Andosols occur throughout the world where volcanic activity is common, especially in the circum-Pacific region and along the mid-Atlantic Ridge.
Soils with a vitric or andic horizon (slightly to moderately weathered horizons in pyroclastic deposits dominated by short-range-order minerals, notably allophane and imogolite) starting within 25 cm from the soil surface. In addition, they may have a histic, fulvic, melanic, mollic, umbric, ochric, duric, or cambic horizon. Other diagnostic horizons (unless buried deeper than 50 cm by volcanic deposits) are absent.
Yellow tuff deposits (“tufo giallo”), about 12 000 years old and of Vesuvian origin, overlying Cretaceous limestone near Lago del Matese, Italy