Landforms of British Columbia 1976 - Department of Geography

NASS BASIN
The Nass Basin (see Plate XXB) is an irregularly shaped area of low relief, for
the most part lying below 2,500 feet elevation, which is drained by the Nass River
and its tributaries and by the Kitwanga and Kispiox Rivers, tributaries of the Skeena.
The basin extends from the junction of Teigen Creek with the Bell-Irving River
southeastward for 130 miles to the Skeena River at Hazelton. The maximum width
of the basin, northeasterly at Swan Lake, is about 25 miles.
,The basin is encircled by mountains, the Boundary Ranges on the west, the
Hazelton Mountains on the south, and the Skeena Mountains on the east. The moun-
tains rise abruptly from the gently rolling floor of the basin, as is displayed strikingly
on N.T.S. Sheet 103~. A prominent northeasterly trending lineament lies along the
southeastern margin of the basin (see Plate XXIA) . Rocks underlying the basin are
dominantly volcanic members of the Hazelton Group.
The basin is flat or gently rolling, rising gradually to 5,148 feet at Mount Bell-
Irving and 4,000 feet at several other points. Meziadin Lake (806 feet) and Bowser
Lake (1,027 feet) lie on the western side of the basin. The floor of the basin is
dotted with hundreds of small lakes which, together with the drainage pattern, dis-
play a well-developed southeasterly trend that swings to southwesterly below Cotton-
wood Island on the Nass River. The basin was occupied by glacial ice, and the
numerous lake basins of glacial origin and many of the stream courses are parallel
to drumlin-like forms developed by ice movement.
Ice from the Boundary Ranges and the Skeena Mountains poured down the
Bell-Irving River into the Nass Basin and escaped by Kispiox Valley and Kitwanga
Valley into the Skeena, also by way of the Nass River valley southwestward to the
sea beyond Aiyansh. Some moved through the gap past Lava Lake, and some pressed
over the mountains and down Cedar River to escape by way of Kitsumkalum Lake
valley to Kitimat Valley. The strongly developed lineation displayed by drift forms
and sculptured rock is an inheritance of the flow of Pleistocene ice (see Plate XXIA) .
A feature of very great interest is the outpouring of Recent lava from a vent at
the head of Tseax River. The vent is 3% miles east of the north end of Lava Lake
on the Columbia Cellulose road north of Terrace, Lava flowed down the tributary
to the main valley of Tseax River, damming it and creating Lava Lake. The lava
from there flowed northward for almost 12 miles to the Nass River, being confined
for part of the distance within the narrow valley of Tseax River. On reaching the
Nass Valley the lava spread out and formed an almost flat lava plain about 7 miles
long and 3 miles wide along the south side of the Nass River (see Plate XLVIIB) .
The northern margin of the flow constricts the Nass Valley for several miles below
Aiyansh and rises in cliffs along the south side of the river.
The precise age of the lava eruption is not known, but is thought to be not
greater than 300 years. Vegetation has only begun to encroach upon the lava, and
there has been little or no erosion of the lava. The surface retains its original charac-
teristics, marked by irregular fragments of flow breccia, ropy lava surfaces, and
collapse features where the upper crust has broken into subsurface caverns.
This remarkable feature is readily accessible by road north of Terrace.
[References: “ Stikine River Area,” Geol. Surv., Canada, Map g-1957; N.T.S.
Sheets 93M, 103~, and ~&IA.]
[Photographs: B.C. 468:87; B.C. 505:74, 102; B.C. 508:5, 20, 33, 76;
B.C. 541: 34.1
HAZELTON MOUNTAINS
The Hazelton Mountains lie east of the Kitimat Ranges of the Coast Mountains
and extend southeastward from the Nass River and Nass Basin for about 150 miles
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