THE ANTHROPOCENE: OBSERVATIONS AND EXPECTATIONS FOR COASTAL EVOLUTION AND SEDIMENTARY RECORDS

Both the 2011 tsunami in the Tohoku area and the February 2011 Earthquake in Christchurch have brought a wealth of information on the Anthropocene direct and indirect impacts on sedimentary records, and also on how the sediment dynamics may change during the Anthropocene.

The first concept addressed in this presentation concerns the modification of the sedimentary records of events by coastal human activity. As the 2011 tsunami struck the coast of Japan, I have investigated the sediment deposits of the tsunami from both primary and secondary data, in order to characterize the type and the thickness of deposits of the present previous tsunami. The research has shown that the tsunami deposits have been thinning during the historical period, even for tsunamis of similar orientation and from similar sedimentary stocks. This phenomenon is to be linked with the development of coastal structures and human settlements. Human beings, therefore, by their activities have modified the sedimentary signature of tsunami events.

The second concept works the other way around with the change in sedimentary dynamics impacting human activities. The earthquake of 2011 in Christchurch, New Zealand has experienced up to a meter of subsidence in the coastal area, resulting in the equivalent of 100 years of relative sea-level rise. This has provided an excellent laboratory to test the impacts of sea level rise on sediment dynamics in the river systems and on land. Although the observations only span for the last 4 years, we have seen the extension of the tidal influence in the coastal streams and the decrease of energy available to transport sediments. At the same time, the higher base-level has modified the water pathways on land and its ability to conduct water away from land, generating new flood patterns. As there is an increased stock of sediments in the coastal waterways, the dynamic of the Estuary is bound to be modified as well, generating chain-effects that aren't fully predictable yet.