A landscape carved by ice
In the Hengduan Mountains of Sichuan, the Yading Nature Reserve contains a dramatic landscape shaped by repeated glaciations. The reserve is defined by three sacred peaks considered emanations of bodhisattvas in Tibetan Buddhism. These are Chenrezig (Avalokiteśvara), the highest at 6,032 meters (19,790 feet), Jambeyang (Manjushri) at 5,958 meters, and Chanadorje (Vajrapani), also at 5,958 meters (19,547 feet). These granite peaks, examples of glacial horns, anchor a region filled with U-shaped valleys, arêtes, and cirques—all evidence of extensive ice cover during past ice ages.
This landscape records of the Quaternary glaciation, an ongoing period of alternating glacial and interglacial phases that began 2.58 million years ago. During colder periods, glaciers advanced down these valleys, scouring the bedrock and pushing debris into large ridges. When the climate warmed, the glaciers retreated, leaving behind these ridges as moraines. The park preserves a rare and extensive sequence of these moraines, which records the timeline of regional climate change.
Reading the boulders
The ages of these moraines are determined using a technique called cosmogenic nuclide surface exposure dating. As cosmic rays—high-energy particles from space—bombard the Earth's surface, they trigger nuclear reactions in the quartz crystals of granite boulders left behind by glaciers. These reactions produce rare isotopes, particularly Beryllium-10 (¹⁰Be). The concentration of ¹⁰Be in a boulder's surface shows how long the rock has been exposed since the ice that carried it melted away.
By sampling boulders from different moraines, geologists can reconstruct the timing of multiple glacial advances. Studies across the Tibetan Plateau have used this method to establish chronologies for major glacial periods. Evidence points to significant glacial advances during several Marine Isotope Stages (MIS), which are global climate periods identified from deep-sea sediment cores. The moraines in this region correspond to the Last Glacial Maximum (MIS 2, around 20,000 years ago), the Penultimate Glaciation (MIS 6, around 130,000–190,000 years ago), and even older events, with some glacial stages on the plateau dating back to MIS 12 (around 480,000 years ago). The successive, nested moraines at Yading provide a nearly continuous record of these climate oscillations, showing how glaciers in this sensitive high-altitude environment responded to global temperature swings over the last half-million years.