Kodiak-Shelikof Subregion

The land surface of the Kodiak-Shelikof subregion is steep, rugged, and extensively glaciated. Exposed bedrock covers 50 to 60 percent of the area (Figure 53a), and erosion potential is high primarily due to excessive slope and erodable ash soils. Glacial till covers lower mountain slopes, benchlands, and valleys and is overlain by volcanic ash on lower slopes and along drainages. These middle and lower slopes support well-drained silty and fine sandy-ash soils developed on weathered bedrock, glacial till, or gravelly outwash deposits. Valley bottom soils are shallow, well to poorly drained loams. These soils are usually rich in volcanic ash which has been transported from upper mountain slopes, and they generally overlie sandy and gravelly outwash materials. A narrow belt of shallow, gravelly, well-drained soils borders the steep, eastern slopes of the Aleutian Range. The location and distribution of these soil types are shown in Figure 125a.

All of the subregion is in the maritime climatic zone and experiences long, cool summers and short, cool winters. Moderate to large amounts of rainfall support a fairly heavy annual growth of vegetation in soils that are typically rocky, organic, or volcanic. These soils support tall brush, grass, and some moist tundra at higher elevations and coastal spruce on lower slopes. Limitations on types of vegetation are due not only to soil types but also to land slopes. Soil slips are common on upper slopes. Within the subregion, agricultural use of the soils is limited. Not only is such acreage scarce, but the subregion as a whole lacks the periods of warmth demanded by most crops. Typically, Kodiak averages only five days per year when temperatures exceed 70 degrees F. Garden crops can be grown on a small scale at many locations. Minor investigations involving fertilized native and introduced grasses indicate that small grains can be successfully raised to the forage stage. However, native grasses are more reliable and equally productive. The area contains extensive productive grasslands well adapted to grazing for periods ranging from eight months on Kodiak Island to year-round at points further south.

Cook Inlet Subregion

The lowland areas of the Cook Inlet subregion are mantled with glacial deposits that range widely in texture and are overlain by well to poorly drained silt loams. Peat soils occupy depressions making up 30 percent of the lowland areas. Gravelly till and outwash are overlain by shallow to moderately deep silty soils throughout the Kenai and Susitna lowlands and on adjoining mountain slopes. Windblown silt covers uplands throughout the area (Figure 53b).

The subregion's steep upper slopes have shallow, gravelly and loamy deposits with many bedrock exposures. Well-drained, dark, gravelly to loamy soils occupy steep upper slopes and ridges along the south flank of the Alaska Range and throughout upper slopes of the Chugach and Talkeetna Mountains. Poorly drained, gravelly and stony loams with permafrost occupy north-facing slopes of foothills, moraines, and valley bottoms in this area. Silty soils on the east slopes of the Alaska Range and the west flanks of the Kenai Mountains along lower Cook Inlet are well-drained and have no permafrost.

Stream bank and coastal erosion is active throughout the subregion. Potential water erosion is moderate on low slopes and severe on steeper slopes. Wind erosion is active on uplands adjacent to the Matanuska and Knik Rivers.

The majority of the Cook Inlet lowlands falls within the transitional climate zone and progressively less ocean moderation affects the climate towards the inland areas. Precipitation, temperatures, and the length of the frost-free period have direct bearing on the soils and their productivity. Vegetation above tree line in the steep, rocky soils is predominantly alpine tundra, while the well-drained upland soils support white spruce. Boreal forests dominate northern portions of the subregion with inclusions of high brush along slopes of the Talkeetna Mountains and the Alaska Range. Well-drained gravelly soils on the lower slopes of the Alaska Range and on the south and west slopes of the Talkeetna Mountains support grassy range land, while poorly drained soils on valley bottoms support muskeg-bog. Tideflats are dominated by sedge meadows where drainage is poor. They are bordered by moist tundra grading into lowland spruce-hardwood forests in well-drained loamy soils.

Most agricultural activity in the state, from crop farming to dairy farming, occurs in this subregion. The most recent survey indicates that 2.55 million acres of land have soil characteristics conducive to the production of cultivated crops in the Cook Inlet-Susitna Lowlands up to elevations of 1,500 feet. Approximately 30 percent is located on the west side of the Kenai Peninsula; the balance is in the valleys of the Matanuska and Susitna Rivers and their tributaries, with a small portion near the lower Beluga River. The soils are characteristically well-drained, strongly acid, loamy materials with local areas of poorly drained peat.

Copper River-Gulf of Alaska Subregion

Types and distribution of soils in the Copper River-Gulf of Alaska subregion are fairly complex (Figure 125c). Soils of the coastal plain are poorly drained, stratified, clayey and silty sediments associated with peat in low tidal areas and stratified sands and silts having good drainage characteristics in the broad river delta deposits. The dominant soil in the Chitina valley is a well-drained, shallow silt loam overlying gravelly materials on moraines and terraces. Associated with these soils are well-drained stony and gravelly soils on lower slopes, and wet soils with permafrost in depressions. Recent moraines bordering glacial fronts consist of stony to very gravelly till. Older moraines and mountain foot slopes are covered by well-drained gravelly to loamy acid soils associated with peat. The Gulkana basin is characterized by poorly drained, deep, clayey soils having a thick organic mat and permafrost, surrounded by wet silty to loamy soils on valley side slopes and low moraines. Well-drained, shallow, acid, gravelly to loamy soils with deep permafrost occupy high moraines in the uplands. Poorly drained soils with a thick organic mat and permafrost occupy upland depressions. Steep upper slopes and high valleys in the Chugach Range and Wrangell Mountains are occupied by well-drained, shallow, stony and gravelly soils.

Erosion potential is moderate on finer sediments of low slopes and low on river sands and gravels. The gravelly to loamy soils associated with mountain foot slopes and older moraines have a high erosion potential.

Climate of the Copper River valley is severe with long, cold winters and short, hot summer seasons. Precipitation varies from small amounts in the basin to moderate amounts in the surrounding mountains to heavy rainfall on the coast. Existing vegetation is regulated not only by climatic factors, but also by soil types, drainage, and slopes. The well-drained to poorly drained gravelly soils along the coasts of the mainland and the numerous islands of Prince William Sound are dominated by Sitka spruce and western hemlock forests. The poorly drained clayey soils of the basin support the lowland spruce type, while the poorly drained loamy soils surrounding the basin support an upland spruce forest type. The major river valleys contain a bottomland spruce type growing in well-drained gravelly or loamy soils. On the southern flanks of the Alaska Range wet, peaty, loamy soils support moist tundra. Alpine tundra is characteristic of steeper slopes and rocky soils at higher elevations.

Agricultural activities in the subregion are limited by climatic factors. Spring and summer temperatures are relatively high, and early vegetative growth is rapid. However, the proximity of very high mountains and downward flows of cold air combine to make the area susceptible to summer frosts and limit reliable agricultural production to gardens and forage crops.

Generally, the lowlands have relatively little range forage value. However, following fire, invading grasses, forbs, and deciduous perennials may produce considerable forage. Available moisture will generally set the upper limit of productivity. Above the brush zone and timberline lies a narrow, grassy tundra strip which has high grazing value for either domestic or wild animals. Range resources of the subregion are mainly along the Copper and Chitina river valleys. Narrow coastal strips and stream deltas along the coast might be grazed during summer, but the animals would have to be removed for the balance of the year.

Back to Index

[Alaskool Home]