How Many Earthquakes in a Week- and the Meaning of Life

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.

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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. 

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 flow from Kilauea volcano, and accidentally stepped directly on the magma several times. It damaged my boots. 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.
- 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. 

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

More About Volcanoes

Here are some more questions from the precocious Cadee, this time about volcanoes.

Q: I am in 6th grade, and we are learning about volcanoes. I've been assigned to ask you some questions about volcanoes. 

Question: How many estimated volcanoes are in the world?

- Cadee C

A: ​The Smithsonian Institution Global Volcanism Program maintains a database that currently contains 1,562 volcanoes with eruptions during the Holocene period (approximately the last 10,000 years) or which are currently exhibiting any kind of unrest. There are many, MANY more volcanoes on the planet than that - they are just older. I have mapped volcanoes in Mexico that are at least 100 million years old, and I have mapped volcanoes in Venezuela that are at least 3 BILLION years old. In my office I have a piece of Mount St Helens volcano that was semi-liquid and oozing as red-hot magma just 9 years ago.

Making matters even more complicated is the question of what IS a volcano? When I served a 5-year assignment as the chief scientist for volcano hazards of the US Geological Survey, I asked one of my senior scientists to do a compilation of the Pacific Cascades. I thought he would come up with a list of 15 - 20 volcanoes - the recognizable peaks like Mt. Hood and Mt. Rainier. His final list had over 3,500 entries - he counted every small separate cinder cone and dike.

Q: Are there warnings before a volcano erupts?

​A: Yes, in almost all cases if there are an adequate number of telemetered instruments nearby. Generally we first see the mountain swelling as magma starts to come up into the edifice from below. We "see" this generally with telemetered GPS networks or with satellite radar data (InSAR). Later, as the eruption gets closer in time, we start detecting magmatic gases like H2S (smells like burnt matches), and we begin to detect small earthquakes whose signatures tells us that rocks are being broken below the volcano.​

​You can't predict an earthquake, but you CAN predict a volcanic eruption if you have enough instrumentation in place on or near it.​

Q: Where do volcanoes usually form?

A: ​The vast majority of volcanoes can be found near and along tectonic plate margins - like the so-called Ring of Fire around the Pacific Basin. Some are harder to explain, except as hot spots that tectonic plates are drifting over, such as the Hawai'i chain. ​Some countries exist on Island Arcs - the entire land is made up of active volcanoes, like Iceland and Indonesia.

Q: How do some volcanoes change over time?

​A: If magma moves up into a reservoir well below the ground and stays there for a long while, it can differentiate. By this I mean that crystals start to form, and the heavier ones drift to the bottom of the magma chamber. When the volcano erupts, the less dense material (the lighter-colored stuff with higher silica content, such as rhyolite) tends to come out first, from the top of the reservoir. Later the material from lower down in the stratified reservoir comes out - this tends to be darker and flows more easily (basalt). ​This ends up on top of the lighter, more silica-rich flows. 

This sort of process works until the percentage of crystals rises to the point of the magma becoming a crystal "mush". Then this sort of "flow easily stuff" does NOT flow more easily.

​Some volcanoes change over time because they get different magma feeds from the mantle as continents move to different places on the mantle with plate tectonics. An example like this would be some volcanoes in the western United States that rather dramatically change in character over long periods of time. ​

Q: Are there patterns in volcanic eruptions from the same volcano?

​A: Yes, and we count on these patterns to roughly predict the future behavior of a volcano. This pattern recognition requires very careful geologic mapping and age-dating of the rocks, as you might imagine, to see what was erupted and when ​- and how. This is a rough art still, and volcanologists are always getting surprises - like when Four Peaks Volcano erupted in the Alaska Peninsula a few years ago.  ​No one had any idea that this volcano had ever erupted at all within the previous 10,000 years. ​We had no instruments close to it, so we had very little warning.

Do You Like Your Job?

I'm always impressed when young people are already thinking early about a career - instead of growing older and stumbling along through life, wondering how they got where they are. 

Q: I am in 6th grade, and have been given an assignment to ask you some questions.
Question: do you like your job?
- Cadee C

A: I absolutely love my job. All of it except the bureaucratic stuff.

Q: What inspired you to study geology? 

A: 
- I could be a real world detective. 
- I could pick up a rock and examine it closely, and  understand its history from the clues you or I can see in it.
- I could work on something that actually helped other human beings live better, live happier. Do you go to school in a bus or a car? Do you read using electric lights? Thank a geologist.

Q: what is your favorite area of study? 

A: All areas. I am interested in the full range of geology, and have published scientific papers in such diverse fields as archeology, astrophysics, and groundwater hydrology. the world is just so full of fascinating things, and I want to study all of them.  

Q: what is something fascinating you've learned since becoming a geologist?

A: 
- How a rock the size of my office, traveling at 10 kilometers per second, can carry so much kinetic energy that it can  leave destruction equivalent to an atomic bomb.
- How water moves slowly underground, and how pollutants from a leaky tank at a service station can move with it and poison whole cities.
- How gold gets concentrated by natural processes - and how to find it!
- How an ocean floor can become volcanic lava. 

Q: how has the way you study geology changed over time?

- We use computers very heavily now. We use very sophisticated numerical modeling to understand what is happening under the ground, when we cannot see or detect features otherwise. 
- We spend much more of our time doing bureaucratic things that don't have anything to do with our work. These are increasingly required by Congress because some people there don't trust federal employees to work honestly.  
- We have to work harder and smarter to get the same kind of productivity.