FIRTH
J. Javier Diez
1 and Efren M. Veiga
2
1
Research Group on Marine, Coastal and Port
Environment and Other Sensitive Areas, Department of
Land and Urban Planning and Environment, Universidad
Politécnica de Madrid, Madrid, Spain
2
Civil Engineering: Land & Urban Management and
Environment, Universidad Politécnica de Madrid, Escuela
de Caminos, Canales y Puertos, Madrid, Spain
Synonyms
Flooded glacial valley
Definition
The term firth is a modification of the more general
term fjord and is used to refer to the estuary formations
along Scotland’s eastern coast. Firths are shallower,
longer, and more heavily silted than fjords. They also act
as sediment traps for littoral drift and show evidence of
significant infilling (Firth et al., 1997). There are strong
analogies with the term bay used for other geographical
areas of glacial origins, such as along the northeast coast
of North America.
Genesis
Both the terms firth and fjord are generally applied to
water bodies resulting from the flooding of glacial valleys.
In general, intrusion of the sea into glacial valleys stems
from two factors: Quaternary eustasy and tectonic sinking
of grabens along the fractured plate margin borders. The
latter is greater on the western facade. Isostatic rebound
due to the present interglacial period seems to have had
a greater effect on firths. There is a conceptual symmetry
with the term ria, which also refers to coastal flooding
but of river valleys. Both kinds of estuaries have equivalent characteristics but different typologies (McManus
et al., 1993; Duck et al., 1995).
The flooded valleys of both firths and fjords are created
and carved out by glacial action, which produces their
depth and breadth; these features are also evident in
subaerial segments, even if the rivers that drain them are
subsequently able to rejuvenate the relief. Some show
a certain hydrological hierarchy of glacial origin that
endows the coast with its typical irregular morphological
and multi-lobed nature. In general, they receive river
flows at their heads. Some that formed more recently are
steeper, but they are always limited in length.
Glacial flows have a huge abrasive and erosive effect on
the sides and floors of valleys. Once the glaciers retreat, both
their moraine deposits and the valley’s abraded surfaces are
highly prone to weathering and erosion, which means that
the supply of sediment to the outlet can be enormous.
25
Lake of
Menteith
R.Forth
Stirling
Burntisland
30
35
65
70
Firth of Forth Drainage Basin
30
R.Avon
Grangemouth
30
0
1 5
35
15 kilometres
O c h i l H i l l s
Location
S o u th e rn
U p la n d s
H ig h la n d s
Edinburgh
P
e n t l a n d
H
i l l s
R
. E s k
G
a r i e t o n
H
i l l s
South
Queensferry
Forth
Bridges
L
o
m
o
n
d
H
i l l s
R. Le ve n
R .O re
Kincardine
Largo
Bay
Leven
Elie
North
Berwick
R .T y n e
Aborlady
Bay
C
l e i s h
H
i l l s
R. De vo n
R .C a rr o n
G a r g u n n o c k
H i l l s
A ll e n W a te r
R . T e it h
70
25
H
i g
h
l a
n
d
s
W a te r o f L e it
h
R .A lm
o n d
B a t h g a
t
e
H
i l l s
S o u t h e r n
U
p
l
a
n
d
s
F i r t h
o f
F o r t h
Firth, Figure 1 Firth of Forth Drainage Basin.
316
FIRTH
J. Javier Diez
1 and Efren M. Veiga
2
1
Research Group on Marine, Coastal and Port
Environment and Other Sensitive Areas, Department of
Land and Urban Planning and Environment, Universidad
Politécnica de Madrid, Madrid, Spain
2
Civil Engineering: Land & Urban Management and
Environment, Universidad Politécnica de Madrid, Escuela
de Caminos, Canales y Puertos, Madrid, Spain
Synonyms
Flooded glacial valley
Definition
The term firth is a modification of the more general
term fjord and is used to refer to the estuary formations
along Scotland’s eastern coast. Firths are shallower,
longer, and more heavily silted than fjords. They also act
as sediment traps for littoral drift and show evidence of
significant infilling (Firth et al., 1997). There are strong
analogies with the term bay used for other geographical
areas of glacial origins, such as along the northeast coast
of North America.
Genesis
Both the terms firth and fjord are generally applied to
water bodies resulting from the flooding of glacial valleys.
In general, intrusion of the sea into glacial valleys stems
from two factors: Quaternary eustasy and tectonic sinking
of grabens along the fractured plate margin borders. The
latter is greater on the western facade. Isostatic rebound
due to the present interglacial period seems to have had
a greater effect on firths. There is a conceptual symmetry
with the term ria, which also refers to coastal flooding
but of river valleys. Both kinds of estuaries have equivalent characteristics but different typologies (McManus
et al., 1993; Duck et al., 1995).
The flooded valleys of both firths and fjords are created
and carved out by glacial action, which produces their
depth and breadth; these features are also evident in
subaerial segments, even if the rivers that drain them are
subsequently able to rejuvenate the relief. Some show
a certain hydrological hierarchy of glacial origin that
endows the coast with its typical irregular morphological
and multi-lobed nature. In general, they receive river
flows at their heads. Some that formed more recently are
steeper, but they are always limited in length.
Glacial flows have a huge abrasive and erosive effect on
the sides and floors of valleys. Once the glaciers retreat, both
their moraine deposits and the valley’s abraded surfaces are
highly prone to weathering and erosion, which means that
the supply of sediment to the outlet can be enormous.
25
Lake of
Menteith
R.Forth
Stirling
Burntisland
30
35
65
70
Firth of Forth Drainage Basin
30
R.Avon
Grangemouth
30
0
1 5
35
15 kilometres
O c h i l H i l l s
Location
S o u th e rn
U p la n d s
H ig h la n d s
Edinburgh
P
e n t l a n d
H
i l l s
R
. E s k
G
a r i e t o n
H
i l l s
South
Queensferry
Forth
Bridges
L
o
m
o
n
d
H
i l l s
R. Le ve n
R .O re
Kincardine
Largo
Bay
Leven
Elie
North
Berwick
R .T y n e
Aborlady
Bay
C
l e i s h
H
i l l s
R. De vo n
R .C a rr o n
G a r g u n n o c k
H i l l s
A ll e n W a te r
R . T e it h
70
25
H
i g
h
l a
n
d
s
W a te r o f L e it
h
R .A lm
o n d
B a t h g a
t
e
H
i l l s
S o u t h e r n
U
p
l
a
n
d
s
F i r t h
o f
F o r t h
Firth, Figure 1 Firth of Forth Drainage Basin.
316
FIRTH