Riverbank Layers
Read the story of climate change in riverbank layers.
Imagine you can see a fast-moving stream in front of this sign. The swiftly flowing water on the outside of the bend has eroded the far bank, exposing layers of sediment and fossil remains. Some layers were laid down during cold, dry full glacial periods. Others were deposited during interglacial periods when the climate was as mild, or milder, than today. Look for these layers in the stream bank.
Bedrock - solid rock below the soils and till. In areas that have been glaciated, bedrock is often smoothed and rounded. This bedrock was rounded, but a piece froze to the base of the glacier and was sheared off as the glacier moved, leaving a rough surface.
Till - rounded rocks mixed with sand and clay. Till was left behind by glaciers.
Paleosol - prehistoric soils formed from decomposed plant matter. They developed most completely during the warmer interglacial periods.
Loess - light-coloured, mineral-rich particles blown off streambeds left by retreating glaciers. The thickness of this layer depends on its nearness to the source and the winds that blew when it was deposited. Winds are stronger during colder periods.
Campfires - small pockets of charcoal about 45 cm (18 inches) across. They often contain bones.
Tephras - layers of volcanic ash. Because they extend over large areas and are easy to recognize and date, tephras are used as markers to compare events in different locations. The tephra above the paleosol is the Dawson Tephra, which is about 24,000 years old. The lower tephra is older.
Streambed - bones collected in the streambed after being washed down into the water channel.
Soil - this layer has been developing since the peak of the last glaciation.
Organic matter lies near the surface, and a weathered mineral layer (horizon)
lies below it. The amount of soil development is directly tied with the region's
climate. This modern soil is relatively thin, reflecting the arid subarctic
climate of the Yukon.
What do you think the layer being deposited now will look like in 10,000
years?