Thurs-Demo: The one that goes boom

It's Thursday. That means another demo. This week, I've been stricken with one of the various plagues that burns through college campuses at the start of the semester. All these viruses with thousands of brand new vectors. It's like some kind of frickin' holiday for them, or something. But since I was producing almost as much mucous as a netted hagfish, I didn't create a new demo this week. But, I have put together a little more information behind a demo I did last fall.



This demo came from an article and web page done by one of my former professors. Their write-up is well detailed and documented, so I'm not going to add much to what's in the journal article. If you really want to do this demo yourself, read what I have to say about my experience and then go read what Harpp et alia have to say. Pay special attention to the safety info. If you've never handled liquid nitrogen (LN2), you really want to pay attention. The stuff can be fun to experiment with, but only if handled safely.

I have embedded the video mashups from our demo runs below. Some things to look for include:

• Our first attempt exploded almost immediately. To make the bottle sink to the bottom, we poured it about 2/3 full of sand. This reduced the available gas volume and forced the bottle to burst too quickly.



• One attempt just sank to the bottom and then bubbled out. This was because I placed a "tall" cap on a "short-stem" bottle. Pay attention to this - some bottles have a shorter threaded neck and the taller caps won't seal properly.
  



• If you experiment with larger or smaller bottles, be sure that there is enough weight attached to the bottle. One of the runs shows the top of a bottle poking out of the water. This isn't very safe, because if you can see the bottle, there's nothing between you and a bursting pop bottle. The explosion was very loud. Fortunately, the bottle failed in a way that propelled it up into the air about 50 feet. Quite impressive, but loud and a little more hazardous than you want for an audience.



• The article suggests placing "ejecta" into the barrel. We tried practice golf balls. Ultimately, the surface we used was too uneven to allow for post-eruption particle tracking, but this has some interesting potential for enriching the demo with additional learning outcomes (plus, it gives students something to do while you're refilling the garbage can). I want to grab some whiffle balls of baseball and softball size and add them to the barrel. But you'll really need enough to completely cover the surface of the water, otherwise there won't really be much to see. As an added bonus, you can use the balls for particle tracking and estimate speed and size of the eruption column.



• I concur with Harpp et al. in their recommendations for a heavy-duty style, plastic garbage can. There's too much flexing and pressure to use metal or thin plastic, unless a burst and laterally-directed blast is what you want. I've used one of these garbage cans for about 10 explosions and it seems fine. The downward pressure does push the can into the ground, so avoid having sharp rocks or something like that underneath the container. They might puncture the can.



• Finally, go beyond the "big bang" and think about the physics behind this demo. Grab your ideal gas law and video tracking software. These demos used "about" 50 mL of LN2 for each explosion (the boiling LN2 makes it hard to get a real good estimate). And the can is the 32 gal size (filled with about 30-32 gal. of water each time). We can estimate height of the water column (and its approximate center of mass) and the time it took to get there.


• Some questions to consider:




• How much energy was released in the explosion


• Why does the garbage bin jump upward? Is it rebounding of the explosive force, or friction from the water moving upward, dragging the bin up with it?


• How could we rig the demo to create the largest possible eruption? (In our first series of tests, there didn't seem to be any obvious difference in column height between a 20 oz (0.6 L) bottle and a 2 L bottle.

Okay, enough thinking. On to the explosions!

Thurs-Demo: The one that should have worked last week

This demo has been a long time coming. I came up with the idea back in '97 as an undergrad. We were looking at self-organized, critical systems and the 1992 Landers earthquake was brought up as a possible system where small perturbations may be enough to generate change. So I rigged up a demo - and it worked nicely. Now, 14 years later (yeesh - has it been that long?) I have this demo-a-week thing going on and I thought it would be a good idea to try it again. Especially given the recent interest in the Japan quake, my Earthquake Machine (El Temblor!) and the current brouhaha regarding remotely triggered seismicity and earthquake predictions. But my attempt last week was less than impressive.

Soda Pop Earthquake from Matt Kuchta on Vimeo.

I probably should have also existing bubbles being shaken loose as an additional factor in causing movement.



Some background: A magnitude 7.3 (M_L) earthquake near Landers, California appears to have triggered seismicity in several locations in the western US - especially in areas with hydrothermal systems or sites with recent volcanic activity occurred such as Long Valley Caldera (Hill et al, 1993, Linde et al., 1994, Johnston et al., 1995). The epicenter of the Landers quake was several hundred kilometers south of the Long Valley Caldera - what these authors suggest is that bubbles within magma or hydrothermal systems were "shaken loose" as a result of the earthquake passing through the fluid and these bubbles created extra pressure that was exerted on the crust, inducing seismic activity.


It's interesting to note that Linde et al (1995) speculated that there may have been volcanic eruptions triggered by other regional earthquakes including 1707 eruption of Mt. Fuji (Hoei M=8.4), Mt. Calbuco in Chile - 1960 (M=8.6), and the 1980 "Pozzuoli crisis" after the (M=6.9) Iripina quake. I found this interesting, especially given the recent set of posts by Jessica Ball (Magma Cum Laude) discussing the possibility of volcanoes triggering earthquakes (Part 1 and Part 2).

Sources:

Hill et al (1992) Seismicity in the Western United States Triggered by the M=7.3 Landers, California Earthquake of June 28, 1992, Science vol. 260, pp. 1617-1623.

Linde et al (1994) Increased pressure from rising bubbles as a mechanism for remotely triggered seismicity, Nature vol. 371, pp. 408-410.

Johnston et al (1995) Transient Deformation during Triggered Seismicity from the 28 June 1992 M_w=7.3 Landers Earthquake at Long Valley Volcanic Caldera, California, Bulletin of the Seismological Society of America, vol 85, no. 3, pp. 787-795.

This is what a shield volcano looks like

(click to embiggen)

From left to right: Mauna Kea, Mauna Loa and Hualalai - the three tallest peaks that make up the big island of Hawaii. It's not one shield volcano, it's several. The currently active volcano, Kilauea, is out of view, behind Mauna Kea in this view.

Lunatic behavior

Lunatic comes from the late Latin, lunaticus. This word, as adjective or noun, pertains to being foolish, eccentric, or absurd. It stems from the ancient belief that changes in the moon caused intermittent insanity (Luna = moon). Kind of a medieval version of the "Twinkie Defense." But while changes in the moon may correlate with people acting weird (particularly those who are inclined to believe in some lunar link), there is no reason to think the moon causes this weirdness. It's in your heads, people. Erik, at the Eruptions blog, dives into this concept in great detail.

There have already been murmurings among the astrology crowd that the full moon set to arrive in a week is going to be some kind of "supermoon," capable of destroying cities, leveling whole continents to waste with earthquakes and volcanoes and über-tidal surges. Whatever. Yes, the moon's gravitational pull does cause tides. So does the sun. But connecting the moon to any specific event on Earth - especially catastrophic changes - is beyond flimsy. Imagine this: your head is Earth. Take a ping pong ball and hold it out at arm's length - this is the moon.


To represent the change in distance between the furthest and closest distances of the moon, just bring the "moon" one ping-pong ball closer. This is your "supermoon." Do you see any change in the size of the ping pong ball? Perhaps - and on a clear night, we may think it looks brighter than others. Is it? Or are you judging this based on the fact that the previous three weeks have been comparatively darker - we could measure the light levels and probably see an increase, but are our eyes sensitive enough to accurately detect the change? I'm not sure. But the change in gravitational force it exerts? Now we're looking at fractions of fractions (due to the difference in gravitational pull between the sides nearest and furthest from the moon).

In the head/ping pong model, the sun is going to be a 54-foot diameter sphere nearly a quarter of a mile away. Both of them are exerting a gravitational pull on the earth. But any effect on us, or a particular spot on the earth's crust will be tiny. Tectonic forces and gravitational forces exerted by Earth itself will be thousands of times greater.

There's also the temptation to link the eruptions in Hawaii to the earthquake in Japan. Or some other volcanic/earthquake event with another far across the globe. The unifying theory for all these events is Plate Tectonics. Not some mystical planetary voodoo. While far-field earthquakes can occur (New Madrid, for example), the idea that an earthquake on one side of the globe will cause volcanic eruptions on the other - or some (by gravitational standards) tiny change in orbital gravitation is posing a great risk of catastrophe is ridiculous. It's like trying to pop a zit on your forehead by clenching your buttocks.