Penitentes

Tall, thin spikes of hardened snow or ice, packed closely together in fields and often reaching several feet or more in height, formed in high-altitude, cold, dry environments where intense sunlight causes snow to sublimate directly into water vapor rather than melt. Uneven sublimation, amplified as sunlight reflects between adjacent forming spikes, gradually sharpens the field into its distinctive blade-like shapes, most famously across parts of the high Andes.