Holocene coastal evolution under the influence of episodic tectonic uplift: examples from New Zealand and Japan
- Author
- Berryman, K.R; Ota, Y; Hull, A.G.
- Year
- 1992
- Journal / Source
- Quaternary International
- Volume
- 15
- Pages
- 31-45
- Summary
- Coastal geomorphology in many parts of New Zealand and Japan has been strongly influenced by tectonic uplift since the culmination of the Holocene transgression at 5.5–7 ka ago. Examples of historic coastal uplift in Japan and New Zealand, accompanied by major earthquakes provide analogues for interpreting coasts where Holocene marine terraces are arranged in staircase fashion. Despite complexities in their origin, there is commonly only one shore platform for each relative stillstand of sea level. Shore platforms are subhorizontal, and are usually graded to low tide level. The width of platforms depends primarily on the erodibility of bedrock and the length of time available for formation. The simplest setting for assessing the influence of uplift on coastal evolution requires readily erodible, homogeneous bedrock, and a microtidal environment so that wide shore platforms of limited surface relief can be cut within ± 1.0 m of mean sea level. Earthquake-related uplift (where uplift is greater than the tidal range) is an instantaneous and catastrophic event that overwhelms on-going processes of shore platform formation. Determining the degree of tectonic control on coastal evolution is more difficult where hard or layered, dipping, bedrock exists or where the coast is subject to spatial variation in wave energy. Temporal and spatial variation in wave energy and variation in sediment supply make beach ridges more difficult to relate to former sea-level positions than either hard or soft bedrock platforms. More precise measurement of past uplift events are possible in coral reef environments than at higher latitude sites because coral reef colonies grow within ± 0.10 m of the mean low water spring tide and are sensitive to sea-level changes.