Lecture 8 Tsunami

ES 8001 and 7001 Natural Hazards and Society

Week 3 Lecture 8 Tsunami

“Tsu“ means “harbor”

“Nami“ means “wave”

After this lecture you should be able to ü  explain (with a few examples) the causes of tsunami

ü  describe (with a few examples) what they are like ü  describe the risks associated with tsunami

ü  discuss the challenges to adapting to them

An important distinction between normal ocean waves and tsunami: Wavelength

Tsunami wave lengths are long (up to more than a hundred kilometers)

Wind-driven waves have short wave lengths (tens of meters)

Observations to make while watching the following film clip

1)  What is the velocity of the water? Does it vary with time?

2)  What is the rate of rise of water in the river channel?

3)  What is the velocity of the water outside of the channel?

4)  How long did the flow up-river last?

5)  What happened after the flow up-river stopped?

I’ll ask you some related questions after the clip is over

The March 2011 Japanese tsunami in a river

Clicker session

Causes and characteristics of tsunami ①  Undersea rupture of normal, thrust and megathrust faults

•  2004 Indian Ocean and 2011 Tohoku

•  1933 Sanriku (normal faults)

②  Undersea landslides

•  1958 Lituya Bay

•  Hawaiian Islands

③  Undersea volcanic eruptions

•  1883 Krakatau

•  1628 BC Santorini

④  Asteroids

•  65 million year ago K-T extinction

•  Eltanin impact



•  1977 Sumba or 1933 Sanriku (normal faults)



•  Hawaiian and Canary Islands




④  Asteroids


Tsunami mimicks the rupture of sub-sea megathrust

If the rupture is 100 km wide, so is the initial tsunami wavelength

Tsunami mimicks the rupture of sub-sea megathrust

If the rupture is 100 km wide, so is the initial tsunami wavelength

The velocity of a tsunami is related to the depth of the sea

Velocity is controlled by water depth

velocity = gravity×water depth (km/hour) (m/sec2) (km)

Clicker session Students who are comfortable with basic math: Please offer to help any students who are not

Make sure you understand the answers to these questions before the quiz next week.

Animation courtesy of Caltech

John and Jackie Knill took these photographs from the beach at Khao Lak, Thailand

as the 2004 tsunami wave broke and flooded onshore.

This was the last photograph they ever took. Their remains were identified a month and a

half after they died in the tsunami.

km

The waves get steeper and higher as they come into

shallower and shallower water. Often they become a chaotic

front, like in the images below.

Wave

heig

ht (m

eter

s)

Seaf

loor

dep

th (m

eter

s)

①  Undersea rupture of normal, thrust and megathrust faults









④  Asteroids


A hydrodynamic model of the beginning of the 2004 Indian Ocean tsunami

Causes and characteristics of tsunami

Time is marked (obscurely) in the lower

left corner

A hydrodynamic model of the first many hours of the 2004 tsunami

Why did the wave travel more slowly to the east than to the west?

~1,200 km

from Chlieh et al 2007

Sudden vertical motions during the 2004 earthquake produced the great tsunami

The seafloor southwest of the Nicobar islands and Aceh rose several meters over just a few minutes …

… and the west coast of Aceh

dropped 0.5 to 1 meter

Nicobar islands

Andaman islands

Aceh

A hydrodynamic model of the 2004 tsunami overwhelming Banda Aceh, Sumatra

About 90,000 of a population of 350,000 died

6 km

For the most part, the damage had been done in

the first 15 minutes

QuickBird 23 June 2004 QuickBird 28 December 2004

The coast of Banda Aceh

before after

Examples of the power of the tsunami

West coast of Aceh province. The wave ran up the slopes more than 30 meters

Photo by Guy Gelfenbaum, US Geological Survey

West coast of Aceh province. The wave ran up the slopes more than 30 meters










④  Asteroids


Normal faults offshore Japan caused the great Sanriku tsunami of 1933










④  Asteroids












④  Asteroids


Mw7.9 earthquake

x

524 m

Hydrodynamic model of tsunami caused by earthquake-induced landslide, Alaska, 1958

Courtesy of Steven Ward, U California Santa Cruz










④  Asteroids



Sector collapses in the Hawaiian islands

200 kilometers

Singapore, for scale

The most recent Hawaiian sector collapse is called the Alika 2 collapse, on the flanks of Mauna Loa volcano

~100,000 years old Covers 4,000 km2 Volume 1,500 to 2,000 km3

Tsunami deposits 325 meters above sea level on Lanai

A wave this high is locally possible, in the case of a large volcanic “sector collapse”

http://www.youtube.com/watch?v=k8IAgUNr6x4

The ongoing collapse of Kilauea volcano, Big Island, Hawaii

200 kilometers

Singapore, for scale

The ongoing collapse of Kilauea volcano, Big Island, Hawaii

A A’

Normal faults are evidence of the incipient collapse of the flank of Kilauea volcano

Hydrodynamic modeling of the collapse of the south flank of Kilauea volcano

Courtesy of Steven Ward, U California

Santa Cruz










④  Asteroids



A large, local tsunami occurred during the 1883 eruption of Krakatau

~35,000 people were killed as tsunami up to 35 m high hit the coasts of the Sunda Strait

At least three plausible causes

3) Large volumes of volcanic material enter the sea and displace sea water

1) An enormous explosion displaces large quantities of sea water.

2) The underwater portions of the volcano subside quickly during the eruption, greatly disturbing the seafloor










④  Asteroids


Santorini

Source of the great eruption of 1628 BC

The late Minoan town of Akrotiri was buried by the

products of the eruption, but all inhabitants had already fled

Archeologists have found that the capital of the Minoan civilization, Knossos, on the nearby island of Crete was badly damaged by the

tsunami. This may have led to the rise of the Myceneans and

Greek civilization










④  Asteroids



o  A 10-km diameter meteorite struck Earth 65 million years ago and led to the extinction of about 50% of known species at the time, including most species of dinosaurs. Clear geological evidence for an immense tsunami on the coasts of the Gulf of Mexico

o  Fortunately, the average frequency of impacts is low •  1-kilometer asteroid impact occurs about once every million years)

o  1-kilometer asteroid falling into 5-kilometer deep ocean •  Would generate a 3-kilometer-deep cavity in the sea floor •  Cavity walls would collapse rapidly and generate tsunami •  Kilometer-high tsunami waves would cause immense run-up on shore •  Waves would decrease in size fairly rapidly from impact site

A hydrodynamic model of an ancient asteroid impact in the southern Pacific

Courtesy of Steven Ward, U California Santa Cruz

Adaptation to tsunami hazards

Buoys near the anticipated sources of tsunamis detect a tsunami in its early stages and transmit to the PTWC in Hawaii.

Adaptation to tsunami hazards

Tsunami warning systems give warnings of an hour to a day

Here is a map of the anticipated travel time for a tsunami originating in South America

Tsunami risks and adaptation to hazard

Tsunami hazard maps help communities with infrastructural adaptation and emergency planning

Infrastructure Tsunami hazard adaptation

Tsunami-resistant buildings Warning signs Vertical evacuation structures

Elevated restaurant in Hilo, Hawaii. Lower level is designed to allow waves to pass through.

How are we dealing with very rare but very consequential tsunami?

Three examples:

Japan, in preparation for the 2011 tsunami

Padang, West Sumatra

The South China Sea

The 869 deposits Possible 869 deposits No deposits

869 Simulation 2011 inundation

The 869 Jogan earthquake

49

A fault model proposed in 2008

Photo: Jose Borrero

Padang now (~800,000 people)

Padang in 1797 (~4,000 people)

A recent effort by German colleagues to estimate tsunami inundation for an earthquake I forecast in 2008

I minute

4 minutes

7 minutes

10 minutes

after arrival at coast Tools needed to do

this: Hydrodynamics, a sub-discipline of physics that is mathematically rigourous

A recent effort by German colleagues

Proposed vertical evacuation structure for Padang, Sumatra

During normal times, the structure would serve as a community recreational area

During a tsunami, people could run up to the park and escape the tsunami.

For more info go to http://geohaz.org/projects/sumatra.html

Clicker session

Hypothetical tsunami in the South China Sea

If the 1000-km long megathrust between Manila and Taiwan ruptures suddenly, this is a plausible pattern of tsunami wave heights. Note the focusing of highest waves on the southern coast of China, near Hong Kong and Macau

Hypothetical tsunami in the South China Sea

If the 1000-km long megathrust between Manila and Taiwan ruptures suddenly, this is a plausible pattern of tsunami wave heights. Note the focusing of highest waves on the southern coast of China, near Hong Kong and Macau

From Li Lin Lin, Earth Observatory of Singapore

8

6

4

2

0

10

met

ers

0

10 meters

Documents

Lecture 8 Tsunami