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.).

The question was typical. The follow-up question was definitely NOT.

Q: Hey I'm wondering how many earthquakes occur every week ? And how powerful they are......

--Rossy K

A:  The answer to your question depends on how BIG the earthquakes are that you are talking about. The smaller the earthquake, the more common they are. This means that there are probably many undetected (very small) earthquakes happening around the world every second. This also means that the really big ones - the ones that get in the news - are not very common at all.

    The US Geological Survey estimates that several million detectable earthquakes occur in the world each year. Many go undetected because they originate in remote areas or they have very small magnitudes. The National Earthquake Information Center now locates about 50 earthquakes each day, or about 20,000 a year, worldwide. They have to be above a certain minimum threshold before an effort is made to even try to locate them.

    There are far fewer large events than small earthquakes, and this table will show you how these are parsed out according to magnitude:

Frequency of Occurrence of Earthquakes

Magnitude                         Average Annually

8 and higher                            1                                             

7 - 7.9                                    15                                          

6 - 6.9                                    134                                        

5 - 5.9                                    1319                                      

4 - 4.9                                    13,000   (estimated)       

3 - 3.9                                    130,000 (estimated)       

2 - 2.9                                    1,300,000 (estimated)

    I would recommend that you visit this web-page:

    http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

    There are lots of interesting statistics here.

*************

Q: What’s the meaning of life?

--Rossy K

A: Ask your parents, and they will give you a start on answering that question. I just answer questions about geology.

On average you have upwards of 70 more years to figure this out yourself. That's pretty much the whole point of your being on this planet. 

Do Small Earthquakes Prevent Large Earthquakes?

Here's another question about earthquakes. It doesn't really address "slow-slip" earthquakes or induced seismicity, but clearly the questioner has been reading...

Q: Do small earthquakes prevent larger earthquakes from occurring? 
- Laurie F

A: There is an argument to that effect within the earthquake research community. Theoretically, a series of small events might accommodate (re-equilibrate, redistribute) at least some of the strain being built up by tectonic forces. In the practical world this works only imperfectly. For instance, we know: 

2....that waste water injection into oil wells north of Denver, CO, led to a significant cluster of micro-earthquakes. Apparently the fluid lubricated fault surfaces that were collecting strain. There wasn't a lot of energy released by this process, but it caused earthquake scientists to sit up and listen.

2....that there are "slow slip" earthquakes on subduction faults that cannot normally be felt, but are only "seen" by noting slow displacement changes in continually-recording GPS instruments. An example of this has been measured in the Olympic Peninsula of Washington State, and another example has been observed on the south coast of the Big Island of Hawai'i. 

This small-event re-equilibration process works for parts of a subduction fault surface - for instance the shallow and deep parts of the down-going Juan de Fuca oceanic crustal slab currently being subducted beneath the Pacific Northwest Cascades. However, there is a section of this (and other) subduction fault(s) that does NOT release strain in small increments like this. This part remains "locked."

When these locked sections "rip" (fail) there can be many meters of abrupt displacement. THIS process is the source of the greatest earthquakes ever recorded, including the last great Cascadia earthquake of January 1700 AD, which caused an "orphan tsunami" that devastated the Sendai coast of Japan many hours later without any warning.

What kind of house base absorbs the most shock

There are real, practical consequences from geology that affect every single one of us. Here's another, though you have to think like an engineer to understand all the issues involved.

Q: What kind of house base absorbs the most shock during an earthquake? - Maddie D-N

A: There are two different aspects of the same issue here: a "walking" building, vs a shock-absorbing building.

1. A building foundation that is anchored in bedrock will SHIFT the least. The foundations of my house in Washington State are built (excavated) down into bedrock. In addition, all parts of the foundation are tied together with reinforced concrete. This will keep my house from "doing the splits" when the next Cascadia earthquake hits. Being anchored in bedrock means I have a better chance that my house won't take a ride - walk - over to my neighbor's property, either.  During the Loma Prieta earthquake of 1989 in northern California, some houses that "walked" and some that "did the splits." They were build on landfill in North Beach, landfill made up largely of debris from the 1906 Earthquake dumped there nearly a century earlier. Their foundations failed - sagged, did the splits - because they were not tied together, nor were they anchored in bedrock. That landfill turned partially liquid with the shock waves passing through it. In geology-ese, this is "liquifaction."

2. There are some (generally rare) structures designed with shock-absorbing materials between the bedrock-grounded base and the structure itself. Some examples include the Trans-Alaska pipeline, and the underground facilities hosting NORAD (North American Air Defense Command) in Colorado Springs, CO. Designing a structure to ABSORB the most shock is a very expensive thing to do, however, and when NORAD was built during the early Cold War, cost was not an issue. 

   However, no matter what the structure is, engineers must decide on how BIG an event to design for.(i.e., how much displacement can they anticipate). There is not enough money to design everything in the country to survive a magnitude 8 or 9 earthquake, as we sadly learned with the Great Tohoku earthquake of 2011. The Fukushima Dai-Ichi nuclear plant had been built to survive a Magnitude 7+ event. It was unable to withstand the consequences of a magnitude 9 event (the initial shaking and the 15-meter tsunami that followed). To build it for this, the facility would have cost one or two orders of magnitude more than it did, and no one had ever experienced a M = 9 event in Japan before. 

People around the Pacific Rim will live for many years with the consequences of that structural inadequacy. 

~~~~~

Landscape Change - The Consequences

Landscapes change – sometimes gradually, but also sometimes in fits and spurts. There are real-life consequences to this change.

Q: When the area drifting from Africa eventually fully separates will any animals become extinct? How many new animals would be expected to evolve? How long would it take for the scenery to greatly differ from how it once was?

- Veronica V

A: Your question is ambiguous, so I will take it upon myself to infer that you mean the ~6,000-kilometer-long Great Rift Valley of Africa.

That name itself is somewhat ambiguous, since it combines features from a number of separate although related rift and fault systems stretching from Jordan to Mozambique. This continental split has been forming since at least the Miocene, 22–25 million years ago, and is currently pulling apart at a rate of about 7 mm per year. At that rate of extension, a complete rupture will occur within 10 million years, and the Somalian plate will break off, forming a new sea between it and Africa not unlike the Red Sea.

As to the animals, well, if history is any predictor of the future you can expect several things:

1. VAST numbers of animal species will go extinct this century. This is due to habitat elimination, over-hunting, and climate change. You are watching this “Sixth Extinction” happen right now, as poachers decimate African Rhinos and Elephants for their horns and tusks, and Tigers in Asia for their internal organs and bones, just to satiate a bottomless appetite in Yemen and China.

2. Those that survive on the “New Madagascar” that will be the eventual Somali Island will evolve to fit their altered ecosystem. Often this means they will grow smaller – evolve to better use the limited resources of a now-limited landscape.  

Landscape Change - How Fast?

A major question from the beginning of geology as a science has been how fast does change take place? From the Literalist read of the Bible, it would seem 6,000 years is far too short a time to permit the development of tens of thousands of meters of sediment, with remains of primitive life-forms at the bottom and advanced life-forms preserved at the top. The first rough estimates of the rate of sedimentation were made in England, by thoughtful natural scientists measuring how fast mud accumulated in a pond. These early geologists had already mapped thick stacks – thousands of meters of distinctive layers - of sediment in cliffs, road-cuts, and quarries. They had seen the same sequences long distances away, implying the same sedimentary process was happening over a very wide area. Finally, they had realized that for mud and sand to accumulate to thousands of meters of thickness, would take at minimum many millions of years. This was really the first baby step of geoscience.

Q: Hello, my name is Jurgen and I am currently enrolled in an AP Environmental Science class and have a question about river formation. I hope you can answer my question.

How long does it take for a gully or rill to be formed into a river if there is a constant stream or supply of water running through the land?  Thank you.

--Jurgen P

A: Time for a gully to become a river can vary wildly from less than a hundred to many millions of years. Generally, most terrains are in some sort of equilibrium and don't change much over time – unless disturbed by something, like a tectonic event. This is sometimes called "punctuated equilibrium." The change of a feature from one form to another (like a gully to a river) implies a permanent shift in the rainfall regime - some form of climate change – or tectonic uplift.

Change from a gully to a river could also have a lot to do with human intervention. I've walked down 10-meter-deep, steep-walled gullies that were really mini-canyons (Arroyos) in SE Arizona. These apparently didn't begin to form until man introduced cattle in the late 19th Century. Early journals from some of the first visitors describe “grass that was belly-high to a horse.” These cattle quickly wiped out the native prairie grasses by over-grazing the landscape. When Arizona earned its statehood in 1912, it had a human population of about 12,000 people, but an estimated cattle population of perhaps 10,000,000. Soils started disappearing rapidly with no roots to hold them, and small rivulets began to rip through the landscape and form small canyons in less than a century. Events like this, and the 1930's Dust Bowl, lead to the formation of the US Bureau of Land Management and the US Soil Conservation Service during the 20th Century.

Tectonic uplift can also weigh in powerfully, but tectonic shifts are generally relatively slow - slow at least in typical human time-frames. The Grand Canyon only began to form (cut down through pre-existing Precambrian to Mesozoic rocks) about 70 million years ago. The actual timing of the initial incision and the final down-cutting is still being argued today by geologists as more evidence accumulates, but it appears to have been quite rapid at the beginning.

Unconformity? Disconformity?

Here's a purely geologic question by someone who has already taken at least one course in geology. The question opens up and highlignts the three-dimensional aspect of geology - and why mathematics (especially geometry) is such a fundamental prerequisite for studying geology. Some people persist in saying that a geologist is just someone who didn't do well in physics or math. The hard reality is that physics, math, chemistry, and English composition are the building blocks - the basic tools - of a modern geologist. Some of the most sophisticated geology being carried out these days is done with computers. Drill-hole information is fundamentally three-dimensional, and the ability to construct three dimensional landscapes from surface mapping and drill-hole intercepts is just so very cool. To rotate this 3D landscape on one or several computer screens, showing how individual components evolved in time in a single giant cubic space... is absolutely essential to numerically assessing any resources the land under the geologic map may host.

Q: I have a question regarding identifying unconformity on geological map. I have attached a map as an example. How do we identify unconformity on such 2D geological maps if each colour represents a different rock? Please advice.

Thank you and hope to hear from you soon. Regards

- Hazel A

A: I have not downloaded your map and looked at it in detail, but just looked at it via the attached thumbnail. We are discouraged pretty strongly from downloading and opening any files from unknown individuals that might potentially be vectors for malware. For the purposes of this Q/A, a map is not really necessary, however. 

I'd like, instead, to address your question on a somewhat broader level: The inherent problem with a geological map is that it represents the surface of the land. It's a view looking downwards from space, which is not always the same as looking downwards in time. Sometimes, with tectonic and erosional events, older in time doesn't necessarily mean deeper in the Earth.

An unconformity is a gap in sedimentary deposition for one of several fairly specific reasons: non-deposition, subsequent erosion, etc. It is not easily represented in a geologic map, which only shows just one sub-horizontal surface - the part exposed to the sky. An unconformity means that there has been a time break in the geologic record. This is quite different from a juxtaposition of different geologic units due to, say, a thrust fault (though they could both be involved at the same time). 

In practicality, this means that the geologist who produces the map must somehow indicate or convey any unconformity (or disconformity, or nonconformity, or paraconformity, etc.: see http://en.wikipedia.org/wiki/Unconformity ) in her/his *Correlation of Map Units* columns on the side of the geologic map.

For most people not intimately familiar with a particular local or regional geology, it would be very difficult if not impossible to determine if some break between units is an unconformity or a fault juxtaposition just from looking at a geologic map alone. A change in rock-type could mean any of several much more common things: a change in sedimentary regime (like an ocean transgression), an intrusive event (like a big granite body punching up from the Mantle), a volcanic eruption, any of several different kinds of fault, etc., exposed at the earth's surface. 

It comes down to the fundamental difference between a map view (looking down at the ground from space),  and a cross-section view (looking at the ground side-ways, as if a giant trench had been cut in the landscape). However, even in an exposed cross-section, considerable sleuthing is required to determine if a break is an unconformity or not.