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.
A slightly weathered Andosol with an acid, humus-rich surface layer near Lago del Matese, Italy (Umbri-Vitric Andosol; ISRIC reference soil IT 016)
Yellow tuff deposits (“tufo giallo”), about 12 000 years old and of Vesuvian origin, overlying Cretaceous limestone near Lago del Matese, Italy