Friday, December 11, 2015

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.




Wednesday, November 11, 2015

How To NOT Go Off-The-Wall Freakin' CRAZY...

...when a Cascadia Earthquake hits.

From personal experience, when a really big earthquake hits, it is extremely unnerving. In fact, my first earthquake was a magnitude 7.3 event in Southern California, and the serious shaking lasted not much more than 3 minutes.

However, it seemed like a lifetime to me then. If asked a week later, I probably would have said that it lasted at least a half an hour.

Look at the following diagram, taken from Wikipedia:



The P is what woke me up. It hit with a bang.
The S is what rattled and then broke the windows, and stutter-walked my bed 30 cm.
The R is what finally flipped me out of my bed and onto the floor.

It took several days for the information on this event to filter down through the scientists to the government entities, to the news media, to my parents, and then to me as a 6-yr-old child. By then we were back in our house, the power was restored, and we had water pressure again.

A Cascadia subduction earthquake might reach a moment magnitude 9+ when it next occurs. That will be at least 100 times more energy than the piddly 7.3 event that launched a sleepy 6-yr-old out of his bed in Bakersfield, California long ago. If I found a M=7.3 to be that terrifying, imagine how bad a M=9+ event will be.

There are two ways to deal with the terror:

#1. Understand immediately what is happening and what will come next.
#2. Be prepared for it. Know that you have your bases covered.

#2 is something that many people more or less do (some do OK, some do better, and some do extremely well at this):
A. Have a family plan in place. Where do we meet? What channels on the battery-powered, $40 hand-held walkie-talkies will we be using to find each other?
B. Have supplies at hand, including
    i. Food. And don't count your refrigerator contents here.
    ii. Water. A LOT more water than you might think.
    iii. A battery-or-crank-powered Radio
    iv. Batteries. Flashlights. LOTS of batteries.
    v. Blankets and sleeping bags, and/or a heat source to keep warm.
C. Start checking up on your neighbors, and offer to share your stuff with them. People you may hardly know will become life-long friends really quickly.

However, the purpose of THIS blog entry or chapter is to help you deal with #1: understand what in the world is going on, so you don't go crazy. 

Next, look at the following diagram:


This will help you to understand the TIMING difference between the several kinds of seismic waves. The P wave arrives with a bang, like someone with a large hammer just whacked one side of your house. The S wave will feel different: slewing everything back and forth, perpendicular to a line between you and the epicenter of the earthquake. The R (which stands for Raleigh, or surface) waves will feel to you like you are in a small skiff after a large boat roars past, careless of his wake. You will feel like you are rolling around, up and down, and sideways . You always end up pretty much in the same place with each complete roll. 

All these things are important clues for you. This is what you do:

FIRST: as soon as the P-wave hits, look at your watch... which we both hope includes a second hand.

Second: as soon as the S-wave hits, think about what direction is PERPENDICULAR to that sickening side-to-side motion: this gives you the important clue as to where this thing is coming from. If the slewing motion is north-south, then the earthquake epicenter is either east or (more likely in this case) west of you.

Third: as soon as the S-wave hits, look at your watch again. Subtract the P-wave arrival time in seconds from the S-wave arrival time. That difference tells you how far away the hypocenter (the actual sub-seafloor rock rupture) is from you.

Use the following diagram to convert that P-S time difference into a distance::


Fourth: KEEP TRACK OF THE TIME even after you have this number. If the event is a M=9+ event, the ground will keep shaking and heaving for a full 5 - 6 minutes. THIS will give you a sense of how bad things will be in the following several weeks. If it was just a segment of the Cascadia Subduction Fault breaking, then the time could be as little as 3 - 4 minutes. This is GOOD. If the heaving and shaking runs up to 6 minutes... well, you already have #2 above in place, right? So you are prepared.

This will help: If you live in Portland or Seattle, and the P-S time difference is 20 - 45 seconds, then the event is far enough away (or close enough, depending on your point of view) to be The Big One: A Cascadia Subduction Event. 

But YOU WILL ALREADY UNDERSTAND WHAT IS GOING ON even before the first news reports start coming in (assuming you have a flashlight close and a battery-powered radio on hand). 

AND YOU HAVE YOUR PREPARATIONS IN PLACE. 

And no, you are not crazy: you are informed and prepared. 



Friday, October 30, 2015

The Coast is Toast

When I was a child the White Wolf Fault, a splay-fault of the great San Andreas, ruptured about 60 km (40 miles) from my home. I recall hearing a bang, then hearing the windows rattling hard - and finally breaking. Shortly afterwards, I was thrown out of bed onto the floor. I didn't fall out of bed, I was thrown from my bed to the middle of my bedroom floor. When my mother called to me from her bedroom to come to her (she was trying to hold onto her own bed at the time), she told me that I replied "I can't. The walls keep hitting me." On our hands and knees we finally made it as a small family out to our back yard (my Mom was fearful of the gas line rupturing and suffocating or burning us all). This earthquake had a moment magnitude of about 7.3

The movie "Volcano" made the expression "The Coast Is Toast" famous. "Volcano" postulated a volcano somehow under the San Andreas Fault. When the film came out, my volcanologist colleagues cringed. While volcanoes ARE associated with faults, they are associated with deep subduction faults, where ocean floor is over-run by a continent in what is called a thrust fault. Think of the Cascades range, far inboard from the Cascadia subduction fault 50 - 100 kilometers offshore. The volcanoes themselves are found far inland from where the huge subduction fault reaches the ocean floor.



However, the expression "The Coast IS Toast" is not that far off the mark in the sense of massive destruction that could visit the Pacific Northwest coast if and when a Cascadia subduction event occurs. It could be a magnitude of 9.0 or higher - this would represent over 100 times more energy released that what woke me up years ago.



The Cascadia Subduction Zone (CSZ) is just that: a plate-subduction thrust fault spread over 1,000 kilometer length, extending from offshore Vancouver Island in Canada to offshore northern California. It's width depends on what you count, but earthquake imaging of the down-going oceanic slab extends well into central Washington and Oregon. Three major oceanic floor plates, the largest being the Juan de Fuca, are being over-ridden by a westward-moving North American continent. Part of the thrust fault is lubricated by the ocean-floor sediments atop the Juan de Fuca plate, and part of the down-going slab is partially melting in the upper Mantle, giving rise to that almost linear string of Cascades volcanoes. These volcanoes extend from Mt Garibaldi in British Columbia to Mount Shasta and Mount Lassen in Northern California.

But in between these parts is a segment, extending the entire length of the fault zone, that is stuck. The lubricating fluids have been squeezed out by pressure with increasing depth, and the stuck part is like a dry patch in the center of your hands as you try to slide one past the other. THIS is where the the rub lies, so to speak. In 2004 a similar subduction fault near Aceh in western Indonesia ruptured, creating a magnitude 9.3 earthquake. The tsunami alone killed over 250,000 people around the Indian Ocean as far away as Mozambique. When a similar subduction fault offshore of northern Japan ruptured in 2011, the surface area of the fault that was displaced or ripped was enormous: 300 kilometers long by 200 kilometers down-dip. This is important, because the surface area ruptured correlates closely with the energy released. "Down-dip" on the San Andreas Fault is only about 10 kilometers - because this fault is more or less vertical, and the rock becomes plastic at about 10 kilometers depth.

There is a security camera video of a 15-meter (50') wave breaching the 5-meter (16 ft) tsunami-protection walls of the Fukushima Dai-Ichi nuclear power plant on the coast. If you've been trying to body-board in the ocean, you know how hard a 2 meter (6 foot) wave can slam you. To state the obvious, you don't just stand your ground with even this small a wave: water is nearly as dense as your body. The estimated cost of this disaster to Japan as a nation is now in excess of $300 billion.

That sounds unimaginable. However, a Cascadia Subduction event is a very real, in fact inevitable, likelihood for the Pacific Northwest.

What will happen when this inexorable event occurs?

The coast will lurch westward 20 meters (60 feet)... and remain there permanently.

The coast will drop down on average 2 meters (6 feet)... and the low-lying parts will remain sunken permanently.

A tsunami up to 40 meters (130 feet) tall will strike coastal communities in as little as 15 minutes from the onset of the first shaking.

There will be fires that are unstoppable - because gas mains and water mains will both be ruptured. The 1906 earthquake in San Francisco was over in probably less than 3 minutes... but the fires that destroyed nearly ALL of San Francisco raged for four days afterwards. The fire department at the time was helpless. 

In the Pacific Northwest, emergency planners have estimated that 10,000 people will die, and another 30,000 people will be seriously injured.

The closer to the epicenter - a broad north-south line just off and beneath the coast - the greater the damage. The farther east you live, the greater the attenuation of the energy released by a CSZ event. Attenuation means the Earth's crust in between the fault and, say, Yakima, Washington, will absorb most of the radiating seismic energy. 

But first, the ground will first jerk westward, then begin going up and down and sideways, then begin rolling. This will go on for 4 - 6 minutes...

It will definitely wake you up. From experience, I can tell you that it seems to go on forever.

How often does Cascadia's fault rupture? An early study of bouma sequences (mud layering in deep-ocean coring) suggested 7 events in the past 3,500 years, but a recent report by Oregon State University suggests that the average time between major earthquake events may be as little as every 240 years. When was the last one?

January 1700 AD.

This event gave rise to the Orphan Tsunami in Japan, so-called because there was no felt earthquake nor approaching typhoon to provide warning before enormous waves suddenly appeared and obliterated or damaged many fishing villages along the Sendai coast. That's over 300 years ago. This is somewhat simplified, of course, because the CSZ cannot really be treated as a single entity that always behaves along its entire length the same way. Detailed geologic mapping, in fact, suggests that there are sometimes separate ruptures along the "northern zone" and the "southern zone"... 'mere' magnitude 8.5 events.

But make no mistake: while a magnitude 8+ event may feel different from a magnitude 9.0 full-rip event (lasting "only" 4-5 minutes instead of 6), there will still be widespread damage.

The event spacing (the average of 240 years vs. the current hiatus of 315 years) suggests we are then "overdue", doesn't it? Not necessarily, because the spacing between previous events has been as much as 500 years. Earthquakes do not click along like clocks. In fact, we cannot predict earthquakes unless we are injecting water into wells in a tectonic region like the area north of Denver, CO. For all large earthquakes, despite upwards of $100 billion spent on research over the past century, the best minds I personally know unequivocally say that current science cannot predict when an earthquake will happen.

But scientists can forecast major earthquakes. That's a very different thing than a prediction. This means that scientists can say, based on existing data, that there is a 40% chance of another Cascadia event in the next 50 years. So... less than a 1% chance in the next year. Buy earthquake insurance or not?

What can that plausibly mean to you - realistically, practically? What can you possibly do with this information?

First, scientists CAN make reasonable estimates of what will happen during and after a Cascadia event, and you and I CAN prepare for those. This is going on right now in local and state organizations in the Pacific Northwest. Infrastructure is being examined with an eye towards what can be reinforced. Building codes have already been upgraded - then upgraded again - to help us create new roads, bridges, and buildings that will better survive such an event. There are estimates in Oregon, for instance, that a majority of bridges will be compromised or fail on coastal US Highway 101, and at least five bridges on inland interstate I-5 will fail in Oregon alone. The damage will be worse the closer one is to the coast, but in both instances it takes just one bridge in a strategic location to shut down interstate commerce. Don't count on being able to find food on the shelves of your local supermarket for awhile... or even count on being able to GET to your supermarket. Repairs to powerlines, gas lines, roads, bridges, etc. will take time. They will happen sooner inland, and take longer in the coastal communities.

This means you should have at least 2 - 4 weeks worth of non-perishable food for each adult in your household. You should have at least two gallons of water, per day, per adult, enough to last you that whole time. A majority of people planning for a disaster forget about the water part - it's raining all the time in the "Pacific NorthWet", isn't it? You should also have batteries - LOTS of batteries. A hand-crank radio will be very helpful, perhaps a lifeline.

Most important of all, you need to have a family plan for dealing with this - or any other catastrophe. In the short term, only you can help your family and your neighbors. It will take awhile for the country as a whole to martial the necessary resources to even partially help.

If the example of Hurricane Katrina can be used, yes, we will recover. However, the recovery effort will consume much of the region's GDP, and it may be more than a decade before everything is running as smoothly as before the event. New Orleans and Memphis, TN, had similar economic output in 2005. Today New Orleans still has not caught up with Memphis.

We will survive. We will rebuild. We will be toast only if we refuse to do anything.



Friday, October 23, 2015

Why do I Need a Geologist 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. 

Saturday, October 3, 2015

Gold and Lava

This ask-a-Geologist query began as a science fiction writer trying to make his novel more realistic. His original question was framed around a scene where gold is mixed in a lava flow. Barring the obvious difficulties of how you would (a) concentrate and refine the gold and (b) why would you want to play with gold in a lava flow in the first place...

           Q: Does the gold just melt completely away? Would It sink? Would it meld into the Lava and you couldn't tell the different between the two? Would it rest on top and be visibly different? I'm writing a story and I want to be as scientifically accurate as possible. And considering I don't know what happens when Molten Lava touches a refined Precious metal. I thought i would ask.

– Jeremy A

A: To start with, your hypothesis is a long way removed from any possible reality. This is because gold is rarely found in nature in a form larger than tiny flakes. The rare nugget found in Alaska is just that: extremely rare, and secondary at that (i.e., the nugget is not the original form).

            If you want to modify your story to deal with a refined gold artifact, the following may be helpful:

            The melting temperature of pure, refined gold is 1064 °C. By comparison, the melting point of magma is in the range 700 °C to 1300 °C - depending on its silica content. Gold is also extremely conductive, both electrically and thermally. Gold will thus tend to conduct heat through it very efficiently. 

            The density of pure refined gold is quite high: 19.3 g/cc. A typical magma might range in density from 2.4 g/cc to 3.35 g/cc - again depending on silica content. 

            From these, I can suggest two possible scenarios:

1. If a refined gold object is set on an active flow down-range from Kilauea/Pu'u O'o (on the Big Island, Hawai'i), it will initially start to sink into the magma. Experience has shown (including my personal experience) that magma exposed to air quickly forms a crust and hardens inward - rapidly - from that crust. I've personally walked over active toes of magma flows there, because it was already crusting over. And yes, it was still rough on my boot-soles, but mainly because the crust is really mostly glass. Under these very specific circumstances, the gold object would end up being locked, partially sunk, in the cooling magma crust. 

2. In another possible scenario, the refined gold object might be thrown into an active lava tube (look at the photo in the upper right of this link: https://profile.usgs.gov/jwynn for an example of a skylight broken into a lava tube). In this case, the magma temperature is in the 1200 - 1300 °C range, and the gold object would first sink, then slowly turn liquid and begin to disperse in the magma as it continues down the lava tube. 

Hope this helps your book be a bit more realistic.
~~~~~
 

Saturday, September 19, 2015

Age of the Earth in a Nutshell



Q: In geology class my professor told me that the earth's age is based of off meters how does this work
Thanks for your help
- Theo

A: 

The age of the Earth was initially estimated by scientists by mapping stacks of sedimentary rocks in the UK, then measuring sedimentation rates in similar environments (lakes, rivers, seashore, etc.). In the 19th Century this initially gave startling - even shocking at the time - estimates in the hundreds of millions of years range. In the early 20th Century radioisotopes became available, and these were used to extend the age of the Earth into the billions (billion = thousand million) of years age range*. This physically meant measuring back to the point in time when the mineral hosting the radioisotopes and their daughter-products was last melted. THEN it just became a game of searching all over the Earth for the oldest date-able minerals with uranium and lead in them (for example, a zircon crystal). The oldest rocks found so far are in Greenland and western Australia, and based on these the Earth's age is estimated to be at least 4.55 thousand million years old. This means it is at LEAST that old. 

* Note that in some countries like the US, the word "billion" means a thousand million, while in other countries (e.g., the UK), the word "billion" means a million million.

Monday, September 14, 2015

Paleomagnetism

Paleomagnetism = old + magnetism
It's the study of magnetic signatures in ancient rocks, and what they can tell us about the Earth long ago. This requires drilling out little core samples from rock outcrops, carefully marking them for orientation, then back in a laboratory measuring the orientation of the remnant magnetic field that comes from just the rock itself.

Q: Could you tell me what factors they looked at to determine that the north pole moved.

My book says it left markers but i couldn't find what markers it was referring to.
- Theo


A: There are magnetic minerals in most non-sedimentary rocks including, most commonly, magnetite. Each individual iron-containing mineral crystal grain has a magnetic moment - sort of like a tiny bar magnet - frozen in the orientation direction of the Earth's magnetic field at the time that the mineral solidified out of its original melt. This is called remnant magnetization. In an unweathered igneous rock, these tiny magnetic domains (if there are magnetic minerals in the rock) will all align in the same direction as the Earth's field. A fluxgate magnetometer can be used in the field to orient the sensor until it aligns with the rock's internal magnetic field. Geologists can use these to tell the difference between apparently similar volcanic flows in the field, just by the different remnant magnetic fields in the different flows.

In a sedimentary rock these magnetic domains will usually be randomly oriented, because the mineral grains have been jumble up as they were wind blown or washed down a stream. 


The geology sub-field of paleomagnetism is the study of how these orientations can depict the Earth's magnetic field at times in the past - but of course this means that you must also be able to date the rocks. After more than a half century of gathering data, paleomagnetic specialists can say definitively that there have been magnetic epochs when the Earth's magnetic poles were oriented just like it is now - and epochs when the magnetic field orientation has been reversed. Of intense interest in the geoscience world right now is refining the dating part, in order to see how *fast* the Earth's magnetic field orientation changes or flips over when it does. Does the orientation of the magnetic field flip overnight, or does it take 100,000 years? The difference is important.

During that switch-over time, our planet doesn't have the magnetic protection from energetic charged particles from the Sun like it normally does (these charged particles being deflected by the Earth's magnetic field are what creates the auroras). The implication here is that there will be a lot more radiation damage to creatures living on the Earth's surface during a magnetic pole switch-over transition time. The next implication: perhaps this equates with (a) a jump in biological diversity, and/or (b) a dying off of some species. 
~~~~~
 

Friday, June 12, 2015

Porosity in Sandstone and Carbonate Rocks

Q: Dear Sir, I would like to ask what are the classification of porosity in carbonate rocks?
- Tarek M

A: Carbonate rock porosity is a very big issue in the oil and gas world – perhaps THE issue. Water, gas, and oil must be able to move through the rocks or there is no oil and gas business. The nature of porosity in a source or reservoir rock can make all the difference in whether the hydrocarbons can be formed in the first place, and later economically extracted or not. Basically, can the oil mature and be concentrated in the first place – and if so, can it later then be extracted?

Here are some links that might help answer this for you:
http://pubs.usgs.gov/wri/1994/4013/report.pdf
http://www.slb.com/services/technical_challenges/carbonates/near_wellbore/rock_properties.aspx
http://en.wikipedia.org/wiki/Porosity
http://www.searchanddiscovery.com/documents/2004/mazzullo/images/mazzullo

        By comparison, sandstone porosity is pretty simple: it consists primarily of inter-grain spaces.

For carbonates (e.g., limestones and dolomites) however, porosity evolves with time and can be quite complex. Porosity in carbonate rocks is thus usually classified on the basis of the timing of the porosity: how the porosity changes and develops over time. Perhaps surprisingly, porosity often evolves over time. First, there is primary or depositional porosity, in which the pores are inherent in the newly deposited sediments and the particles that make them up. These pore types include inter-particle pores in carbonate sands (muddy or otherwise), and intra-particle pores (i.e., small passageways within tiny fossils such as foraminifera). Another pore type is fenestral: these are pores formed by gas bubbles and sediment shrinkage in tidal-flat carbonates, and also the growth-framework or structural pores common in reef buildups.

        In carbonate rocks (as opposed to sandstone) you can also have secondary pores – in other words pores that form as a result of later, generally post-depositional dissolution of certain constituent minerals. You can also have vugs: large pores that cut across the rock fabric. This means that the dissolution has not been controlled or driven by the fabric of the original deposition. Incidentally, you can also have pores that are basically dissolution-enlarged fractures. The natural tendency in most carbonate sediments is to for groundwater to cement in and overlying rock pressure to compact the pores during post-depositional burial. Most geologists believe that the bulk of the porosity in limestone and dolomite reservoirs is secondary in origin: post depositional, in other words.

Keep in mind in this discussion that carbonates and sandstones are discrete members of what is usually a continuum of rocks types in a stack of sediments. One can encounter sandstones, limestones, anhydrites, shales, and dolomite in relatively close proximity in a sedimentary package.

Saturday, June 6, 2015

Hey! A Sedimentary Rock Looks Like an Igneous Rock!

Q: I encountered a sedimentary rock in lab called Greywacke and it reminded me of an igneous rock, Gabbro. How does one differentiate these 2 apart? Or basically igneous from sedimentary and vice versa.
- Feiruz R


A: Igneous rocks were formed when the material was a melt, so the individual mineral grains are tightly fused and intergrown, and the porosity in the rock is very low. A greywacke was formed by accumulation of cold, weathered detrital material. It might superficially LOOK like an igneous rock, but a porosity test would give it away immediately. A closer examination with a hand-lens will show angular grains in a greywacke that do not interlock seamlessly; the word "greywacke" means that this rock also includes very fine silt, so this tends to fill those inter-grain boundaries between the larger crystals - but with a hand-lens you can see this. A petrographic microscope makes it even more obvious that a greywacke is really a garbage can term, representing an accumulation of weathered material of all different grain sizes. 

Saturday, May 30, 2015

Oxygen and Mcrobes and Algae and the Early Earth

Q: Hi!
Oxygen in our atmosphere was created by small creatures who had just invented a new process:  photosynthesis.
The waste product of photosynthesis is oxygen.
After an unfathomable number of  years, too much O2 built up in the atmosphere, changing the greenhouse gas, methane, into carbon dioxide, which isn’t such a strong greenhouse gas.  This caused the earth to cool off to the point where the first known ice age began, the huronic, I think.  It lasted for millions of years and enveloped the entire earth with ice.
Question 1: how did these photosynthetic creatures survive in an iced-over earth?
Question 2: what caused the end of this very long ice age?
 Just curious - Thank you!
 - Susan K

A: Your question suggests you are well along in studying this topic. I've stored a number of closely related questions and answers on this blog, and by way of a long answer, some of these may help:

http://askageologist.blogspot.com/2013/07/climate-change-is-it-real.html
http://askageologist.blogspot.com/2013/04/castastrophes-and-mass-extinctions.html
http://askageologist.blogspot.com/2012/06/snowball-earth-faint-young-sun-paradox.html

The medium-length answer: Our atmosphere passed through the oxygenation transition around 2.5 billion years ago, and it certainly involved photosynthesis - stromatolites (fossil algal clumps) have been found dating as far back as 3.3 billion years. However, there are also suggestions that mantle outgassing, tectonics, and oceanic current-shifts may have contributed. There really was a Snowball Earth episode, and there have been a series of cold-warm cycles since then. Scientists have been exploring - with limited data - what could have caused these events, and suggestions range from the fairly mundane to the exotic: asteroid impact, tectonic change that interrupted oceanic current flows, etc. The Chicxulub asteroid event 65 million years ago certainly knocked the oxygen levels in the atmosphere down dramatically, requiring millions of years to recover. This is almost certainly why bar-headed geese can easily fly over Mount Everest: birds have evolved a truly advanced respiratory system since that event. Evolution is well-documented to speed up under environmental stress.

Some short answers:
1. If there is one thing certain about microbial life, it is that it can survive almost anything. Microbes have been found kilometers deep in the Earth, and temperatures steadily increase with depth due to radio-isotope decay in the Mantle and Core of the Earth (the temperature rises to typically 60 C at 4,000 meters depth).


2. There are a lot of variables that may have been involved in the recurring cool-warming cycles, including the fact that the Sun has steadily grown in luminosity during its lifetime, as well as tectonics, and methane-emitting life forms. Likely a combination of these - and probably other factors - led to out-of-control feedback loops that dead-ended in climate extremes before the atmosphere eventually  recovered. 

Saturday, May 23, 2015

Damage Earthquakes Cause


Q: What kind of damage can a(n) earthquake do?
- Carrera K

A: Earthquake damage can be very wide-ranging. In increasing order of destructiveness (roughly following magnitudes from M ~4 to M ~ 8) :

1. Small cracks form in drywall, stucco, and concrete walls of buildings.

2. Fragments of building fall into the surrounding streets - glass, or bricks from the corners of windows, etc.

3. Topographic settling, leading to serious internal structural damage in buildings, making them uninhabitable (San Francisco, Loma Prieta earthquake, 1979).

4. Large fractures form in soils and rocks. Water towers fail. Electric power is cut and gas lines rupture (White Wolf Fault, Bakersfield, CA, 1952).

5. Major fires start that are difficult or impossible to control (San Francisco, 1906 AD).

6. Collapse of concrete floors in buildings, crushing most of what lies within (Izmir, Turkey, 1999 and 2013).

7. Major infrastructure collapse, leading to water-borne diseases, and starvation happens on a wide scale (Haiti, 2010).

8. Tsunamis wreak broad damage to coastlines, killing most people within reach of the water (Aceh, Indonesia, 2004).

9. Allocthons and major landslides cover or sweep inhabited regions. Segments of coastline drop below sea level (Puget Sound, 1700 AD), and rivers temporarily reverse direction (Mississippi River, 1811).


10. Entire civilizations collapse and do not recover (the Minoan civilization, 1,500 BC, though how much was explosive volcanism and how much was caused by earthquake damage is unclear). 

Sunday, April 19, 2015

Ethics & Conflicts of Interest - No Private Work in Minerals

This Q&A actually raises an important issue, which at its core involves ethics, and conflicts of interest in science. The US Geological Survey was established in 1879, but an important event in 1871-72 led to its creation. An unscrupulous Kentucky con man tried to sell a worthless mining property to some gullible investors in San Francisco. After he staked a claim on federal land, he “salted” the property with rough diamonds that he had apparently stolen from a drill-bit manufacturer that had employed him. He apparently thought that he could fool some greedy investors who would not look beyond the few diamonds and other rough gems that they saw at the surface. The investors were nearly taken to the cleaners, and the con man eventually made off with what in today’s money would be $8 million.

However, a young, Yale-educated geologist named Clarence King had been funded by Congress to assess the huge federal lands that Congress had responsibility for in the Western United States. King was aware of the news of the “great discovery” – actually one of a long list of scams and get-rich schemes common at the time in what was truly a Wild Wild West. Putting two and two together from the partial information the con man had released, King and his party located the claims in a remote part of Colorado. It didn’t take long to tick off the obvious evidence (diamonds were only found at the surface where there were already footprints, and none were found below in trenches that they dug to test the local soils, etc.). As their field investigation concluded, King and his party discovered that they had been spied on for days by a New York diamond dealer who had secretly followed them and who had been watching with a telescope from a nearby butte. When someone from the party blurted out that the discovery was a giant hoax, this man exclaimed “What a chance to sell short on the stock!” Stung at hearing of this obviously unethical plan, King raced back to San Francisco to beat him, and informed the wealthy investors about what had been going on. He was greeted as a savior. The San Francisco Bulletin wrote “Fortunately for the good name of San Francisco and the State, there was one cool-headed man of scientific education who esteemed it his duty to investigate the matter in the only right way.”

Read more here: http://www.smithsonianmag.com/history/the-great-diamond-hoax-of-1872-2630188/#wt4lHMrIiH1XwdM7.99

In part because of this success, in 1879 King became the first Director of the newly-formed US Geological Survey. From the very beginning, ethics and integrity were built into its policy and operation. Today a USGS employee and even family members are not permitted to hold stocks or any other interest in a natural resource or a related company. It’s not a great reach beyond this to ensure that no federal employee uses skills and facilities to help a private individual while on the tax payers payroll. At the core of the USGS Fundamental Science Practices policy we find these words “The scientific reputation of the U.S. Geological Survey (USGS) for excellence, integrity, and objectivity is one of the Bureau’s most important assets. This reputation for reliable science brings authority to data and findings, creates and protects long-term credibility, and ensures that the public trust is met.” (May 24, 2006). I find great personal satisfaction in belonging to an organization that treats integrity and excellence as its most valuable assets.

Q: I know u probably get this alot. My name is arial. I am sure i found a precious gem deposit in georgia. I know that if it is this is an incredible find. I cannot find anyone who can or will test the stones. I have done all the research and i do have possion of the stones. I removed them feom the rock myself. If u are interested in the least bit i can show u the samples and the location from where they came. Thank you
- Arial L

A: I am so sorry, but my volunteer work for Ask-a-Geologist prohibits me from getting involved in anything like a private gemstone or mine evaluation. It's actually built into the Organic Law which started the US Geological Survey in 1879 - I would be breaking that federal law. 

Our work here is closely guided by specific Congressional mandates (for instance in my office we monitor potentially active volcanoes), and we are not supposed to do anything outside our mandate. We are very much aware that the US taxpayer is paying for what we do, and we try very hard to be as efficient and careful as possible with that trust. 

We are ESPECIALLY prohibited from doing ANYTHING that could possibly be construed at helping a single individual or group of individuals with a mineral deposit, or in a way that could financially benefit an individual or group of individuals. This is viewed as using taxpayer funds to promote something for someone other than the country as a whole - a form of corruption. 

My recommendation is that you contact the Georgia Geological Survey (note the mineral resource maps in this link: http://epd.georgia.gov/georgia-geologic-survey-maps), or talk with a member of the department of geology at the University of Georgia or Georgia State University. 

Sorry I can't be of more help than this.

Q: Avtually uve helped alot by letting me know who to contact thank you.  Ariel

Friday, April 10, 2015

Will The Plate We Live On Sink? More Tectonics Questions.

Q: Dear Geologist, we are students from the Schiller Gynasium in Berlin and we would like to ask you some questions about platetectonics.
- Emma and Lili K

A: Hi, Emma and Lili,
My grandmother and her family came from Bavaria (Goggingen/Augsburg), so I have a soft place in my heart for Germany. I'll try to answer your questions in order below: 

Q: Is it possible that the plates we live on are going to sink?

A: The plates we live on will not sink. They have a higher silica content than the Earth as a whole and are thus less dense (average density of 2.67 grams/cc), so they float on the denser Mantle material. The plates that DO sink during subduction tectonics are ocean floor segments. These plates are made of  injected Mantle material that comes in at ocean floor spreading centers like the Mid-Atlantic Ridge. This material has more iron, magnesium, and calcium, so it is usually more dense (average density about 3.2 grams/cc or even higher). When these ocean floor segments meet continental crust in normal plate tectonic collisions, the ocean floor segment is usually - but not always – over-ridden. There are rare instances where segments of oceanic crust are rafted onto continental margins by this messy collision process, and these are called ophiolites. Examples are in Cyprus (the Troodos ophiolite), Oman (the Semail Ophiolite) and northern California, USA (the Josephine Complex). These ophioloites are fascinating to study, and often host pods of dense chromite (more than 7 grams/cc) in them. A chromite pod the size of a large room may be worth over a million dollars/euros.

Q: Can the mantle and the outer core mix (as they are both liquid)?

A: The Mantle and outer Core are indeed liquid according to seismic refraction studies, but they have already been largely segregated by gravity over the last 4 billion years or so. If there is mixing, it is local in nature. Some laboratory studies and modeling suggest that the outer core is actually growing, as the gravity segregation apparently is still continuing. 

Q: Would it be possible that the pangea forms again?

A: Yes, it is possible to have another super-continent like Pangaea, as the Pacific continues to narrow on almost all margins. However, it will take hundreds of millions of years to accomplish this. It will likely not be a clean recombination, but more likely a complex amalgamation of crustal segments and fragments. The Atlantic opened up once before, then closed again, and then opened again a second time. It is now widening at the Mid-Atlantic Ridge, so the Atlantic grows while the Pacific narrows. As the history of the Atlantic Ocean shows, this may change at any time in the future.

Q: Thank you for taking time to read our e-mail!

A: I'm glad to help. You will perhaps be the next generation of Earth scientists, and discover things that we don't know about today. 

Friday, April 3, 2015

Ever Been in an Earthquake?

Q:  Have you ever been in a earthquake
--Gretchen H

A:  Yes, I have "been in a earthquake". As a 6-year-old I was thrown out of my bed by a M=7.2 earthquake in Bakersfield, CA, that hit at 3:30 in the morning. My Mom told me later that she called to me to come to her bedroom down the hallway, and that I answered her "I can't. The walls keep hitting me." These were probably the manifestation of Raleigh or surface waves rolling through the ground beneath the house. I do remember standing in the grass outside the house later and listening to sirens until dawn, as the adults talked about what had happened. That's where I first heard the word "earthquake."
    I also felt several earthquakes when I lived for three years in southern Venezuela. One event frightened the other residents of our apartment building so much that they all ran down the stairwell and stood in the street outside.
    You have to be physically in contact with the ground to feel small earthquakes. If you are driving a car or sleeping in a soft bed you may not feel events up to a magnitude of 3 or 4. 

Q: Thanks so much for answering my question.  I bet it felt very scary in the earthquake.

A: The experience wasn't so scary as it was a sleepy mind trying to figure out what was going on. That part took me awhile as a six-year-old. Then it was just sort of being amazed and listening to adults try to explain it as THEY were figuring it out. I remember my Mom, being very frightened, going down into a darkened basement to shut off the natural gas. I felt her fear then, my first fear, mainly for her.