Sunday, January 30, 2005

Adulation! Praise!

...well, faint praise at least. OK, well maybe it's just a link. But links are what bloggers crave.

It looks like ::dura:mater:: is being used again as an example of technical writing in a course that has students set up blogs. This time it's Douglas Eyman's WRA 110 'Writing About Science and Technology' at Michigan State University.

There are links on the page to some of the student blogs, which not surprisingly are better laid out and written than this one. After all, they are being professionally trained. And graded. I had an interesting surf through them.

 Thursday, January 27, 2005

Tsunami threats in North America:

Excerpts from a recent Press Release on expert witness testimony before the House Committee on Science:

"Brigadier General David L. Johnson (ret.), Assistant Administrator of the National Ocean and Atmospheric Administration (NOAA) and Director of the National Weather Service (NWS), said that between 1900 and 2004, 923 tsunamis struck the Pacific Ocean, 120 of which caused casualties and damage. 'Furthermore, there was no single year during this period that was free of tsunamis,' he said.

Dr. Charles 'Chip' Groat, Director of the U.S. Geological Survey (USGS), told the Committee that there is a 10-14 percent chance that the Oregon coast will be hit by a tsunami comparable in size to the one that recently hit South Asia within the next 50 years."


While the current focus on tsunami threats is mostly in the Pacific because of the amazingly high frequency of tsunamis there (923 tsunamis in 104 years!), the threat to the Atlantic coast is just as real - although less frequent. Most of this difference in tsunami frequency has to do with how plate tectonics controls what happens at the edges of the two ocean basins.

Here's why: first, remember that the total surface area of the Earth does not change. This means that when seafloor is created somewhere (for example, at a mid-ocean ridge), then an equivalent area of surface has to be destroyed elsewhere. Surface is in fact destroyed in subduction zones (see the post below on the Asian tsunami for a diagram of subduction).

The Atlantic has relatively gentle tectonic activity on the mid-Atlantic Ridge where the seafloor is spreading, pushing the Americas away from Europe and Africa. The Pacific, on the other hand, is bounded by subduction zones, where a lot of seafloor is being destroyed. Subduction is a generally more violent process that generates the great earthquakes - 1960 Chile, Alaska 1964. Aside: subduction also creates lots of volcanoes, and this leads to the "Ring of Fire" that has been so often mentioned, and confusingly associated with tsunamis.

So - one can expect that each ocean's tsunami frequency from subduction earthquakes varies with the amount of subduction going on at the boundaries of that ocean. And that is the case: There are more of these types of tsunamis in the Pacific Ocean, less in the Indian, and even fewer in the Atlantic.

However, there are other sources for tsunamis. You could think of subduction-generated tsunamis as what happens when you tip a tray of water - but you could also dump something into the tray and cause a wave, set off a firecracker underwater, or hurl a ball into the tray. Many of you have probably seen video of the glacier disintegrating in a Greenland harbour that causes a massive wave, or the calving glacier that causes a wave that drowns several unfortunate spectators. Landslides fall into this category of sources, and in fact a landslide was the source of the highest tsunami wave witnessed, about 500 meters (!), on July 10 1958 in Lituya Bay, Alaska.

Landslide-generated tsunamis are the main threat in the Atlantic. There are several places being looked at as possible sources - the main one being the Cumbre Vieja volcano in the Canary Islands. It is quite common for volcanoes to split off large parts of their flanks, which then slide off, either very gradually, or very suddenly. If Cumbre were to let go suddenly, models indicate that a 10 to 25 meter high wave would reach the Eastern Coast of North America within a few hours. So much for Miami, Charleston, Washington, New York, Boston, Halifax, etc. etc.

The other landslide threat is the large pile of sediments that build up at the mouths of rivers, or at the edge of the continental shelf. There are large sediment piles long most of the East coast of the US, built up by the erosion of the Appalachian mountains - sonar surveys over the deeps just outboard of the shelf show several places where enormous landslides have spread out many miles onto the seafloor. The Albemarle-Currituck slide is thought to have occurred about 18,000 years ago, and almost certainly caused a devastating tsunami along much of the mid-Atlantic coast. The tsunami waves probably carried several miles inland, and certainly penetrated along the larger rivers and bays of the region.

Another source for tsunamis is an underwater explosion - the firecracker I referred to above. Just about everybody has heard about the August 1883 Krakatoa eruption, which generated a considerable wave in the Sunda Strait. The closest large town, Merak, faced a catastrophic 35 meter high wave. There is not much threat for this type of eruption for the volcanic islands in the Atlantic off the African coast. Wrong type of volcano.

The last threat (and this applies equally to all oceans) is from an asteroid impact. If something large does a belly-flop into the ocean, it causes a large wave. I have addressed the threats to Earth from these types of collisions recently, and they are minuscule.

The source of the next East-coast tsunami will be either a volcanic collapse or a submarine landslide. When? Maybe tomorrow. Maybe several thousand years from now. But it will occur someday.

Labels: ,

 Tuesday, January 25, 2005

Krulwich on NOVA:

Hmmm. Some good TV on tonight...

PBS is premiering NOVA's new show, scienceNOW, and there's even going to be a piece about booming sand, a topic which has appeared here before...

Tune in, kids!

 Tuesday, January 18, 2005

Endurance of Opportunity:


Posted by Hello

This is a picture of something any sedimentologist would recognize as a classic example of either cross-bedding or an angular unconformity (thanks to Ian Carr and Jackie Huntoon, who sorted out my misconceptions here...).

In cross-bedding, an advancing dune lays thin layers at an angle ('foresets') on its down-current face. This can be caused by either wind or water. The foresets are usually quite thin, and often occur in sets of sets, between bedding planes that are (or were) horizontal. Unfortunately, we can't see much lower - the section is buried in debris at the bottom.

In an angular unconformity, the lower layers (to the lower left in the frame) would have been laid down, tilted, and then eroded, cutting across the bedding (the diagonal discontinuity). The upper layers (in the upper right of the frame) were then laid down on top of this new surface. This is usually interpreted as physical evidence of at least tectonics and erosion, very possibly water-related.

These processes are common enough on Earth, but this is the Burns Cliffs inside Endurance crater on Mars. I'm amazed this didn't receive more press time than those incredibly cryptic "blueberries."

I'm sure that someone out there is doing numerical modeling of cross bedding for Mars, because there are a whole different set of physical constraints - different gravity, different viscosity of the air, windspeeds, etc. A lot of money has gone into this modeling for Earth, because of the oil industry, so there are probably a lot of starting points for budding Areologists...

Here is a (very large) image of some great soft sediment deformation - usually interpreted as a stream or river deposit, or at least a lake bottom with active slumping going on. The famous "blueberries" are quite prominent here - they were at first thought to be spatter from eruptions or impacts (like tektites), but some of their settings convinced the mission scientists that they were formed in place as concretions. Other physical evidence for water was the presence of vugs, or cavities where a crystal of some mineral deposited was later dissolved, leaving a hole.

It is very likely that similar cross bedding features exist on Titan, since there are liquids, winds, and enough body size for tectonics. However it is doubtful that we shall ever see them, since Huygens had no way to get around, much less usable battery power to do so. It was a feat just to get there and sit crippled on the surface while freezing to death.

...and yes, I feel sorry for the poor thing. I've felt sorry for them before (1, 2).

 Monday, January 17, 2005

Zing!

Heard at a recent meeting:

Head of Programming for the Weather Channel: "What do you think about the future of the media?"

Head of Research, Xerox: "You will be out of business by 2010."

 Friday, January 14, 2005

Cassini, Huygens:

Huygens is on the surface! Blocks of ice (?) litter the surface in this raw DISR image from the surface of Titan, 67 light-minutes distant from us. Luckily the lander was not toppled over and unable to point its uplink antenna... what I noticed was the rounded nature of the rocks. Also, very much like Mars, isn't it? Even with such different surface composition and temperatures!

ESA Cassini-Huygens website Posted by Hello

Cassini, Huygens:

First image of the surface of Saturn's moon Titan from the Huygens probe. Prominent are the dendritic drainage patterns that appear to head off to the upper left, and what appears to be a remnant crater in the center of the scene. The contrast between the light left and darker right side is not yet understood - perhaps even a shoreline with some islands, but the center of the scene is definitely a solid surface, upon which the probe appears to have survived at least two hours, transmitting data to Cassini above.

Image is a screen grab from NASA TV transmitting from ESA HQ in Darmstadt, Germany. Altitude of lander about 16.2 km, leading to a pixel size of about 40 meters. The quality is so bad that I am reminded of the Mariner Mercury shots... expect better quality soon. Posted by Hello

 Wednesday, January 05, 2005

Watson & Crick:

...never dreamed of this.

On August 8 last year, a group of tourists were enjoying an afternoon aboard a Chicago Architecture Foundation tour boat. The Architecture River cruise takes a 90 minute ride along the Chicago River, viewing the details of over 50 famous buildings.

However, on this day, the tourists got more than they expected. As the boat passed under the Kinzie Street bridge, a passing tour bus emptied its bathroom waste tanks through the grating onto the helplessly upturned faces below. One hundred nine people, including several children and an infant, were showered with, um... sludge.

Surveillance cameras indicated a bus with characteristic markings was the only one to cross within 15 minutes of the incident, and descriptions from those passengers who could still see narrowed down the the bus to one chartered by the Dave Matthews Band.

The band was of course highly concerned, stated they were not on board at the time, that they trusted their long-time driver, and that they stood by his statement that he had nothing to do with the incident. In a public statement, the band members offered their DNA to prove that the offending items were not their droppings. The band later offered a $100,000 settlement for the passengers before results of the DNA test were divulged.

The case comes up before a judge next Friday, January 14th. There is no statement yet from the Illinois Attorney General's office regarding the results of the DNA test.

Moral - always be careful where you s#!t (or speak). Someone may carry it away and throw it for you. And it carries your characteristic stink, wherever it ends up.

Labels:

 Monday, January 03, 2005

von Muggenthaler:

My nuggets of learning today were:
  • Giraffes are not mute. We just assumed they were because we couldn't hear them. They emit sounds below our range of hearing.
  • Tigers emit infra-sound that can make you (and presumably their prey) go numb.
  • Cats purr in a range that promotes healing


My non-serious nugget is that Kyle the Kangaroo nearly beat out Tony the Tiger to be the Kellog's Frosted Flakes spokes-animal in 1952. Kyle must have been paralyzed during the reading by Tony's 18 Hz growl, which the casting director couldn't hear. I'll have to try growling really really low during meetings here and keep track of the results.
--
...not sure that worked. I just got a little more personal space as people backed their chairs away from me.
--
Now I'll try it in the subway. Tune in tomorrow.