Friday, July 7, 2017

Where did this rock come from... and, uh... is it legal?



There are rock and mineral shows all over the world, and for a price you can acquire a gorgeous Trilobyte fossil, a stunning Epidote crystal, or a piece of a meteorite. However, if the vendor sells you something but is unwilling to provide its provenance - where it came from - it is probably wise to get suspicious. 

Kilauea volcano in Hawai'i is a case in point. It's a National Park, and it's illegal to take any volcanic sample unless you have a legitimate research permit (which the US Geological Survey has, but still uses only sparingly). Imagine if every tourist hauled away 5 kilos of lava. With hundreds of thousands of tourists over time this has a significant effect - causing visible damage to a National Park. The US Post Office at Volcano, Hawai'i, has a back yard pile of volcanic lava. They have all been mailed back by guilty people, after they surreptitiously collected a sample and took it back to Iowa... Hundreds to thousands of kilos of lava are returned each year. This may also have something to do with Pele's Curse - there are ubiquitous warnings that the volcano goddess Pele will curse anyone taking part of her away. When bad things happen to someone (bad things happen to everyone), then some people may feel it must be because they did something wrong. 

This problem is far worse with archeological sites and African wildlife. As a general rule, it's unwise to buy any archeological artifact, or any ivory, because the likelihood that it has been legally obtained is vanishingly small. Archeological looters - grave robbers - operate with different degrees of impunity all over the world. There are laws against looting burials in most countries, but they are difficult to enforce, and many ancient cemeteries are littered with crude potholes. Priceless information is lost this way - not to mention who wants their grave dug up for trinkets? It's not unlike the ongoing massacre of elephants and rhinos in Africa, done to satisfy the insatiable demand of wealthy clients in Asia and the Middle East. 

If you have doubts - then it's probably wrong.

Q: I just purchased a volcanic bomb that was from somewhere in Alaska. I'm trying to identify which volcano it may be from. Any idea on how to narrow possibilities. Its a lovely piece but my "organized self"  would like to put a label on it as to source... if possible. So far I have Mt. Aniakchak but assume it could be one of a number of choices.
- Frank S

A: 

The only reliable way to know the provenance of a rock sample is from the person you purchased it from. That, I would think, would be a minimum requirement to sell something like this. In the past I've bought Trilobites from Morocco, and several fragments of iron-nickel asteroids at rock and mineral shows (and a tiny piece of one Nakhlite from Mars), but I would not consider buying them if I didn't know where they were acquired - that's in part because I'm a geoscientist and want to understand things. However, it is also in part because I don't want to contribute to a serious looting problem:



There is the possibility that your volcanic bomb was acquired on federal land or private land that the seller couldn't legally poach from, and that may explain the reticence to provide a specific source. People who sell fossils, mineral samples, and meteorites at rock and mineral shows are always very careful to provide provenance as a way to protect themselves from prosecution. 



Generally, to provenance an unknown-source rock requires a careful comparative isotopic and petrographic analysis - this is how experts learned that the two-to-four-ton Preseli "bluestones" from the third construction phase Stonehenge came from Wales, 250 kilometers away, for instance. 
~~~~~



Friday, June 2, 2017

General Planetary Geology Q&A

Q: To Whom It May Concern
I’m not a scientist, however I find it an interesting issue.
I have a few questions of which I hope you can clarify for me:
- Preben P
A: I'll try to respond to each of your questions below in CAPS:

Q: 1: How does the inner core of the earth maintain its temperature? Or is it decreasing?
A: FOR ONE THING, THE CORE OF THE EARTH IS WELL INSULATED WITH VAST VOLUMES OF LOW-THERMAL-CONDUCTIVITY OVERLYING ROCK. EVEN WITH CONVECTION IN THE MANTLE (AND PERHAPS THE OUTER CORE ALSO) IT TAKES A LONG TIME FOR HEAT TO ESCAPE. WHETHER THE TEMPERATURE IS INCREASING OR DECREASING IS A MATTER OF CONJECTURE. SOME OF THE HEAT IS FROM KINETIC ENERGY DUE TO THE AGGREGATION OF THE PROTOPLANETARY DISK, WHICH WOULD IMPLY COOLING. HOWEVER, MUCH OF THE HEAT IS THOUGHT TO BE FROM DECAYING RADIOACTIVE ISOTOPES... WHICH WITH THE ONSET OF CONTINENTAL DRIFT (MANTLE CONVECTION) IN THE PRECAMBRIAN IMPLIES INCREASING HEAT. MANKIND HASN'T BEEN AROUND LONG ENOUGH TO TELL THE DIFFERENCE. 

Q: 2: After any volcano eruptions what happens to the void space from whatever is discharged?
A: USUALLY A CALDERA REMAINS - A LARGE SUNKEN CRATER - OR SOME OTHER COLLAPSE FEATURE APPEARS. OVERLYING LITHOSTATIC PRESSURE GUARANTEES THAT NO VOIDS REMAIN INSIDE THE EARTH - THERE IS NO VOID SPACE ANYWHERE IN THE EARTH EXCEPT FOR VERY SHALLOW CAVES CAUSED BY LIMESTONE DISSOLUTION (KARSTS). 

Q: 3: Could it be possible that earth is a dying sun meaning that the earth for billions of years ago was a burning planet from big bang? Just like the sun as we know it today.
A: THE SUN AND EARTH DID NOT BEGIN TO FORM UNTIL ABOUT 9 THOUSAND MILLION YEARS *AFTER* THE BIG BANG, SO THE EARTH IS NOT HOT FROM THE BIG BANG (AT LEAST NOT DIRECTLY). AS AN ASIDE, EARTH IS NOT A SUN.

NOTE: a thousand million = billion in America. A million million = a billion in the UK.

THE SUN IS USING UP ITS HYDROGEN FUEL AT A RATE THAT WILL LEAD TO A NOVA IN ABOUT 5 THOUSAND MILLION MORE YEARS. THERE IS SOME EVIDENCE THAT THE EARTH WENT THROUGH A FROZEN "SNOWBALL" STAGE IN THE ARCHEAN EPOCH (MORE THAN ~2,500,000,000 YEARS AGO), BUT THIS IS POORLY UNDERSTOOD (THE EVIDENCE IS TRULY ANCIENT). THERE IS EVIDENCE (STROMATOLITE FOSSILS) THAT THE EARTH RESIDED IN A TEMPERATE ZONE LIKE TODAY AS FAR BACK AS ~3,400,000,000+ YEARS AGO.

Q: Climate change:
Don’t believe its cause by man; for sure man is the cause of poor air quality.
A: IF YOU DON'T ACCEPT THE VAST AND GROWING EVIDENCE FOR CLIMATE CHANGE, THEN YOU ARE PART OF A VERY SMALL MINORITY AMONG EDUCATED PEOPLE. 

MORE THAN 98% OF SCIENTISTS WHO STUDY CLIMATE CHANGE AGREE THAT THE EVIDENCE STRONGLY INDICATES THAT MAN IS THE CAUSE OF CLIMATE CHANGE. THE RAPIDLY GROWING CO2 IN THE ATMOSPHERE, A WELL-MEASURED GREENHOUSE GAS, HAS AN ISOTOPIC SIGNATURE LOW IN CARBON-14: THIS MEANS MOST IF NOT ALL OF THE NEW CO2 WAS SEQUESTERED FOR A MINIMUM OF 50,000 YEARS AS BURIED HYDROCARBONS, AND MORE LIKE HUNDREDS OF MILLIONS OF YEARS. IT IS RELATIVELY EASY TO CALCULATE THE AMOUNT OF FOSSIL FUEL BURNED IN THE PAST CENTURY, AND TIE IT TO THE INCREASE IN CO2. HOWEVER, THE HUNGER FOR MEAT PROTEIN HAS ALSO MEANT AN EXPLOSION OF DOMESTIC RUMINANTS (SUCH AS COWS) THAT EMIT VAST AMOUNTS OF METHANE, A GREENHOUSE GAS UP TO 37 TIMES MORE POTENT THAN CO2. ONE COW EMITS AS MUCH METHANE IN ONE DAY AS THE VOLUME OF THREE OF MY FILING CABINETS. MULTIPLY THAT BY 37 TO GET THE EQUIVALENT CO2 RELEASE. THE GEOLOGIC RECORD SHOWS THAT THERE HAVE BEEN CLIMATE CHANGE EPISODES IN THE PAST, BUT NONE THAT HAPPENED ANYWHERE NEARLY AS FAST AS IT IS HAPPENING RIGHT NOW - IT TOOK HUNDREDS OF THOUSANDS OF YEARS INSTEAD OF OUR CURRENT HYPER-SPEED, CHANGE-IN-A-CENTURY RATE). 

I CONCUR WITH YOU THAT MAN IS DEFINITELY THE CAUSE OF POOR AIR QUALITY. 

Q: How about magnetic poles so when the suns positive pole is close to earths negative it will bring the 2 closer and opposite when negative is close to negative also the moon must have effect there.
A: YOU ARE THINKING OF HOW BAR MAGNETS BEHAVE CLOSE TO EACH OTHER - THIS IS A FAULTY ANALOGY BECAUSE OF FACTORS OF BOTH SCALE, PROCESS, AND DISTANCE. THE SUN IS 144,000,000 KILOMETERS FROM THE EARTH. THE SOLAR WIND *DOES* INTERACT WITH THE MAGNETIC POLE OF THE EARTH (AURORAS). THE STRENGTH OF THE SOLAR MAGNETIC DIPOLE IS FAR TOO SMALL TO INFLUENCE THE EARTH'S MAGNETIC DIPOLE, WHICH IS APPARENTLY DRIVEN BY THERMAL CONVECTION IN THE CORE OF THE EARTH. 

Q: PS: Science is like religion you either believe in it or not, however science has a few fact but if they come off wrong at the start everything is wrong
A: I PARTIALLY AGREE WITH YOUR PS: *SOME* PEOPLE ATTEMPT TO MAKE SCIENCE THEIR RELIGION. I DON'T THINK THAT IS WISE, BUT I UNDERSTAND HOW IT CAN HAPPEN. I AGREE THAT FAULTY SCIENCE CAN LEAD TO FURTHER MISTAKES, LIKE HOW SOVIET GENETICS WAS CRIPPLED FOR DECADES BY THE SO-CALLED STALINIST GENETICIST LYSENKO. HOWEVER, WHILE SCIENCE IS THEORETICALLY A SELF-CORRECTING PROCESS, IT IS NEVERTHELESS IMPERFECT, A VERY HUMAN PROCESS. IT SHOULD THEREFOR NOT BE WORSHIPED. 

IF YOU DON'T BELIEVE IN SCIENCE THAT IS FINE, BUT IT MARKS YOU AS SOMEONE WHO HAS NOT STUDIED AND LEARNED ENOUGH TO UNDERSTAND IT. YOU CAN ALSO CHOOSE TO NOT BELIEVE IN GRAVITY, HOWEVER IF YOU THEN STEP OFF THE TOP OF A BUILDING YOUR BELIEF WILL NOT MAKE IT GO AWAY. 

One final comment. Everyone is entitled to an opinion. However, if you base your life and actions on opinions not backed up by facts, you will not live long nor well. MAKING UP facts doesn't make them facts. You can believe that 1 + 1 = 3 but your orbital mechanics BASED ON THAT MATH will not land a man on the Moon. 




Friday, May 5, 2017

Well, how big WAS it?





It is human nature to want to measure things, or at least calibrate big things against other big things. The big and destructive fairly beg quantifying, in fact, so we have for instance the Saffir-Simpson hurricane wind scale (with a top level of 5 for winds above 156 mph/250 kph). This depends only on wind velocities, and doesn’t take into account rain or storm surges (Allaby, 2008). We also have the Fujita tornado intensity scale (Fujita, 1971), which for winds above 261 mph/420 kph can reach a level of F5. The following question asks about measuring earthquakes and volcanoes, which are much harder to quantify than wind-speed velocities.


Q: Hi I am an 8th grade student and I was wondering what determines the magnitude of an earthquake or what determines the power of a volcano...
- Caleb Le M.


A: Your question has two parts, which I will answer in order:

1. Earthquake magnitudes are calculated many different ways, but ultimately it comes down to measuring the amplitude of the actual ground motion (up-down, side-to-side, front-back) on multiple seismometers, and correcting for the varying seismic velocities and the distance separating these seismometers from the earthquake epicenter. Of course you have to calculate the distance to the epicenter first by triangulation from three or more seismometers (and also correct THOSE results by different velocities of sound in the different rocks between the hypocenter [the actual source] and the different measuring seismometers). 

Asking a seismologist how big an earthquake was is like asking a friend to describe how big someone is? Do you mean tall? Wide? Heavy? Some combination of all of these? Does this dress make me look fat? Seismologists do NOT like being asked how they calculate a magnitude, because it will generally require a 30-minute explanation. Therefore, their first reply is often which magnitude are we talking about here?

The original earthquake magnitude scale (Richter, 1935) was the first coherent attempt to define something that is ultimately very three-dimensional and complex. The original Richter scale  measured only the energy in the low frequency end of the seismic energy spectrum, standardized to the particular type of Wood-Anderson seismometer available at the time. Today a modified Richter magnitude is called the “local magnitude” or ML, and is tuned for the rocks and sediments of a local region. For southern California, the equation to calculate this magnitude (Spence et al., 1989; Bormann and Dewey, 2014) is:
ML = Log (A) + 0.00189*r - 2.09,
…where A = amplitude of maximum ground movement in nanometers measured at the seismometer, r = distance from the seismometer to the epicenter in kilometers, and – 2.09 is a correction factor. This equation works only for southern California, and doesn’t work for Cascadia, Japan, the Mediterranean, or Indonesia, which are each served better by different numerical factors.

Another way to calculate an earthquake local magnitude is to work off of an analog log-scale diagram such as in this link:

Though relatively easy to understand and use, the Richter Scale is no longer commonly used.

There are also Mb (the body-wave magnitude), MS (the surface-wave magnitude), and Mw (the moment magnitude). Most of these track closely together for magnitudes of M = 2 to M = 5, but diverge for larger and smaller earthquakes. In part this is because some wave-types strongly influence a short-period or broadband seismometer (which are sensitive to higher frequencies) while other wave-types (for example, surface waves) more strongly affect a seismometer designed to optimally measure low-frequency energy in the 1 – 2 Hz range.

For large earthquakes, MW (Moment Magnitude) is the preferred magnitude, because it more fully represents everything emanating from the earthquake hypocenter. The “moment” MO is calculated as a product of ยต (the shear strength of the rocks) times S (the surface area of the fault tear), and d (the displacement – how far did one side of the fault move with respect to the other side). The largest ever recorded earthquake was the Great Chilean event of May 1960, which had a moment magnitude Mw = 9.5

Confused yet? There is also Me (the energy magnitude – a measure of the potential damage to man-made structures), and Intensity (the measure of surface-shaking damage observed). They are related. Energy release is generally proportional to the shaking amplitude raised to the 3/2 power, so an increase of 1 magnitude corresponds to a release of energy 31.6 times greater than that released by the next lower earthquake magnitude. In other words,
Magnitude 3 = 2 gigajoules
Magnitude 4 = 63 gigajoules
Magnitude 5 = 2,000 gigajoules
Magnitude 6 = 63,000 gigajoules
Magnitude 7 = 2,000,000 gigajoules

These numbers dwarf the puny power of hydrogen bombs, by the way,  

Both Intensity and Magnitude depend on many local variables, including surface geometry and velocities of various underlying rock and sediment units. For example, the 1985 Mexico City earthquake had a surface-wave magnitude MS of 8.1 However, because of resonant focusing of seismic waves as the partially-dried-up Lake Texcoco basin lapped onto bedrock, some buildings on one side of a city boulevard had ground motions 75 times greater than the other side (Moreno-Murillo, 1985; see also http://earthquake.usgs.gov/learn/topics/measure.php ). A friend (Mauricio de la Fuente, a Mexican geophysicist) who lived through this event told me that it was amazing to stand in that street and see everything on one side standing, and everything on the other side flattened. Over 8,000 people died, many in buildings on that (Texcoco ancient lake) side.

Intensity is based on the Mercalli scale (https://en.wikipedia.org/wiki/Mercalli_intensity_scale). It is a twelve-level scale designed to fit to differences in observed damage. The name Mercalli is attached to a scale that Giuseppe Mercalli revised from an earlier Rossi-Forel scale, and which has been further modified multiple times since then (http://pubs.usgs.gov/gip/earthq4/severitygip.html ). On the Modified Mercalli scale, the 1985 Mexico City event scored an intensity level of IX (“Violent”). There are higher levels (and scarier words) than that, by the way.

One more thing to think about: seismologists estimate that only 1% to 10% of the energy of any given earthquake is released as seismic waves. Almost all the rest of the energy is released as heat (http://earthquake.usgs.gov/learn/topics/measure.php ). This figures indirectly into models designed to emulate the complex breaking process of a fault tear, because at some points, wall-rocks are literally welded together by the intense heat, forcing complex movements around these focal points (Dieterich, 1978; James Dieterich, personal communication 2016).

Moment magnitudes are calculated by complex equations that take into account a number of factors including different velocities and different attenuation of seismic energy in different rocks.

An earthquake on the San Andreas fault system will almost certainly be smaller than an earthquake where I live in the Pacific Northwest. This is because the San Andreas fault plane (at least the earthquake shears visible from the surface) can only go down vertically 10 to 15 kilometers before the crust turns plastic. A subduction earthquake, however (think of the Great Tohoku Earthquake of Japan in 2011) occurs on a SHALLOWLY DIPPING fault plane. The depth-direction part (dipping in the direction of the Japanese Archipelago) of the fault-tear actually extended over 200 kilometers! It has been estimated that the surface rip was at least 200 km x 300 km!  By comparison, a major earthquake on a part of the San Andreas fault system might be "just" 100 km x 15 km. 


2. The "power of a volcano" is generally characterized by scientists as Volcano Explosivity Index or VEI. This is a relative measure of explosiveness of volcanic eruptions, and is open-ended with the largest supervolcano eruptions in pre-history (Yellowstone, Toba, Taupo) given a magnitude of 8 in this classification system. The 79 AD eruption of Vesuvius and the 1980 eruption of Mount St Helens in Washington State are both rated a VEI 5 on this scale. The VEI number attached to a volcanic eruption depends on (a) how much volcanic material (dense rock equivalent) is thrown out, (b) to what height is it thrown, and (c) how long the eruption lasts. There is no equation to calculate this scale (it is like the Mercalli scale based on visual observations), but it is considered logarithmic from VEI 2 upwards. In other words a VEI = 5 event represents approximately 10 times more energy than a VEI = 4 event. Follow this link for more information on how to assess the VEI magnitude (from Newhall and Self, 1982):


References:

Allaby, Michael, 2008, Saffir-Simpson scale, in: A dictionary of earth sciences (3rd ed.): Oxford University Press, 1672 pp. ISBN 978-0-1992-11944

Bormann, Peter; and James W. Dewey, 2014, The new IASPEI standards for determining magnitudes from digital data and their relation to classical magnitudes:
doi: 10.2312/GFZ.NMSOP-2_IS_3.3

Dieterich, James H., 1978, Time-dependent friction and the mechanics of stick-slip: Pure and Applied Geophysics 116, issue 4, p. 790–806. doi: 10.1007/BF00876539

Fujita, Tetsuya Theodore, 1971, Proposed Characterization of Tornadoes and Hurricanes by Area and Intensity: Satellite and Mesometeorology Research Paper 91. Chicago, IL: Department of Geophysical Sciences, University of Chicago.

Moreno-Murillo, Juan Manuel, 1995, The 1985 Mexico Earthquake: Geofisica Colombiana. Universidad Nacional de Colombia 3, p. 5–19. ISSN 0121-2974.

Newhall, Christopher G.; and Self, Stephen, 1982, The Volcanic Explosivity Index (VEI): An Estimate of Explosive Magnitude for Historical Volcanism (PDF): Journal of Geophysical Research 87 (C2), p. 1231–1238. doi: 10.1029/JC087iC02p01231.

Richter, C.F., 1935, An instrumental earthquake magnitude scale (PDF): Bulletin of the Seismological Society of America. Seismological Society of America 25 (1-2), p. 1–32.

Spence, William; Stuart A. Sipkin; and George L. Choy, 1989, Measuring the size of an earthquake, in: Earthquakes and Volcanoes 21, Number 1, 1989.
http://earthquake.usgs.gov/learn/topics/measure.php