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2 February 2011
What plants really do like to live on volcanoes – and what kinds have I come across? Plant types on volcanoes could be divided into two rough categories: rock and soil dwellers. A rock dweller might thrive on a young or an old volcano, but plants that need soil are only going to do well on an older volcano (which has had time to form soil), or a tropical one (where soil formation is accelerated because of the climate). Volcanic rocks are often (but not always) full of vesicles, which makes them porous and ideal for retaining water. Volcanic soils are generally referred to as andisols, which are soils that form on volcanic ash and contain volcanic glass and compounds of elements such as Fe, Al and Si. (Ions of those elements, which are released by leaching and weathering of volcanic rock, can form complexes with organic matter; in addition to an andisol’s ability to retain water, this can make for very fertile growing conditions.) Andisols in the US are, not surprisingly, concentrated in the Cascades and northern California – where we have large stratovolcanoes and an excellent supply of volcanic ash.