Tuff Breccia

Tuff Breccia

 

a volcanogenic sedimentary rock consisting of angular or, less frequently, slightly rounded fragments of extrusive rocks that range in size from blocks of several cubic meters to particles the size of grains of sand and are cemented together by fine volcanic ash. Tuff breccia occurs in thick layers in volcanogenic formations. The origin of tuff breccia is not always clear. In many cases, tuff breccia is deposited by lahars, which are thick mudflows that accompany volcanic eruptions. (See alsoVOLCANOGENIC SEDIMENTARY ROCK.)

References in periodicals archive ?
The surrounding rocks are sandstone, sand tuff, lapilli tuff, basalt, tuff breccia, and lapilli tuff in different segments.
Span Lining Inverted Buried Surrounding number thickness arch depth rock type 1 0.70 m Yes 3m Sandstone 12 0.55 m No 25 m Sand tuff 16 0.55 m No 25 m Sand tuff 18 0.55 m No 25 m Sand tuff 20 0.55 m No 25 m Lapilli tuff 35 0.70 m No 23 m Basalt 42 0.55 m No 23 m Basalt 49 0.55 m No 23 m Tuff breccia 58 0.70 m No 23 m Lapilli tuff 65 0.70 m Yes 0m Lapilli tuff Table 2: Tunnel-lining crack index of the ten studied spans.