Abstract

Introduction

Body

Aeolian Aspect

Aeolian Studies

Coastal Aspect

Seismic Aspect

Tree-Ring Studies

Marshes

Conclusion

References

Figures

 

 

SEISMIC ASPECT

 
Currently there are studies taking place to understand the effect of earthquakes along the Alpine Fault on the coastal dunes in the Haast region.  These studies are meant to be an attempt to figure out the exact ages as well as the relative age.  Some of these studies include looking at the records of when different major earthquakes have taken place in the past 5 centuries, studying the density of the forested regions on the top of the dunes, and looking at the age of the trees in the forested region (Goff and Wells, 2006).  Then the major studies link the ages of the earthquakes with the forest ages and densities to conclude which earthquakes, in fact, caused the large periods of dune building.  The ages of the forests are measured by looking at the oldest of the trees in each forested dune and counting the tree rings. 


It is known that the majority of the sediment in the Haast region is from the alpine region to the east because of the composition of the types of schist that are present there as compared to the graywackes and other rock types in the alpine region.  The schists are shown in the Otago area as well, which is on the east side of the Southern Alps (Turnbull et al, 2001).  This tells us that the types of sediment are definitely coming from the mountainous region and spreading down both sides of the Alps.  The reason the coastal dunes only appear on the west side is because the coast is so close to the mountains that the sediment does not have a very far distance to travel before being suddenly deposited against the Tasman Sea.  On the east side of the Southern Alps the sediment must travel roughly four times as far across the plains through braided river systems, leaving much deposited in that environment much before the sediment hits the coastline.


The earthquake studies have looked at the major earthquakes that have taken place in the years 1460, 1615, 1717, and 1826, as well as some minor earthquakes that would have still been large enough to cause an influx in sediment load (Goff and Wells, 2006).  Those earthquakes are looked at the most because they were the largest, most influential on record and would therefore cause the largest change in the dune system (Goff and Wells, 2007).  The years of these four largely influential quakes are in historical geologic records and therefore the age of the dunes in relation to these four years are measureable.  With the known years on record geologists are able to know how much sediment came down in the aftermath of the earthquakes in the fault line in the Southern Alps and can link them with the corresponding quake.