Geoscience Reference
In-Depth Information
4
Coastal Landscape Evolution
4.1
Introduction
Inquisition. Immanuel Kant and Jean-Jacques Rousseau
viewed the disaster as a natural event and emphasized the
need to avoid building in hazardous places. The Lisbon
earthquake also gave birth to scientific study of geological
events. In 1760, John Mitchell, geology professor at Cam-
bridge University, documented the spatial effects of the
earthquake on lake levels throughout Europe (Mitchell
1760
). He found seiching along the coastline of the North
Sea and in Norwegian fjords, Scottish lochs, Swiss Alpine
lakes, and rivers and canals in western Germany and the
Netherlands. He deduced that there must have been a pro-
gressive, wave-like tilting of the Earth outwards from the
center of the earthquake and that this was different from the
type of wave produced by a volcanic explosion.
Mitchell's work in 1760 on the Lisbon earthquake
effectively represented the separation of two completely
different philosophies for viewing the physical behavior of
the natural world (Bryant
2005
). Beforehand, the catastro-
phists—people who believed that the shape of the Earth's
surface, the stratigraphic breaks evidenced in rock columns,
and the large events that were associated with observable
processes were cataclysmic—dominated geological meth-
odology. More importantly, these catastrophic processes
were Acts of God. The events had to be cataclysmic in order
to fit the many observable sequences observed in the rock
record into an age for the Earth of 4004 BC, determined
from Biblical genealogy. Charles Lyell, one of the fathers of
geology, sought to replace this catastrophe theory with
gradualism—the idea that geological and geomorphic fea-
tures were the result of cumulative slow change by natural
processes operating at relatively constant rates. This idea
implied that processes that shape the Earth's surface fol-
lowed laws of nature defined by physicists and mathema-
ticians. Whewell, in a review of Lyell's work, coined the
term uniformitarianism, and subsequently a protracted
debate broke out on whether or not the slow processes we
observe at present apply to past unobservable events. To
add to the debate, the phrase ''The present is the key to the
past'' was also coined.
Large earthquakes on the sea floor, submarine slides, and
asteroid impacts with the ocean can create tsunami waves
that spread ocean-wide with profound effects on coastal
landscapes. They can generate run-up heights 30 times
greater than their open ocean wave height and sweep sev-
eral kilometers inland. This penetration inland can only be
duplicated on flat coastlines by storms if they are accom-
panied by a significant storm surge. Tsunami are thus cat-
astrophic events and can leave a permanent imprint on the
landscape. There has been little appreciation in the literature
that coastal landscapes may reflect tsunami processes rather
than those induced by wind-generated waves and wind.
Catastrophic events—termed catastrophism—are not well
respected in modern science. This chapter will describe the
role of catastrophism in the development of modern geo-
logical thinking, show in more detail how tsunami are dif-
ferent from storms, describe various models of tsunami-
generated
landscapes,
and
illustrate
these
models
with
examples from around the world.
4.2
Catastrophism Versus
Uniformitarianism
A tsunami was involved in one of the pivotal debates of
modern scientific development (Huggett
1997
). On
November 1, 1755, an earthquake with a possible surface
wave magnitude, M
s
, of 9.0 destroyed Lisbon, then a major
center of European civilization. Shortly after the earthquake
a tsunami swept into the city, and over the next few days
fire consumed what was left of Lisbon. The event sent shock
waves through the salons of Europe at the beginning of the
Enlightenment. The earthquake struck on All Saints' Day,
when many Christian believers were praying in church.
John Wesley viewed the Lisbon earthquake as God's pun-
ishment for the licentious behavior of believers in Lisbon,
and
retribution
for
the
severity
of
the
Portuguese
