Stop 1 Umatori: view of Asama

Weather permitting, we can enjoy scenic view of the whole Asama from this stop. From left to right, they are Kurofu, Maekake (Kama yama at the top), Hotoke-iwa, Ko-Asama, and Hanare-yama. A tree covered range at middle distance is made up of Neogene ignimbrites and sediments. Flat farmland at foreground represents surface of the Tsukahara debris avalanche deposit, or more likely an ancient lake dammed up by the avalanche.

Kurofu had been a symmetrical cone until 22 ka, when the eastern half collapsed to generate a large-scale debris avalanche. The avalanche, called Tsukahara, covered wide areas in the N and S lower slopes. We are standing near the edge of the deposit.

Maekake has an active crater, 400 m x 400 m, on the top, and is now growing (or ready to collapse?). Small cone surrounding the crater is called Kama-yama. The shoulders of Maekake express rims of a larger crater, 1300 m x 1000 m, which was active during the 1108 eruption.

Hotoke-iwa is not obvious because it is largely buried by younger Maekake cone. It is a flat shield of lava pile about 400 m thick built up during 20-13.6 ka.

Ko-Asama ('Ko' means small), sitting on 4 km E of the summit, is a parasitic lava dome emplaced 18 ka. The explosive eruption of the Shiraito pumice, narrowly extending to ENE, preceded the dome extrusion.

Hanare-yama (meaning isolated mountain) is another parasitic lava dome emplaced 20 ka. The eruption started with an outburst of the Kumoba pumice to S (toward us). Later a dacite lava was extruded with a tongue of a short and thick lava flow extending to SW. The net height of the lava dome is 200 m.

Stop 1 Matori: View of Asama
Stop 2 Kami Hocchi: Aira-Tanzawa ash and Asama pumices
Stop 3 Sugiuri: Tsukahara debris avalanche deposit
Stop 4 Hirahara: Hirahara ignimbrite
Stop 5 Asama Volcano Observatory: The 1783 pumice
Stop 6 Shiraito Waterfall: Shiraito pumice
Stop 7 Kuromame-gawara: Agatsuma ignimbrite of 1783
Stop 8 Oni-Oshidashi Lava Park: Oni-Oshidashi lava flow and a possible source of the Kambara event
Stop 9 Princeland: A Kambara block
Stop 10 Akagawa Quarry: Kambara debris avalanche deposit and Kusatsu pumice
Stop 11 Kambara Kan-non-do: Stone steps buried by the Kambara debris avalanche

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