Sarah Allen - Postcard 1

November 19, 2007
Lake Taupo Terraces

Lake Taupo occupies a caldera, a collapsed volcanic chamber that erupted in AD 186. The caldera is much larger than the current lake level and this can be seen with the wave cut terraces (benches) that circle the lake. This photo, representing approximately 2 meters in height, shows one of these terraces. The interpretation of this site is not finite – it involves multiple working hypothesises, a common practice in geology. It could be the former edge of the lake, a fluvial or stream deposit, or a combination of both. The white pumice cobbles are well rounded and imbricated or shingled on top of each other, which is indicative of stream transport. The alternating layers of pumice and fine grained, well-sorted, sandy silt (possibly reworked volcanic ash) demonstrate a change in the energy of the system. Typically, larger particles need a higher energy environment to be moved and deposited, but it may be reversed in this case, since pumice is so porous that it floats. The fine material could also be floodplain deposits from the lake or a stream. The former shorelines/terraces can be correlated around Lake Taupo. The changes in lake level may be due to climate change, erosion, or a newly formed outlet.