CHAPTER 6 . The Argentina Estuaries: A Review
127
Perillo et al. (1996) found on the marsh a large number of salt pans with their long
axis mostly oriented parallel to the main wind direction. They were able to discover a
mechanism of tidal channel formation by the interconnection of these pans. This is a
remarkable finding since it is normally regarded that salt marsh channels are inherited features from the tidal flats previous to their colonization by plants.
Further geomorphologic studies have been concentrated on the northern shore of
the estuary, where the evolution of gravel spit were analysed within historical times
by comparing maps and aerial photographs. Melo et al. (1998) discussed the effect of
wind, tidal currents but specially the waves formed along the estuary water body as
the most important agents in the evolution of the spits and cliff recession.
6.6
Tierra del Fuego Estuaries
In Tierra del Fuego island exists numerous but small estuaries. The more significant
are the estuaries of Grande and Carmen Sylva Rivers which are of the coastal plain
type. San Sebastian Bay has the typical characteristics of a restricted coastal lagoon
because of the large spit that partly close its mouth and the influence of the San Martin
River that discharge into the bay. In fact the San Martin River itself is a coastal plain
inner estuary. Several studies have been done in the bay, but unfortunately to the authors knowledge little is known about the rest of the Tierra del Fuego estuaries.
Along the Mitre Peninsula (the tip of Tierra del Fuego) there are several small rivers that develop ria type estuaries. They are from north to south Ewan or Brazo Norte,
San Pablo, Lainez, Irigoyen, Noguera, and Bueno. Few estuaries also flow to the Beagle
Channel, these are Bompland, Lopez and Moat Rivers. Most of these estuaries are located in such a remote area that there are no roads allowing for adequate transport of
equipment to study them. Also, the Strait of Lemaire, between Mitre Peninsula and
the los Estados Island is very dangerous navigation passage for the small boats needed
to study these estuaries.
6.6.1
San Sebastian Bay
San Sebastian is a wide bay located in northern Tierra del Fuego having a semicircular shape partly closed by a long and narrow gravel spit. The bay is 55 km in length
and 40 km wide (Fig. 6.16). The spit has a length of 17 km with width varying between
50 and 1000 m (at the tip). The open mouth is about 20 km wide. Freshwater input
into the system is provided by the San Martin River (there is no gauging of river discharge) at the southwestern part of the bay. Tidal range is 10 m and wind influence is
from the west with the same characteristics described by Rio Gallegos. Perillo (1995)
suggested that the bay can be considered as a restricted coastal lagoon.
Wave action in the bay is two fold. The oceanic waves enter into the bay through
the moutlI and attack the southern coast up to the mouth of the river and along the
outer face of the spit. Locally generated wave have the fetch of the bay and move seaward or towards the inner face of the spit. The spit also controls the circulation of the
tidal currents. Basically the flood currents enter along the southern border of the
mouth and circulate clockwise along the bay and inner face of the spit, ebbing on the
127
Perillo et al. (1996) found on the marsh a large number of salt pans with their long
axis mostly oriented parallel to the main wind direction. They were able to discover a
mechanism of tidal channel formation by the interconnection of these pans. This is a
remarkable finding since it is normally regarded that salt marsh channels are inherited features from the tidal flats previous to their colonization by plants.
Further geomorphologic studies have been concentrated on the northern shore of
the estuary, where the evolution of gravel spit were analysed within historical times
by comparing maps and aerial photographs. Melo et al. (1998) discussed the effect of
wind, tidal currents but specially the waves formed along the estuary water body as
the most important agents in the evolution of the spits and cliff recession.
6.6
Tierra del Fuego Estuaries
In Tierra del Fuego island exists numerous but small estuaries. The more significant
are the estuaries of Grande and Carmen Sylva Rivers which are of the coastal plain
type. San Sebastian Bay has the typical characteristics of a restricted coastal lagoon
because of the large spit that partly close its mouth and the influence of the San Martin
River that discharge into the bay. In fact the San Martin River itself is a coastal plain
inner estuary. Several studies have been done in the bay, but unfortunately to the authors knowledge little is known about the rest of the Tierra del Fuego estuaries.
Along the Mitre Peninsula (the tip of Tierra del Fuego) there are several small rivers that develop ria type estuaries. They are from north to south Ewan or Brazo Norte,
San Pablo, Lainez, Irigoyen, Noguera, and Bueno. Few estuaries also flow to the Beagle
Channel, these are Bompland, Lopez and Moat Rivers. Most of these estuaries are located in such a remote area that there are no roads allowing for adequate transport of
equipment to study them. Also, the Strait of Lemaire, between Mitre Peninsula and
the los Estados Island is very dangerous navigation passage for the small boats needed
to study these estuaries.
6.6.1
San Sebastian Bay
San Sebastian is a wide bay located in northern Tierra del Fuego having a semicircular shape partly closed by a long and narrow gravel spit. The bay is 55 km in length
and 40 km wide (Fig. 6.16). The spit has a length of 17 km with width varying between
50 and 1000 m (at the tip). The open mouth is about 20 km wide. Freshwater input
into the system is provided by the San Martin River (there is no gauging of river discharge) at the southwestern part of the bay. Tidal range is 10 m and wind influence is
from the west with the same characteristics described by Rio Gallegos. Perillo (1995)
suggested that the bay can be considered as a restricted coastal lagoon.
Wave action in the bay is two fold. The oceanic waves enter into the bay through
the moutlI and attack the southern coast up to the mouth of the river and along the
outer face of the spit. Locally generated wave have the fetch of the bay and move seaward or towards the inner face of the spit. The spit also controls the circulation of the
tidal currents. Basically the flood currents enter along the southern border of the
mouth and circulate clockwise along the bay and inner face of the spit, ebbing on the