A layer of ice crystals, usually cup-shaped and facetted, formed by vapour transfer (sublimation followed by deposition) within dry snow beneath the snow surface. Depth hoar is associated with very fast crystal growth under large temperature gradients. Sometimes a layer of depth hoar forms just above, and may assist in identifying, the summer surface. The low density and low strength of depth hoar can make it difficult to retrieve unbroken core sections during coring, and can complicate estimates of accumulation by microwave remote sensing. Layers of depth hoar also increase the likelihood of avalanching.