In my new book, Improbable Planet, I list and describe 11 different reasons why a human civilization sustaining billions of humans would be impossible if it were not for our living at the end of a highly fine-tuned ice age cycle. Now, a scientific research team has discovered a twelfth reason.1 An especially strong ice age cycle, like the one we are in now, generates many large gravel-bed river floodplains, which prove to be ecological bonanzas.
An ice age cycle is an ice age where the amount of ice coverage on Earth’s surface cycles between about 10 percent and 15–25 percent. Such a cycle has been in effect for only the last 0.00057 part of Earth’s history. It came about as a result of the sun reaching the midpoint of its burning history and five simultaneous very rare and very dramatic tectonic events. I describe these extraordinary circumstances in my book Improbable Planet.2 However, until just 800,000 years ago, the ice age cycle’s period was too brief to produce the benefits required for a global human civilization. Furthermore, only the last deep ice age in the cycle yielded all the benefits necessary for global human civilization to be possible. We are living in the only interglacial period in the ice age cycle—and for that matter, in the entire history of the earth—during which billions of humans could receive God’s gift of redemption!
We should thank God for the ice age cycle because such a cycle produces many long-lasting gravel-bed river floodplains. Such floodplains only occur in glaciated mountain landscapes. Melting glaciers, especially valley glaciers, in mountain ravines and canyons result in water, rocks, gravel, and silt spreading out in valleys below the mountains. Such landscapes are characterized by four highly differentiated seasons. These seasonal differences produce “dynamic fluvial processes that constantly change and renew the surface and subsurface of the river’s valley floor.”3
The featured image for this blog shows a photo I took of a gravel-bed river floodplain in southern British Columbia. This floodplain was generated by the melting of North America’s southernmost ice field, the Conrad Icefield in Bugaboo Provincial Park. The waters of this floodplain constitute one of the sources of the Columbia River.
For the first time, an interdisciplinary research team—that involved hydrologists, avian ecologists, fresh water biologists, and large mammal ecologists—worked together both to study the geological and ecological dynamics of gravel-bed river floodplains and to take an inventory of all the benefits such floodplains bring. They found that these floodplains support an unexpectedly high number of species. Specifically, they determined these floodplains are “focal points for biodiversity in maintaining viable aquatic, avian, and terrestrial populations.”4
The following is a list of the unique benefits accruing from gravel-bed river floodplains that the research team has discovered to date:
- The floodplains provide a unique habitat that sustains a much larger number of aquatic, avian, and terrestrial species than the surrounding regions.
- They serve as a connectivity zone linking the surrounding habitats and the species they contain.
- They efficiently recycle life-critical nutrients.
- The nutrient-rich waters below and lateral to the main water channels support a complex web of abundant microbes, insects, and crustaceans, which in turn sustain large populations of fish, amphibians, birds, and mammals.
- The downwelling water from the surface channels into the gravel beds below carries large amounts of dissolved and particulate organic material that sustains microbial decomposers that release biologically available nitrogen and phosphorus.
- The floodplains yield nutrient-rich resources that sustain aquatic insects and other invertebrates that inhabit the gravel beds from valley wall to valley wall of the floodplain, which provide a food chain base for fishes, amphibians, bats, birds, and both small and large mammals.
- The periodic flooding and groundwater-to-surface-water exchanges generate optimal spawning habitats for a wide variety of fish species.
- The trees that fall into the river and stream channels as a result of cut-and-fill alleviation events create shaded water pools that protect fish and other species from harmful summer heat.
- The combination of large-scale floods, cut-and-fill alleviation events, and wildfires create a highly productive, highly diverse vegetation community that sustains large-bodied mammal herbivores and large-bodied mammal carnivores.
- The compression of elevation differences within small areas establishes large moisture gradients that further enhance the diversity of plant species.
The team further noted that without floodplain habitats, many large-bodied mammal species—for example, moose, beaver, and river otters—would not survive. They also observed that top predators, such as wolves, critically depend upon gravel-bed river floodplains for their food. They estimated that 40 percent of all kills by wolves occur on gravel-bed river floodplains.
Image 1: Town of Field and the Trans-Canada Highway Disturb the Ecosystem of the Kicking Horse River Gravel-Bed Floodplain Ecosystem
Image credit: Hugh Ross
The team closed their research paper with an appeal. They pointed out that modern humans have undervalued the importance of gravel-bed river floodplains. The erecting of dams, towns, highways, and other structures in gravel-bed river floodplains (see image 1) greatly diminishes the ten benefits listed above. However, there would hardly be any gravel-bed river floodplains at all if it were not for our living in an ice age cycle with a periodicity of about 100,000 years (and where the last ice age in the cycle manifested the greatest extent of ice). As I explain in my book Improbable Planet, there would be no ice age cycle, let alone one that generates all the gravel-bed river floodplains that currently exist on Earth, if it were not for the simultaneous occurrence of five miraculous and unprecedented tectonic events that are timed at the just-right point in the sun’s nuclear burning history.5
Thank God for the ice age cycle! Thank God for our living at the just-right time in the ice age cycle that we are blessed with so many large, nutrient and ecologically rich gravel-bed river floodplains.
- F. Richard Hauer et al., “Gravel-Bed River Floodplains Are the Ecological Nexus of Glaciated Mountain Landscapes,” Science Advances 2 (June 2016): e1600026, doi:10.1126/sciadv.1600026.
- Hugh Ross, “Ready for Occupancy,” chap. 15 in Improbable Planet (Grand Rapids: Baker, 2016).
- Hauer et al., “Gravel-Bed,” 1.
- Ross, “Ready for Occupancy,” chap. 15 in Improbable Planet.