevant. I chose a home with a great territorial view. The price I must pay for this view is that the home is built on a slope, of course. Any slope - especially something graded within the past 20-50 years and not already covered with semi-mature trees, is inherently unstable. For instance, after just ten years I had to pay for a rock retaining wall to be built at the bottom of my back yard/slope - because the soil was slowly creeping downward and had already buried my neighbor's fence 20 cm deep. In this area there are known/mapped slow or creeping landslides, also. On one public trail that I often walk, you can see hundreds of trees that are bent almost horizontal at the base, and then curve to vertical as they go up - a sure sign of a slow or creeping landslide.

    As part of the negotiation for my new house, the company selling it agreed to build a deck in the back. The distance from my bedroom door to the ground at that time was about 15 meters. That's a long first step if you are sleep-walking, so local building code had required the outside of the door to be boarded. I had no idea what the real costs of the final deck were, but an engineer came twice to my door and apologized. First, that he would have to make it wider than my realtor had suggested - to meet code. Second, he would have to connect each of three decks by stairs - to meet code. It had to serve as a fire escape suitable for children. Then an excavator came in and dug a 2-meter-deep trench, a meter wide and the width of my house, behind the house. They set up molds and brought in a monster machine that looked like a Snuffelupagus, and poured 5 concrete cylinders a meter wide and 2 meters tall each. These were even more deeper anchored with some kind of rebar to about 3 meters below ground surface. They brought in a small grader that covered/filled in the trench. To the imposing concrete pylons they bolt-anchored five pressure-treated beams (several of them 15 meters long!). THEN they began building the deck. When I asked the builder why so much precaution (it seemed like massive over-kill to me), he said that building ANY deck on ANY slope was fraught with problems, and from experience this was the MINIMUM precautions they must take. These precautions were built right into the building code.

    “Precautions against what?" I asked.

    "Against your deck joining your neighbor's party," was the reply.

     In the 12 years since the deck was built (it remains stable) I have seen several things including the bent trees and my own sliding lower backyard slope that convince me he was correct. 

     So much for my theory that I could get away with a couple of cinder blocks with some posts standing on them and do it myself. 

Is Your Job Dangerous?

Q: For a school assignment, I was told to ask a geologist some questions that I have about volcanoes. Is your job dangerous?
- Malayah M

A: It CAN be dangerous. I've walked out the toe of an evolving lava flow from Kilauea volcano, and accidentally stepped directly on the magma several times. It damaged my boots. Surprisingly, it sounds like Rice Crispies when you pour milk over a bowl of this cereal. This is because the outer millimeter or so of the lava "freezes" in the colder air and flakes off - it's the sound of ultra-thin glass breaking continuously. 

Most volcanologists I know are or were personally acquainted with people who are now dead - killed by a volcanic eruption. These deaths usually involved a silica-rich volcano that exploded violently. They were visiting during a time of volcanic unrest, and the explosion happened so fast that it didn't give them time to get far enough away. This type of high-silica volcano tends to form stratocones, so you have an idea of its potential to cause great destruction just by looking at it. Think: Mount Fuji in Japan. Avachinskiy in Kamchatka. Mount St Helens in the United States (it was a nice cone before 1980).

As a result, the volcanolgists still living, whom I personally work with, have become very careful and cautious. They don't take unnecessary risks - but being a volcanologist almost by definition means you must take SOME risks. 

Q: What do you do when a volcano is showing restless activity, and you have predicted that it will erupt soon?

A: We notify public safety authorities at the first reliable hint that something might happen. We make it a practice to drill with them and review the possible things that can happen, ahead of time. When Mount St Helens erupted in 2004-2008 the interaction between the USGS volcanologists and the federal, state, and county safety authorities was almost seamless.

Q: Have you ever witnessed a volcano eruption??

A: Several times I've witnessed a volcanic eruption:
- Mutnovskiy volcano in Kamchatka erupted as I was inside the main caldera in 2004. Fortunately it was a mild eruption, but the Russians with us gave us no warning (I don't think they had realized what was happening before we did). 
- Kilauea has been erupting continuously since 1983, and I have visited the flow-front a number of times. There is an interesting photo here: https://profile.usgs.gov/jwynn - look in the upper right-hand corner. When you're near a lava-tube like that, the ground moans and quivers. It's truly eery, even unnerving.
- I was the first person to see and photograph the new dacite dome coming up from under the glacier at Mount St Helens on October 12, 2004. I was orbiting in a helicopter inside the crater at the time. There was steam everywhere, and the glacier was fissured almost to the point of crumbling. Then I saw something grayish-pink that was NOT ice. 

- In addition, I've been on several restless volcanoes that were showing activity like fumeroles and weak earthquakes (Mount Lassen, in California; Akutan in the Aleutian Chain, etc.).