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Interior Bottomlands

↑About the Interior Bottomlands

The Interior Bottomlands consist of five discontinuous sections of varying sizes, separated by areas of higher elevation, located in interior Alaska. This region, most of which is unglaciated, features meandering, slow-moving rivers and a mosaic of forests and open wetlands. It is also home to Fairbanks, the largest city in Alaska's interior.

The climate is subarctic and continental throughout most of the region, although there is a small area in the east of this region around Fairbanks that is significantly warmer in summer, and is usually classified towards the cold end of a humid continental climate. Precipitation tends to increase to the west. Due to the cold temperatures, most of the precipitation falls in summer, but there is some snowfall in winter. Daily weather is unpredictable and variable, with large temperature swings possible. Because solar radiation is minimal in winter, winter warmth primarily arrives in the form of humid air blown off the ocean; this air is mostly blocked by the Alaska Range to the south, but some such warm air still reaches this region.

Parts of this region, especially where it is surrounded by hills or mountains, experience frequent temperature inversions in which cold air at the surface is blocked by a layer of warm air above. These inversions can interact with cold air drainage from higher elevations, such that this region can be significantly colder than in surrounding higher-elevation regions, at least on some days. Conditions early in the growing season can be dry enough to cause significant drought stress, leading to relatively regular wildfire. As with cold air, wildfire smoke can often accumulate in this region.

The terrain mostly ranges from flat to nearly so, although there are a few small areas of hills. Although most of this area was not recently glaciated, there are some areas of glacial outwash or moraines from glaciers in adjacent areas. Throughout the rest of the region, the surface soils were either deposited by rivers or wind; bedrock is deeply buried by these deposits in most places. There is discontinuous permafrost throughout, which, combined with the flat topography, contributes to poor drainage and surface soils with a high portion of organic matter. Soil pH varies extremely wildly, reaching as low as 2 on some sites, but being alkaline (above 7) on some soils deposited along major rivers. There are numerous slow-moving, meandering streams throughout, and some larger rivers. Most wetlands formed either as oxbow lakes as streams changed course, or thaw ponds formed from melting permafrost. These thaw ponds are dense in areas. Near the southern border of this region with the Alaska Range there are also a few lakes of glacial origin formed where moraines from glaciers in the mountains blocked the drainage. Some areas with gravely soils have groundwater-fueled seeps and springs; contrasting with regions farther south, this region has some groundwater-fed wetlands with highly acidic water, where the groundwater is steeped in organic matter and separated from underlying mineral soils by permafrost.

This is the most populous region of interior Alaska, both because settlements tend to be located along rivers, and the climate here is milder than at higher elevations, but the population is almost exclusively located in the easternmost portion of this region. The largest city here is Fairbanks, which is mostly located inside this region although a portion of its metro area extends outside it into the Interior Forested Lowlands and Uplands. North Pole and Delta Junction are the next-two-largest settlements here. The other portions of this region are sparsely populated, with the largest settlement being Grayling, with under 200 people. Land use here includes mining of gold and silver, and, particularly in the warmest parts of this region logging and agriculture. There is both subsistence and recreational hunting and fishing throughout.

This region has the lushest forest cover of anywhere in interior Alaska, and generally supports forests except on sites where the cover is disrupted by poor drainage and/or permafrost, which is more likely to occur in the lowest areas. Better-drained sites support forest of mostly spruce, with various hardwoods, interrupted by frequent wetlands with thickets of tall scrub. Areas along major rivers are dominated by white spruce (Picea glauca) and balsam poplar (Populus balsamifera). Warmer, south-facing slopes support white spruce, birch, and quaking aspen (Populus tremuloides). Floodplains and river bars support alders and willows. There are also sedge meadows and various aquatic vegetation in oxbow lakes and other wetlands along the rivers. Low, flat areas with more permafrost support black spruce (Picea mariana) woodlands where able, and stunted growth of birch and ericaceous shrubs and sedge-tussock bogs where trees cannot grow.

This region is almost entirely surrounded by the Interior Forested Lowlands and Uplands, a similar region that is slightly higher in elevation, better-drained, and slightly more rugged. In the far east of this region, there is an area where it directly borders the Interior Highlands and Klondike Plateau, a region that is significantly higher and more rugged. Both of these regions, like this one, straddle the border of where trees and forests are able to survive. In the far west, there is a small area where this region directly borders the Subarctic Coastal Plains, a low, flat, coastal area of tundra, generally devoid of tree cover. In that area there is also a small border to the south with the Ahklun and Kilbuck Mountains, a low but steep mountain range with pronounced glacial features.