How does the Ob River’s northward flow contribute to widespread flooding?

The Ob River’s northward flow is a significant factor in its tendency to flood because the river’s upstream sections thaw earlier than its downstream reaches.12

As spring arrives, the southern, upstream portions of the river begin to melt, releasing water and ice that flow toward the north. Because the lower reaches near the Arctic remain frozen for a longer period, this moving water and ice encounter a solid, intact ice cover. This obstruction often causes the formation of ice jams, which prevent the river from draining effectively and force water levels to rise significantly, leading to widespread flooding.12

This phenomenon is characteristic of northerly flowing rivers, where the downstream ice acts as a barrier to the earlier-thawing upstream flow. These spring breakup jams are particularly destructive, often resulting in flooding that can last for months in the lower reaches of the river.21