A relic of the ice age
In the high peaks of the Tateyama Mountains, what appears to be simple fields of rock and debris are "rock glaciers"—a mix of rock, soil, and interstitial ice behaving like a very slow-moving river. This is relict permafrost, a frozen legacy from the colder climates of the Pleistocene epoch. Permafrost is ground that remains at or below 0°C for at least two consecutive years. The features in Tateyama exist at the southernmost limit for permafrost in Japan, making them an indicator of climate change.
These formations are not glaciers, which are masses of flowing ice. Instead, the ice acts as a cement between boulders and soil, allowing the entire landform to deform and creep downslope under its own weight. Scientific monitoring has confirmed their movement. GPS measurements of similar ice masses in the Tateyama range, such as in the Gozenzawa ravine, have recorded movement of 6 to 30 centimeters per month. The ice thickness within these features can exceed 30 meters. This permafrost is found at elevations above 2,600 meters, often on shaded, north-facing slopes where it is insulated from summer heat.
Monitoring a changing climate
The Tateyama permafrost is important for scientific study. Its existence depends on a delicate balance of cold winter temperatures and sufficient snow cover to insulate the ground from warmer summer air. As global temperatures rise, this balance is threatened. Projections indicate that the environmental conditions needed to sustain permafrost in the Northern Japan Alps could disappear within the next two to three decades.
The thawing of this ancient ice has several consequences. It can affect the stability of mountain slopes, potentially altering the landscape. It also impacts the unique alpine ecosystems that depend on the cold ground conditions. The rock ptarmigan (Lagopus muta), a bird remnant of the last ice age, lives in this environment. Studying the rate of thaw and movement provides scientists with data on the regional effects of climate change. The permafrost here is from a past world, one that is vanishing.