World Record Tsunami
"What is a tsunami...?
And I don't see a huge wave in the picture, anywhere."
Well, a tsunami (it's actually a Japanese word) is a word scientists
use to describe an enormous wave (or series of waves) that happens
when an large amount of energy is released into the waters of the
ocean - creating a ripple effect. The effect is similar to what you'd
see when you drop something heavy in the bathtub, or throw a rock
into a lake. In the case of a tsunami, the the "ripples" in the water
can come from:
1) an earthquake (movement of the sea floor)
2) a volcanic eruption (lava and rock going "kersploosh" into the
sea)
3) a huge landslide, as was the case in Lituya Bay
The incredibly
massive size of the material 'plopping' into the ocean (or the shifting
of the sea floor) creates MAJOR ripples that are so big they are gigantic
waves traveling at speeds of up to 300km/h over really long distances
in the open sea. But, when the waves reach the beach they are incredibly
high and wash way inland causing major damage and sometimes
loss of life.
You're
asking, "why no wave in the picture?" Well, close
up shots of tsunamis actually happening
are pretty rare and hard to get, as you can imagine. Would YOU stand
on the shore with a camera to take a picture of a ten-story high wave
coming right at you? Most people turn and run for the hills because
their lives are in serious danger.
Enormous Earthquake
Lituya Bay
is a large inlet along the coast of Alaska that is in a seismically
active area - part of the "Pacific Rim of Fire". What happened
at Lituya was movement along the fault that runs from left to right
in the above picture. If you pretend you're actually standing on the
ridgetop looking out over the Bay (like the view in the above picture)
the fault would be in the mountains behind you. The "movement in the
fault", of course, is called an earthquake. The magnitude of the quake
was about 8.3, although some
This photo shows the damage to the headland;
every living thing was completely wiped off where the first major
wave struck. |
sources say
it was a 7.9, on the Richter Scale
(a scale for measuring the magnitude, or amount of energy released,
from an earthquake). Pretty awesome shaker. Well, shaker it was...it
"shook" loose an estimated 40 million cubic yards of dirt and glacier
from a mountainside at the head of the Bay, about where you're standing
in the above picture. When the stuff went "kersploosh" into the water
it created a massive wave that washed 500m high over the headland
in the right side of the above picture. The tsunami inundated approximately
5 square miles of land along the shores of Lityua Bay, sending water
as far as 3,600 feet inland, and clearing millions of trees.You can
see the damage to the trees that were growing on the headland when
the wave washed over the top of it - there were no trees left...wiped
'em clean off. The picture above gives you a closer view of the damage
to the headland that the tsunamil waves caused.
Human Witnesses
There were
three fishing boats anchored at the mouth of Lituya Bay on the day
the awesome waves
U.S.G.S. Aerial photo of Lituya Bay taken after July 9, 1958
event. Note the extent of the non-forested areas of land lining
the shore of the bay, which marks the approximate reach of the
tsunami's runup. |
happened.
That's the main reason we know it happened. There were human witnesses
to the catastrophic event. Unfortunately, one of the boats was close
to shore and the huge waves overtook it killing the two people on
board. Amazingly, the other two boats "rode" the tidal waves as they
washed from the source of the landslide and resonated around the bay,
like water sloshing in a wash basin. The boaters watched in horror
as the first enormous wave engulfed the small fishing boat and wiped
everything in its path off the land. If there had been a town or city
on the shores of the bay everyone in it would have been killed. Fortunately,
because it was an unpopulated area, the loss of life was minimal (although,
the family of the victims hardly think that it was good fortune).
How Do They
Know?
To measure
the height of the biggest wave, all scientists had to do was look
for the high water mark
- that's the line where the water reached its highest point on
the nearby land. It's real easy to find you just look for the uppermost
edge of the damaged area (see photo at left).
Then, they
measured the elevation of the highest point on the high water mark
to get a measurement of 500m high - the biggest wave ever measured.
Other Big Waves
There are
waves out on the ocean all the time, which are created by the friction,
or the dragging motion, of
The yellow mark illustrates the maximum height
the wave reached as it washed over the headland. |
the wind
over the vast surface of the sea. When big storms develop out at sea
creating fast winds it causes really big waves, called storm
waves. Ships out at sea during
these really big storms have experienced some pretty big waves, some
as much as 30m high, but that's about as big as storm waves get out
on the open sea. Nothing like the "big one" at Lituya Bay
Here's something
to think about...There happened to be people fishing in the Bay the
day that the landslide and resulting tidal wave occurred. That part
of Alaska is not populated, but people come to that area for many
reasons. There are places on this earth that are so inhospitable
(really bad) that few people ever visit. For example, the Arctic,
or the Antarctic, in winter are some pretty nasty, cold places. Not
only are they not fun places to visit, but they're virtually inaccessible
to humans in winter. It's totally possible that in early spring, when
the ice starts to melt, and glaciers calve
into the ocean (break off HUGE chunks) that really big waves occur.
Possibly even bigger than the massive one at Lituya Bay! The wave
may wash up over ice and ice-covered land, but the evidence melts
away so that no human ever knows it happened.
We say that the tsunami at
Lituya Bay was the biggest wave ever, but that's just the ones humans
have witnessed and have been able to record. There have probably been
even BIGGER waves that have happened in the past when human witnesses
didn't even exist. And you never know, there may even be a bigger
wave to happen yet!
