Volcanoes Part 1: Welcome to Japan!

With several recent eruptions making the news, I'd like to do a series about volcanoes. Japan is an interesting place to start, not only because I have some nice pictures from there, but also because it is home to over 100 active volcanoes, 10% of the world's total. In fact, the islands of Japan were formed by volcanoes, similarly to those in Hawaii. The picture above shows the city of Kagoshima with the active volcano Sakurajima looming in the background, but more on that volcano later.

First, let's discuss what is meant by an "active" volcano. The term is a bit misleading in that it sounds like the volcano is currently spewing ash and lava or is otherwise showing activity in some way. While currently erupting volcanoes, such as Sakurajima, are certainly classed as active, any volcano that has been active within recorded history (or sometimes longer) can be considered "active". A volcano that was only active earlier than that but is expected to be active again is called dormant, while a volcano that's not expected to erupt again is called extinct. Unfortunately, the definition details of these terms vary depending on who you ask, but the general idea holds for all.

So, why does Japan have so many active volcanoes? Well, it's in an ideal location for volcano formation (and also earthquakes) - right above a subduction zone (or rather a few). Recall that plate tectonics describes how the Earth's crust, the thin, top layer of hard rock, is broken into pieces (plates) that drift around on the more fluid-like (but still solid!) parts of the inner Earth. A subduction zone is an area where one of these tectonic plates is being pulled or pushed into the Earth beneath another plate that is more buoyant. Think of two pieces of ice floating on a lake. If one is more dense, it won't float as easily allowing the lighter ice piece to move over it.

Since plates made of oceanic crust are denser than those with continental crust, they are the ones that subduct. The oceanic plates pull some water along down into the Earth, either within the rocks themselves or in the upper sediment layers. As the plate gets deeper, the temperature and pressure increase and the water is released into the surrounding "rock". Water lows the melting temperature of rock, allowing some of it to melt and become less dense. Buoyancy causes it rise to shallower parts of the Earth where it pools and can eventually erupt.

Over time, the eruptions deposit more and more material on top of the crust, building up a volcano. If the subduction zone is below water, the volcano won't be seen until it grows large enough to appear above the water. Therefore, ocean island volcanoes are much larger than they seem since most of their bulk is hidden from the surface. Because this process happens along the subduction zone, not just at one location, you can end up with a volcanic arc, like Japan. Some volcanoes are also close enough that they eventually begin to grow on top of one another. The result is larger islands made of multiple volcanoes - also seen in the main islands of Japan.

Recently, you may have seen the news of the new island that formed off the coast of Japan. This is a great example of these processes in action. Of course, this isn't the only way to form volcanoes or volcanic arcs. We'll get to the others in later parts of this series.

If you're interested in current volcano eruptions and warnings in Japan, you can check the Japan Meteorological Agency website.




References

VHP Photo Glossary: Volcano by USGS (United States Geological Survey)
Subduction Zone Volcanism by San Diego State University
Dramatic Video Shows Volcano Making New Island Off Japan by Brian Clark Howard
Volcanic Island Eats Another by Brad Lendon
Resources from Volcano Discovery:
Volcanoes of Japan (118 volcanoes)
What's erupting? List & map of currently active volcanoes

Why "God" Is a Poor Explanation

I may be coming back to the blog with a seemingly controversial topic, but it's been on my mind lately and this specific topic isn't quite as controversial as it might at first seem. I'd like to preface this post by saying that I have few quibbles with religion. In fact, this post is not about religion but rather about inquiry and the lazy thinking that is sometimes derived from religion (but not always! - You could easily replace "God" with "Because that's how it is".).

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Science and religion are not opposed to each other, as many people would like you to believe. They are sold as enemies because today's society likes drama and conflict provides bucket-fulls of it. But, it wasn't always that way. Even though there are fewer religious scientists nowadays (and I know some of them), centuries ago most people, including most scientists, were religious. Go far enough back and you'll find no scientists but rather natural philosophers. The influence of this is still felt today in the Doctor of Philosophy (PhD) degree that is the highest level degree awarded to both scientists and non-scientists.

"Philosophers", in the vaguest sense, are people whose curiosity gets the best of them. Their inquiry and questioning of any and all aspects of the world are what drives innovation and increases knowledge. The only limits that philosophers have are their abilities to logically argue for an explanation, generally relying on any of the various types of evidence and reasoning.

Scientific explanations go one step further - they must make testable predictions. For example, take Einstein's Theory of General Relativity. This theory essentially made Newton's Theory of Gravity more widely applicable. It added more detail and gave more precise results. Not only could General Relativity explain observations that Newtonian Gravity could not (e.g. no instantaneous influences), it also made predictions (e.g. the sun bends light from distant stars) that were later observed and confirmed to be true. This requirement ensures that scientific explanations can always be confirmed or re-evaluated and either tossed out or revised. The end result is explanations that are always improving.

Now, this brings us back to the initial point of the post: why "God" is a poor explanation. The problem with using "God" as an explanation for things is that it removes all of the things previously mentioned -  inquiry and curiosity, reasoning and evidence. Even religious philosophers, like those who study the holy books, use these 4 main ingredients, if you will, of good argument. Let's consider what happens when the most important of those elements, inquiry, is removed.

Isaac Newton was a religious man, like most people of his time. That, however, never stopped him from asking questions (inquiry) and finding answers, not only about the physical world but also about the spiritual/religious one.

Everyone knows the story of Newton and the apple tree. Upon sitting under one on a sunny day, an apple fell from the tree and hit his head. This is what led him to his theory of gravity. But, what if instead of thinking more deeply about why apples fall from trees, he simply answered "because God makes them fall"? For him, this could have been a perfectly acceptable answer, but it wasn't satisfactory and doesn't require any further thought. If he had stuck with that answer, there might not be a theory of gravity, or at least, the theory would have come later by someone else.

So why does that matter? Apples will fall regardless of whether or not we have an explanation for why they do so. Remember before when I said that General Relativity expanded on Newtonian Gravity? If everyone used the "God" explanation, then there would be no theory of gravity or General Relativity. This also might not seem like a big deal, until you realize that one big application of General Relativity is GPS. Without knowledge of the effects described by General Relativity, GPS would likely be much, much less effective, if it even existed at all.

This game can be played with most "explanations" of our world, from physics to marketing. We have current society because there were philosophers who weren't afraid to follow their curiosity and ask questions, regardless of their religious ideology. Does that mean that "God" can never be an answer? Absolutely not. Sometimes, we just don't know enough to come to a satisfactory explanation. At this point, perhaps we can say "because God" - at least until someone smarter comes along. And, perhaps, there are some questions that will always remain in the "hands of God".


References and Further Reading (For inquiry!)
General Relativity by Harrison Prosper
Relativity and the Cosmos by Alan Lightman
Isaac Newton's Life by Isaac Newton Institute for Mathematical Sciences
Einstein's Relativity and Everyday Life by Clifford M. Will

Update

 
I apologize for not writing much lately. I've spent the past 2 weeks traveling to/from and attending a volcano conference and acoustics workshop. I have some great pictures with some great science, so hopefully I'll be able to find the time to start posting more regularly again. Thanks for reading!

How Do Animals Dry Themselves by Shaking?

** Apologies on not posting for a while. I hadn't noticed how long it's been! **

This is not a photo (!) but a video that I came across a couple years ago. The authors from Georgia Institute of Technology applied some basic physics to determine how quickly an animal has to shake in order to dry itself. Here's their website where you can find a more detailed description of their study, including the resulting published paper. Being a fan of applied physics, I really enjoyed this, especially because it is simple enough for an introductory physics student to understand.

The basic idea is to look at the forces acting on the water droplets in an animal's fur. The force exerted by air pressure and water tension work to hold the droplets in the fur. By shaking, the animal produces a force that acts to move the water droplets outward. This is called the centripetal force. When you are next in a car, notice how you move when the car makes a turn, especially if it's a quick turn. You should feel your body moving away from the pivot point. In other words, a right turn will cause you to move toward the left side of the car. This is also the centripetal force at work, and it occurs whenever a body is rotating.

The centripetal force produced is proportional to the angular frequency, or speed, of the rotation as well as the distance from the pivot point to the object that is rotating. For our rotating mammals, the pivot point is the center of the body and the object, the water/fur. Therefore, the distance is just the radius (or half the thickness) of the mammal's body. The conclusion that smaller animals must shake faster makes sense because of this proportionality.

Let's introduce the actual equation for rotational motion and centripetal force: Fc = m*r*w^2, where Fc is the force, m is the mass of the water droplet, r is the radius of the animal, and w is the angular frequency with which it shakes. Assume we want to keep Fc constant - that water droplets always require the same amount of force to remove them. Since a smaller animal has a smaller radius r, it will require a larger rotating speed w to compensate for the smaller r. Larger animals with larger radii, can shake more slowly to produce the same centripetal force as their smaller companions.

Here's a challenge: Next time you're at the beach or get out of the shower, try to shake yourself dry. Can you do it? If so, what do you think your shaking speed (oscillations per second) is? If not, what makes you different from the mammals that do dry by shaking?

References

Wet mammals shake at tuned frequencies to dry by Andrew Dickerson, Georgia Tech

Why Does the Moon Have Phases?

** My apologies on the lateness - it's been a busy month. **

 

Full moon. Crescent moon. New moon. There's no doubt you've previously heard these or even talked about them. Perhaps you even know the less common or more specific phases of the moon. Yet, there still seem to be misconceptions about the moon's appearance. I've already covered why the full moon can seem so large and why the moon can appear orange when it's on the horizon. Here's some more information about the moon's appearance:

The Moon's Orbit & Apparent Size

Let's start with some important background knowledge. The moon orbits the Earth on a nearly, but not perfectly, circular path. As a consequence, there are two points where the moon will be at its closest (perigee) and farthest (apogee) distance from the Earth with every other point somewhere in between. The difference in distance between the two extremes is enough to be noticeable, at least with pictures. It might be a bit difficult to see the difference by just going outside and taking a look. Another neat thing about the moon is that it's tidally locked in its orbit. For every one orbit around the Earth, it will rotate exactly one time. The result is that someone on the Earth can only ever see one side of the moon. If you compare the two pictures above, you'll notice that the dark lunar mare near the bottom right corner of the crescent moon is the same as that on the right side of the gibbous moon. On the flip side, there is one side of the moon that we can never see from the Earth. This is where the "dark side" of the moon comes from. The dark side of the moon isn't dark in the true sense of the word. There are times when the sun shines on it. However, it's considered "dark" because people were never able to see it until lunar orbiter spacecraft were built and sent into space.

Moon Phases

Unlike the sun, the moon does not emit light on its own - we only see it because of the sunlight that it reflects. Like the Earth, the moon will only have sunlight illuminating half of it at a time. The half that is illuminated is not always that half of the moon that faces the Earth, which leads to the phases. I'll be a bit more specific with a few examples to help clear up any confusion. When the moon is full, the half that is illuminated is also the half that faces the Earth. The moon is on the opposite side of the Earth than the sun, so the sunlight illuminates the half that faces us. The opposite of this is the new moon. In this case, the moon and sun are on the same side of the Earth, so the half that is illuminated is the "dark" side of the moon. 

This case also brings up another interesting point: the new moon should be located close to the sun in the sky. In other words, we see the new moon during the day rather than at night. It doesn't disappear from the sky or become dark. Instead, it is just visible at a different time of day. 

Let's leave this little detour and get back to the phases. The last example that I'll give is the half moon. To see a half moon in the sky, the moon would be 90 degrees from the sun. If you have trouble visualizing that, picture it this way: if the Earth is a clock, the sun will appear near the 12 and the moon will appear near the 3. For this phase, half of the "dark" side is illuminated and half of the side that we see is illuminated. To get the rest of the phases, we can just rotate the moon around the Earth. The farther it gets from the sun, the closer it will get to a full moon. As it moves from full to new, a smaller and smaller section (visible to us) will be illuminated. If you need some extra visualization, you check out this chart or try the activity listed below.

Eclipses

I'm sure most people are well aware of solar eclipses, but did you know that the moon can be eclipsed, too? A lunar eclipse happens when all of the moon, Earth, and sun are aligned with the Earth in between the other two. As the moon passes behind the Earth, it moves into the Earth's shadow. Since the moon appears lit due to reflected sunlight, being in a shadow will make the moon appear darker. At the start of the lunar eclipse, a growing fraction of the moon will appear blacked out. As more and more of the moon moves into the Earth's shadow, it starts to turn a dark orange color. The next total lunar eclipse visible for the Americas will be on October 8, 2014, so get your binoculars ready.

Try It at Home

You can see for yourself how this process works with just a (solid) ball and a flashlight. Begin by placing the ball on a table with the flashlight pointed at it from a couple or so feet away. Walk around the table with the surface at eye level and watch the appearance of the ball. When you're opposite the flashlight (sun), the ball (moon) appears as a dark, "new moon" phase. Go around to the same side as the flashlight, and you'll see a full moon (or rather full ball?). As you walk around, you'll see the phases of the ball changing just like the moon. However, the moon orbits the Earth, not the other way around. For a more realistic demo, place a larger ball (or globe if you have one on hand) a few feet from the flashlight. You can simulate the moon and its phases by moving the small ball around the large one. Place a "person" on the large ball. How does the small ball's phase change from your person's point of view as it moves around in its orbit?

Keep in mind that the moon's orbit is slightly tilted. This means that the moon and Earth rarely appear directly between the sun and the other. By aligning all three, you are creating a solar (moon in middle) or lunar (Earth in middle) eclipse.

References & Further Reading

Lunar Eclipse Page - by NASA

Volcanism on the Moon - by Robert Wickman

The Lunar Orbiter Program - by Lunar and Planetary Institute (NASA)

Earth's Moon Phases, Monthly Lunar Cycles (Infographic) by Karl Tate

Water Waves

Chances are you've been to a beach before, and it's quite likely that there were waves whether you were at the ocean, a lake, or some other sizeable body of water. If you've ever watched the waves for a while, you might have noticed that they tend to arrive parallel, or nearly so, to the shoreline. Even if they are at angle when they are far away, they still reach the shoreline nearly parallel. Why? Another thing noticeable to anyone who has watches waves, and is visible in the above photo, is the crashing and "breaking" of waves as them come towards the shoreline. How does that happen?

The first question can be answered by fluid dynamics. In shallow water, that is at a depth which is smaller than the wavelength (measure of distance between wave crests), the speed of the waves depends on the water depth and gravity only. Specifically, the speed is equal to the square root of gravity times depth. This tells us that waves will move slowest in the shallowest water. Let's assume that there is a nice downward slope as you move away from the shoreline. Start by imagining a wave that begins parallel to the shore. As it moves closer, the shallower water will cause it to slow down. Now, what happens if the wave is rotated so that it starts at an angle to the shoreline?

If you think of the wave crest as a straight line, one end will be closer to shore than the other if it's at an angle. The far end is in deeper water and will travel faster than the shallow end. This causes the wave crest to turn until both ends are at the same depth or it hits the shore (whichever comes first). If you're having trouble imagining this scenario, try thinking about an axle with a wheel on each end. If you move both wheels at the same speed, the axle will move in a straight line. What happens if you hold one wheel stationary (more or less) and move the other? The moving wheel will rotate around the other one. Now, allow both wheels to turn but move one a little faster than the other. The axle will move forward while also gradually turning. This is analogous to our wave scenario.

That's one question answered, so on to the next one: what causes waves topple over? It may seem strange but this answer relies on the same principle as the first one. In this case, we can no longer treat the wave crest as just a line; it does have a finite width, after all. Since the back of the wave is in deeper water than the front, the back will travel faster and eventually catch the front. The water particles will accumulate behind the crest until it reaches a point when the added water forces the wave to topple over. If the wave is large enough, you may notice how the top rolls over the bottom. As water piles up behind the wave, the water becomes even deeper than the water in front. Consequently, the water in back moves even faster, particularly that on the surface. This helps the top of the wave crest to roll as the wave topples over. Keep in mind, however, that this is only valid for waves in shallow water. It's not often that you see breaking waves in the middle of a lake, partly for this reason. When you do see them, the wind is generally very strong and helps force them to topple over.

Fortunately, these are easy things to go see for yourself, so get out and enjoy the coming summer. Maybe the next time you find yourself at a beach, you'll pay a little more attention to the waves.


References
Waves in Fluids (video) by National Committee for Fluid Mechanics Films (1960s; more here)