disasters by the dozen-- steven n. ward tsunami, landslides, dam breaks & floods ·...

Disasters by the Dozen--Tsunami, Landslides,

Dam Breaks & Floods

Steven N. WardInstitute of Geophysics and Planetary Physics

University of California Santa Cruz

FOP, Walker Lane NV 9/17/10

Monday, September 20, 2010

Tsunami Science - A sleepy field ….


BULLETIN

PUBLIC TSUNAMI MESSAGE NUMBER 1NWS WEST COAST/ALASKA TSUNAMI WARNING CENTER PALMER AK 833 PM PST FRI JAN 12 2007

AT 823 PM PACIFIC STANDARD TIME ON JANUARY 12 AN EARTHQUAKE WITH PRELIMINARY MAGNITUDE 8.4 OCCURRED EAST OF THE KURIL ISLANDS RUSSIA. THIS EARTHQUAKE MAY HAVE GENERATED A TSUNAMI. IF A TSUNAMI HAS BEEN GENERATED THE WAVES WILL FIRST REACH SHEMYA ALASKA AT 934 PM AKST ON JANUARY 12. ESTIMATED TSUNAMI ARRIVAL TIMES AND MAPS ALONG WITH SAFETY RULES AND OTHER INFORMATION CAN BE FOUND ON THE WEB SITE WCATWC.ARH.NOAA.GOV.

...A TSUNAMI WARNING IS IN EFFECT WHICH INCLUDES THE ALASKA COASTAL AREAS FROM NIKOLSKI ALASKA TO ATTU ALASKA...…A TSUNAMI WATCH IS IN EFFECT FOR THE ALASKA COASTAL AREAS FROM SEWARD ALASKA TO NIKOLSKI ALASKA...…

AT THIS TIME THIS MESSAGE IS ADVISORY ONLY FOR OTHER AREAS OF CALIFORNIA - OREGON - WASHINGTON - BRITISH COLUMBIA - AND ALASKA...

Tsunami Hazard - A sleepy field …. with rude awakenings


Tsunami waves have far greater period, faster speed, and longer wavelength than familiar beach waves

In deep ocean, a 10m wave rising over 50 km is as flat as Kansas.

Ships at sea don’t see tsunami. Note flat and steep parts of top curves. Flat parts=wave stays tight; Steep parts=wave pulls apart


Unlike regular waves, tsunami reach all the way to the sea bottom.

Generate Bedforms

--You can’t out dive a tsunami.

Tsunami move the ocean differently than regular waves seen at the beach.

Tsunami Waves Regular

Waves


Tsunami slow and grow as they near the coast.

In deep water

V~500 mph

They come ashore about 20-30 mph.

Still -- Can’t outrun one to high ground.

Grow by 3-4xTsunami Shoaling Wave Period=150 s

Shallower water= Shorter wavelength


Best description: The ocean turns into a river ………….a river flowing right toward you.


Best description: “The ocean turns into a river.” ………….More Flood-like than Wave-like.

At 20 mph, water exerts

~800 lbs/sq ft P=ρwv2 /2

In 10,000 years geologists might dig down here and find a “Smashed Car Deposit”. Smoking gun of a paleo-flood. Monday, September 20, 2010

How Do Tsunami Get Started?1) Disturb the sea surface.

Say, Drop an Asteroid in the Ocean.


You might think asteroid impact is crazy, but there are ~175 known impact structures on Earth

Like many things in nature, asteroids follow a power law distribution of size versus number. D~3-4 m is Annual Event (Fireball)

D~50m 500y Event (Tunguska Level 1908)

D~500m 100,000y Event

D~5000m 20,000,000y Event (~Extinction Level)Monday, September 20, 2010

We have some feeling for impact-like effects from nuclear tests.

Baker Test: 1946

Bikini Atoll, Y=23Kt

Cavity Diameter ~ 1000 feet

Local Tsunami Height ~100 feetMonday, September 20, 2010

The biggest of the N-tests hardly holds a candle to even a “smallish” 500 m diameter asteroid at 40,000 mph.

Energy=9400 Mt = 400,000 x Baker Test

Blows a hole in the ocean about 12 km across.

If they hit in deep water, Wave heights from asteroid impacts can be 1000 meters locally

Impacts of this size happen about every 100,000 years.


Propagation of tsunami beyond the cavityis not widely in dispute. Tsunami waves crush together in the shallows and “bend around” obstacles. Watch out Ireland!

Impact tsunami are very dispersive. Long periods travel faster than short periods. Dispersion reduces impact tsunami size with distance faster than EQ tsunami.


Historical Example �� Asteroid Eltanin Diameter: 1100mWhen: 2.15 Million Years Ago. Where: South Pacific

Impact Tsunami this large potentially affect entire ocean basins

Evidence of impact found D.S.D.P. Cores.

Deposits in New Zealand or Australia?


WHERE NEXT?��Asteroid Apophis Diameter: 350m Discovered: 12/26/04

Passes <30,000km from earth in 2029!!

Current Projected Earth Impact probability:~1/200,000

On April 13, 2036

In terms of “Predictability of Natural Disasters” asteroid impacts can be one of the easiest to quantify -- Example: Asteroid 1950 DA has a 0.3% chance of Earth Impact on March 16, 2880.

No kidding.


Mark Twain says:

“Everyone talks about natural disaster, but no one does anything about it.”

Asteroid Defense-

Time Before Impact and Controllability primary issues.

1) Gravity Tug

2) Kinetic Impact

3) Standoff Explosion

4) Surface Explosion

Apophis Impact Scenario: North of Panama Expect: 20m+ waves onshore Est. Infrastructure loss: 400 Billion US$


Certain explosive volcanoes can be considered as “impact-like” sources for the purpose of generating tsunami.

You can get an equivalent tsunami energy from the diameter and depth of the caldera.

Explosive Sources=Uniform Radiation PatternMonday, September 20, 2010

Santorini Tsunami is often cited as contributing to the downfall of Minoin Culture ~1600BC and the “Atlantis Story”


How Do Tsunami Get Started

2) Disturb the sea bottom, transiently Say, run a Landslide.

As material moves along the seafloor, the water must go UP, DOWN, or AROUND. This makes waves.

Landslide tsunami can be very directional.

Whether a solid block or a disintegrating gravel pile, the process is the same.


Typical Situation:

Slide material falls from high on a slope,

possibly far under water.

The process stirs tsunami waves on the surface of the ocean.

This could be any continental slope.

Real world landslides are complex. We need good deposit mapping to make good tsunami

modelsMonday, September 20, 2010

Submarine landslides come in all sizes, and they occur on both passive and active continental margins.

Many slide scars are found on continental slopes and on sides of submerged river canyons.

Simulation of 0.1 km3 slide in Monterey Canyon, California. Simulation of earthquake-induced slides

in Pacific NWMonday, September 20, 2010

Some of the largest landslides originate from the collapse of volcanoes.

Remember Mt. St. Helens in 1980 (~3km3)

Imagine the tsunami if this happened in or near the ocean! Fact is, such things are fairly common, geologically speaking


Prehistoric Example.

Italy’s Mt. Etna (below).

Landslide Simulation for 8ka event

Note multiple braided flow paths. If you observed this deposit years later, would you consider it a single event? Perhaps not.


A several km3 slide can make waves of a few meters to tens of meters high regionally. Mt. Etna example.


How do we know such large tsunami exist? Doubting Thomas-”I haven’t seen it so it can’t happen.’

Geologist- Lot’s of things I haven’t seen myself, but indirect evidence may exist. Ex. Plate Tectonics. In our case Tsunami Boulders

It’s one thing to be cautious, it’s another to be closed all together.

F.Y.I. A roundish boulder 8 m diameter can be tipped by 10 m/s flow.Monday, September 20, 2010

While the Ritter Island Event was Impressive at 5 km3 (Mt. St. Helens size)

Far more Gigantic landslides have occurred in Geological History

In the past 20 million years, the Earth has experienced scores of landslides 10, 100 or

even 1000 times larger!

Waves from such superslides are called “Mega-Tsunami”


The Canary Islands have experienced

about a dozen superslides in

the past 2 million years.

Where Next?

How do we know this?

The slide stuff is still lying there!


years ago.

According to Dr. Simon Day, the

mountain is primed for

another show.

Expected to drop as much as 500 km3

into the deep Atlantic

Basin-- about the same as

last time

Volcano Cumbre Vieja on La Palma Island last collapsed 550,000


When this happens--

STAND BACK

The slide will release

about 3x1019 J of

energy.

Roughly equivalent

to detonating the entire

world’s nuclear weapons stockpile all at once. 8,000 Mt.Monday, September 20, 2010

Only about 10-15% of slide energy goes

into tsunami, but still...

Within 20 minutes, a wave will wet local islands to 150+ meters.


A La Palma Tsunami will affect coasts along entire Atlantic Basin.

Lisbon 40m Ireland:40m Florida:30m NYC:25m Brazil:40m

Not just one wave. WAVE SET UP Storm surge-like


One 10m high wave - coming in to Cape Cod

Flooding several to many miles inland.

Nantucket folks will not be happy.

A LA PALMA TSUNAMI WON’T BE THE END OF THE WORLD, JUST PRETTY EXCITING.


Some tsunami start from trans-shore landslides into oceans, lakes and fiords. Most everyone has heard of the Lityua Bay Alaska tsunami of 1958. A quake-induced rockfall pushed water 500 m up the opposite slope.


First Step: Model the landslide. Typical behavior: From block-like sliding to debris flow


Second step: Input landslide model to drive the tsunami. 500m splash is met.


“Escape from Lituya” Best Action Adventure Film of 2009Monday, September 20, 2010

Landslides into Lakes make tsunami. Consider Lake Tahoe.

Bathymetry shows unmistakable evidence for a large landslide from west shore at 7 -15ka. Big blocks thrown everywhere.

Maybe Geological Evidence for a Flood down the Truckee all the way to Reno?


Simulation of 5.5km3 Lake Tahoe Slide

Certainly gives favor of the event. Southern portion of western shelf collapsed. Northern part still exists.


Tsunami simulation. (Fancy animation by Steve McQuinn.)

If the shelf to the north near Tahoe City collapses like the southern piece did, then say goodbye to all those Million Dollar Homes!


1889 Johnstown Flood

In 1889 Johnstown was a Gritty, workingman’s town on flat piece of ground at a river junction. Note infill of drainages.

With iron ore, coal and railroads nearby, perfect location for steel mills.


About 50,000 folks crowded the narrow Conemaugh Valley. Most lived in cottages rented from PRR and Cambria Steel.

Being in a flood plain, Johnstown flooded most every year, but it was never a big deal, however 22 km upstream from the city and 150 m higher lay South Fork Lake…..


The lake was created as a summer retreat for wealthy Pittsburgh Industrialists. Close to home/office. Easy railroad access.

Lake was held back by a 22 m high reconstructed dam originally built for the Portage Railroad in 1858. 16 million cubic meters. Any one heard of the Portage Railroad? You could take a boat from Philadelphia to Pittsburgh across the Appalachians!


At 3 PM May 31, 1889 after some of the heaviest rains in memory, the dam overtopped.

Within five minutes a 100 m hole opened in the 200 m wide dam.

Lake drained completely in about one hour.

Remains of the dam are still there today.


Flood water 7 m deep cut across Johnstown about 60 minutes later.

Houses were picked up whole and floated down river – families and all.


Nearly everything in the valley was smashed and burned at the Stone Bridge below town.

Some 2600 people were lost. Until 9/11 this was the largest single disaster in US history.

Bodies were later found as far away as Cincinnati!


From a simulation point of view, lots of information to work with -- Historical accounts, inundation maps, PRR investigations, etc.

And as I said, the dam remains are still there to fix breach size, etc.


Why do simulations?

(1)Lots of good information comes from a Physics Based Simulation. Information that was not or could not be measured.

(2) Simulations tie together observations that seem unconnected.

(3) You can investigate “want if” situations.

(4) Sims look darn cool!


You Tube Movie.


Anyone recognize this dam?


St. Francis Dam. 1928. Near Castaic California. Part of the Los Angeles Aqueduct Project. 45 million cubic meters.


Somebody messed up big time!

CA required Engineers to be licensed from then on.

It suffered complete collapse less than one week after first filling.


Bits of the dam carried down stream. Similar situation in natural floods.

One can calculate flow depth/speed from boulder size & shape.


Simulation of early events. Reservoir drains to creek bottom in about one hour.


Flooding down Santa Clara River past current “Six Flags” Park. I-5 crosses just here.

Took about 6 hours to reach the Pacific Ocean.

600 fatalities.


Please watch my YouTube. Ken Burns has nothing on me.


So why all this talk about dam breaks?

In the valleys of Basin and Range around here many paleo lakes have come and gone.

Some may have drained very quickly after breaching a natural barrier so the comparison to dam break calculations are quite appropriate.


Take Lake Wellington in Smith Valley. To explain certain terraces, this lake may have formed by a temporary landslide dam across its narrow outlet.

If a dam had once blockedthe valley -- How much water did it hold? How long might it take to fill? If the dam were to burst suddenly, What would the flow rates be and How long would the flood last?


Before doing a full scale simulation, let’s consider a simple approximation. The Weir Problem.

We have a container with a hole at depth h,anybody know the velocity with which water will exit the hole?


Let’s turn the nozzle straight up. Stands to reason that….

If you throw something up at velocity V, it will reach max height hF = VtF-(1/2)gt2

F in tF seconds tF=V/g . So if hF =h thenV = sqrt [2gh].


To get lake drainage rate versus time need to:

(1) Reduce lake volume by current flow rate F(t)dT (2) Find lower lake height H(t) given current lake area and volume lost (3) Update flow rate with new size/shape of breach given lower H(t) (4) Repeat till there is no water left.


In this case, the dam is trapezoid shape Wtop=225mWbot=45mH=75 m

Initial volume is 8.8 billion m3. [Other dam break examples were 16 and 44 million m3]Initial flow rate is 145,000 m3/s


“Weir Theory”Simulation ofThe draining of Lake Wellington.

Naturally draining is fast at first, then slows.

Lake now is divided into two basins, northern one might be isolated from the breach and remain.


8.8 billion cubic meters is 8.8 cubic km.Average river flow today is 300 cfs. Lake would take 33 years to fill at this rate.

Initial flow rate is 145,000 m3/s. Niagara Falls runs at 2800 m3/s.So we are talking about 50 times the flow of Niagara Falls. Make for quite a “Maid of the Mist” ride.

Break area is 10,125 m2, so initial flow velocity would be 14 m/s. Comparable to or faster than St. Francis break. Would expect to see lots of tossed boulders, erosion, high energy “smashed car” deposits. Did we?

About ½ the lake volume drains in the first 7 hours, 75% of lake drains in 15 hours, 90% in 33 hours and 95% in 70 hours.

33 years to fill. 3 days to drain. Cool.


I started to run a real particulate simulation of this.

Flow rates came out considerably less than the Weir estimate. (I think the DEM is too coarse.)

Still it gives a good impression of down steam flood.Monday, September 20, 2010

OK I’m Done. I hope that from the examples shown here that you agree that

Physics-based simulations can shed new, relevant and quantitative light on some of the geological information that we are seeing

here during the FOP and that

Geologists and Geophysics can peacefully coexist if not prosper together.

Thanks for Attending “Disasters by the Dozen”


disasters by the dozen-- steven n. ward tsunami, landslides, dam breaks & floods ·...

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