Friday, July 20, 2012

Tsunamis, Rogue Waves, and Tidal Waves

Geology started out as the science of uniformitarianism: What we could see in the rock record is what we could expect to see in the future. The initial assumption of Lyell and other early geology pioneers was that the “Great Flood” of the Bible was not to be taken seriously, and that every geologic phenomenon in the past was like what we observe today: calm and steady and slow – like weathering.  However, in the past several generations, geologists have come to recognize that there have been short-lived, phenomenally catastrophic events that have changed the face of the landscape. One of these is the tsunami, a word of Japanese origin where it was first described scientifically. The word was chosen about a generation ago to distinguish one kind of wave event (a tsunami) from a tidal wave or a hurricane storm surge. A tidal wave is a twice-daily feature associated with Lunar and Solar cycles. In Southeast Alaska and the Bay of Fundy in eastern Canada, these can reach 15 meters in height – especially if focused into an east-west-oriented narrow bay or fjord such as at Fundy. A “tidal bore” is a wave that moves in with a rising tide, and in shallow estuaries like Turnagain Arm in Southeast Alaska, these can be walls of water several meters high – sufficient to overturn or “pitch-pole” a medium-sized boat.

What causes tsunamis? Can one happen in the US?
-Jared W

There are four different kinds of events that have caused tsunamis in the past:
1.       Asteroid impacts. There are huge tsunami deposits on Haiti stemming from an asteroid impact 65 million years ago.  This was the dinosaur-era-ending Chicxulub asteroid, which impacted on what is now a small village of that name on the northern tip of the modern Yucatan peninsula of Mexico. Fragments of this explosion apparently also went sub-orbital and landed as far away as Montana and the mid-Pacific ocean. Estimates of a mega-tsunami wave in the Caribbean up to 3 kilometers in height have been suggested – enough to completely inundate a large island such as Madagascar.

2.       Landslides. The face of a mountain fell off into Lituya Bay in southern Alaska in 1958. It created a wave at least 500 meters high, judging from surrounding mountains stripped of trees to at least that elevation. Surviving witnesses describe their vessel being floated over a large raft of logs, and the modern coastline remains largely denuded.

3.       Volcanoes. When the volcano Krakatau exploded in 1883, 45-meter-high waves reached as far as 10 kilometers inland on Sumatra, and swept people, animals, and debris back into the Sunda Strait. More than 36,000 people died in this event, and contemporary descriptions report that a person would walk across the Sunda Strait on bodies and logs without getting their feet wet. The tsunami from the catastrophic eruption of Thera volcano (modern Santorini in the Aegean) 3,500 years ago apparently ended the Minoan civilization on nearby Crete. The language of modern science is substantially Greek-based (with Latin) as a result of that single event.

4.       Earthquakes. In January 1700 AD, a subduction earthquake in the Cascadia region of northwestern North America sent a tsunami across the Pacific Ocean that devastated villages on the Sendai coast of Japan. The earthquake sunk a forest in Puget Sound below sea level. The wave that reached Japan was called the “Orphan Tsunami”, since it was not associated with any locally-felt earthquake or typhoon – it arrived without warning under a clear blue sky. In 1946 a subduction earthquake off the Chilean coast of South America caused what one geologist friend referred to as “unplanned urban renewal” many hours later in Hilo, Hawaii. I have personally seen signs marking the wave run-up on telephone poles 5 meters above my head in the modern downtown area. The Great Sumatra Earthquake of December 2004 killed over 250,000 people from Indonesia to India. The wave reached Sri Lanka many hours after it was initially triggered, but there was no infrastructure in place at the time to warn the millions of affected people in its path. The Great Tohoku Earthquake of 2010 triggered a tsunami that devastated northeastern Japan, directly led to a melt-down at the Fukushima Dai-Ichi nuclear plant - and destroyed docks and ships many hours later on the Oregon coast.

It is important to understand that relatively few earthquakes cause tsunamis. The basic requirement is that the causative fault must have a normal or reverse component to it - part of the seafloor must drop or lift suddenly. Modern tsunami warning systems are based on a two-tiered approach: an initial earthquake beneath an ocean floor or ocean margin is detected. If the fault system is well known (for instance is understood to be a subduction fault), then an initial warning is issued. Deep ocean buoy systems are then monitored – these waves may travel at more than 500 kilometers per hour, so they take a relatively long time to cross an ocean. If a wave-front is noted passing through this system, then warning sirens light up on the threatened coast.

Technically, hurricanes (Atlantic Ocean) and typhoons (Pacific Ocean) do not cause tsunamis, but they DO generate low-pressure-driven storm-surges that could top 10 meters above normal sea level in the worst cases. These are not sharp-edged waves like a tsunami, but instead are long-wavelength, very broad surges of seawater tracking the eye of the hurricane or typhoon as it hits land. Hurricane Katrina in 2005 did most of its damage with a huge storm-surge that overwhelmed the levees and barriers designed to protect New Orleans, a city that over time since its founding has sunk below sea level.

There is another class of large water waves called “Rogue” or “freak” waves. There is a long history of “disappeared” ships in the history of humankind, and anecdotal stories of waves exceeding 30 meters in amplitude that somehow left survivors. Recently, sea-height-measuring radar satellites have allowed this sort of feature to be quantified. The physics concept of constructive interference of waves comes into play, but there may also be other factors involved, including diffractive focusing and non-linear effects. For instance, the southwest-flowing Agulhas current in the western Indian Ocean has long been known to interfere with westerlies to create a zone of dangerous rogue waves of unusual frequency and intensity.

By the way: that Biblical story of the Great Flood? As scientists we must be careful and not just dismiss something out of hand - like this one was. Geologic evidence now suggests that the Black Sea was a huge, populated continental basin that flooded catastrophically around 5,600 B.C.E.  
- due to waters from the Mediterranean Sea breaching a volcanic sill in the Bosporus Strait.

Wednesday, July 4, 2012

Get the Data. Don't get Killed.

There are different risk-factors that come with different life-callings:
  • Fish for King Crab in the Barents Sea: unusually high risk of becoming crab food.
  • Transport cocaine from Colombia to Texas: unusually high risk of being beheaded.
  • Fight forest fires: unusually high risk of joining the Bar-B-Que and burning with the trees.
  • Work as an accountant: Live Long and Prosper!
There have been several questions directed at us about safety while working as a geologist or geophysicist. These increased, as expected, during the 2004-2006 eruption of Mount St Helens. In a previous response to a question, I mentioned walking out the leading edges of moving lava flows in Hawai'i. This was not done casually, but to gain a clearer understanding of how these flows move - and why they suddenly can inundate towns like Kalapana. If we understand how lava creates its own new topography, perhaps we can predict where the Danger Zones are. 

This has non-trivial real-world consequences: if you build in Zone 1 or Zone 2 your home-owner's insurance will be phenomenally high, if you can get it at all.

In a larger sense, however, this opens the broader issue of inherent risk that comes with certain jobs - and how you can manage those risks.

In 1977 a young USGS geologist named Cynthia Dusel was part of a mapping team, surveying the Big Delta Quadrangle in east-central Alaska, when she was attacked and mauled by a bear. She survived, but lost both arms. Since then she has married, had a son, and even served as acting chief of the Western Mineral Resources team in Menlo Park, CA. She's something of an icon among us in the USGS: very matter-of-fact about her disability, very upbeat, great sense of humor - and epitomizes indomitable courage. 

The response to that attack within the USGS was probably predictable: everyone going up to work in Alaska started packing huge guns. Then the scientist in the Survey scientists stopped and many of them thought about it a bit more. Let's gather data about the real threats to geologists working in Alaska! they said. They did... and were surprised to learn that bear attacks came in as Number 7 on the list. Shooting yourself with your own weapon came in Number 3 - and this led to the development of a sophisticated 3-day weapons safety training course (informally called the "Bear Blasting" class) required of anyone planning to work in Alaska. Number 2 was helicopter accidents - my first USGS boss was killed in Ketchikan harbor this way. And this led to careful "carding" of pilots and mandatory training of geoscientists, so that none of us ever worked with a pilot with less than 5,000 hours of flight experience, for instance.

Number 1 was drowning. That's right: drowning. If you fall into deep water in Alaska (and southeast Alaska and the Aleutians are mostly islands, anyway), your arms will essentially stop working after about a minute unless you are wearing a Mustang suit. That's hypothermia for you. I came within a hairs-breadth of becoming one of those drowning statistics in Klawock in 1995.

It became a growing part of our scientific tradition: we all loved working in the field, but it carries with it different dangers. Soooo... how can we minimize these? How can we manage these risks?

That's a pretty crazy account.  It's particularly funny to think about your work when I think of it in comparison to our OHS (occupational health and safety) officers who come around to inspect our offices periodically to make sure that our chairs are properly aligned to make sure that we don't hurt our backs by sitting all day long.  Why in the world would you be stomping around an area of jungle amidst fresh-flowing lava?  - Lisa W.

Throughout my professional career I've faced many rather disparate dangers. This wasn't done for the adrenaline thrill - it's the only way in most cases to acquire the crucial data that we need to solve real world problems. In the Continental US, this usually means working in really rugged terrain. I camped overnight with a geophysical crew inside the crater of Mount St Helens in 2007. I had helicoptered in with some geophysical equipment, but after several days had to get back to the office before the end-of-week scheduled helicopter flight. A case in point: I planned for it, and walked out. However, it proved to be far more rugged terrain than I had anticipated in my planning (which was done with 10-yr-old air-photos in a terrain that is unconsolidated, and evolving nearly every day). If I had not been carrying (and using) hiking poles with my pack, I wouldn't be wearing these front teeth today. I still sustained permanent damage to my left big toe and my right knee in the ~20 km walk-out (the knee is still swollen as I write this).

In Venezuela, my personal journals have WAY too many "I was nearly killed again today" entries. That was the first time I really looked at the full array of danger that comes with working in the deep jungle. Initially we went down for a three-year assignment to map the roadless, jungle-covered southern half of Venezuela thinking the the big risk was from snakes. In fact, I encountered a Bushmaster on my very first Entrada. It took awhile to recognize the more subtle, even hidden dangers: testosterone-poisoned pilots, poorly-maintained helicopters, Chagas disease, piranha in all the rivers, etc. The Number 1 killer? The Anopheles mosquito - the vector for Plasmodium Falciparum, also known as cerebral malaria, followed closely by drunk drivers. I lost two of my best friends in Venezuela, in separate incidents, to drunk drivers.

After a series of very close calls I took the Advanced Trauma Life Support training at the University of Maryland medical school (yes, it's supposed to be for medical doctors - but I have the certificate to prove it). I discussed the issues with some more experienced field geologists and began instituting some safety protocols for the mapping mission that I was in charge of - for instance we almost never used helicopters after the first year there. We wore light-colored clothes to minimize being targeted by Africanized bees. We always walked the picas (trails) in pairs. We always insisted on mosquito nets surrounding our hammocks, etc. One of my colleagues instituted one safety protocol himself: he bailed out, breaking his contract and leaving his commitments on my shoulders. I've never begrudged him for this by the way: he was one really, really frightened dude. A year later he even left the geosciences profession, abandoning his PhD training, to become a financial advisor. Live long and prosper.

But here's the thing: you CAN control the variables, you CAN push the statistical envelope far over to the likely-to-survive side of the Gaussian probability curve. 

I took some training last year that is a case in point. You can't study a volcano unless you can get a lot of equipment up INTO it. My sons will attest that just getting 300 kilos of gear up into the Pumice Plain (the Mount St Helens Blast Zone) for their mom's Masters Degree research project was a non-trivial exercise. It's much harder to do this in the upper edifice of the volcano - so we use helicopters.

Easy to say, technically hard to do.

The safest way to ensure the survival of the helicopter and pilot is NOT to have a lot of loose shovels, antennas, and batteries INSIDE the ship. This little nugget of wisdom was culled by carefully gathering reports of all helicopter crashes in the United States over 50 years. Instead, you *sling* all that loose, sharp-edged junk. There is an electrically-controlled hook on the belly of most helicopters. We took a full day to practice this routine on a level lawn:
  • Gather all your gear in a pile, weigh it piece by piece. Give that manifest to the pilot - who will do a calculation to see if he can even lift it to the elevations you will work at AND have enough margin to carry you along with it.
  • Load it into a net that itself weighs 25 kg. Try to balance that net, arrange it so things tilt inward, and especially be sure that nothing is sticking out of the net that could tangle with anything - like you, or the skids.
  • Then call the helicopter in to you, holding your hands up and out in the direction of the wind (we usually dangle a strip of red flagging tape so the pilot can judge the local wind velocity).
  • As the ship approaches, it comes in slowly at about 1.5 meters off the ground - remember that the thing is wobbling around in the wind as the pilot tries to control it against the volcano-heat-triggered turbulence, and it is SCREAMING SO LOUDLY that you can easily get rattled just by the 140-db sound (we wear helmets with ear protection, but it's still unnerving).
  • You must then walk under this shuddering, screaming thing, hook your sling net to the belly, and then carefully back out (NOT turn around), without tangling your feet in the net, and keeping your footing amid the rocks and talus.
  • Above all, if you stumble, you must NOT grab one of the skids to regain your balance. If you do, the ultra-light craft will flip, the blades will hit the ground, and all that angular momentum must go somewhere really, really fast – and you will both probably die. You have to trust the pilot, and he must trust you: if you hook the net wrong, or inadvertently tangle it in one of his skids, it could kill him. The craft is so fragile that you can literally push it around in the air above you with your hand... but those screaming turbines mean it is powered by 600 horses. Everything spinning is so finely balanced that if a blade nicks a branch it will chip a chunk off – and it then becomes hugely unbalanced. Then the angular momentum comes into play, and the aircraft will literally beat itself (and its occupants, and everyone within 20 meters) to death.
When a helicopter goes down, that's just the beginning of the bad stuff... think of the old high-school joke: What's red and green and goes round and round real fast? A frog in a blender. Now imagine doing this sling exercise on a steep ridge with 30-knot wind gusts.  THAT's why we practice and practice all day long on a lawn to do this right. So it's reflex.

Live Long and Prosper. And still enjoy the Adventure!