1, 2 - Gray and red dacite: formed 27000 years ago when Lassen Peak first erupted...

3 - Black dacite (black to gray in coloration): formed May 14, 1915, when lava welled up into Lassen Peak's crater, sealing it off. The lava shattered during the May 19 eruption....

4- Light dacite pumice (lava filled with gas bubbles): formed May 22, 1915, when magma neared the surface and expanding gas bubbles fragmented it...

5- Banded pumice: formed May 22, 1915. by the simultaneous eruption and mixing of two magmas of different composition - light dacite and dark andesite...

(這些人太厲害了, 他們怎麼知道這些石頭是5/14還是5/22形成的呀....?!)