12.10 Erosion Triggered by Earthquake and Tsunami
211
Ice Age, would already have been endemic. Direct destruction of crops by tsunamis
may have occurred in some areas in addition to a nationwide destruction of biota
consequent on erosion, salt water inundations and landslides from multiple fault
ruptures.
James Goff and Bruce McFadgen [27] suggest that we need to add insights from
recent studies of the tectonic history of New Zealand and a history of significant
tsunami inundation to our understanding of the erosion history of New Zealand.
Where Grant assigns major periods of river aggradation and coastal dune building
to “changes in river systems caused by increased rainfall induced by changes in
airflow and atmospheric warming over New Zealand” they argue that
Recent palaeoseismic research, however, leads us to suggest that there may be a tectonic
link. We propose that the Matawhero river aggradation event (Grant, 1985), the Ohuan
Chronozone of coastal dune building (McFadgen, 1985) and the Kekerionean (coastal
dune) Depositional Episode (McFadgen, 1994) form part of a sequence of environmental
outcomes that were generated by a cluster of large earthquakes (pp. 2230–2231).
They identify a specific earthquake cluster: “At least five, probably large, earthquakes have been identified (there might be more) that relate to fault rupture around
the 15th Century AD.” And they conclude, after considering evidence relating to
these earthquakes:
If our model is correct, then the cluster of 15th Century AD earthquakes stands out as a
New Zealand-wide catastrophe, causing tsunami, catastrophic erosion of hill slopes, river
aggradation, rapid coastal dune building, and abandonment of coastal settlements. When
viewed in the light of Holocene landscape change in New Zealand we consider that this,
and possibly earlier and later clusters of seismic activity, should be recognized as a major
driver of change in geomorphology, vegetation and human settlement (p. 2234).
Goff and McFadgen, further, link the 15th century event with a major El Niño
in AD 1450, suggesting earthquake, tsunami and climate as concomitant factors
triggering massive erosion in the mid-15th century.
A geo-environmental report prepared for the Wellington Regional Council [28]
suggests how the environmental destruction caused through the warm-wet periods
that Grant charts has been drastically reinforced by erosion caused by earthquakes
and tsunami:
In brief, seismic activity immediately generates tsunami and landslides. Sediment flow
down rivers causes an increase in fine material reaching the nearshore zone and a period
of rapid coastal dune building takes place, while coarser material forms river aggradation
surfaces. Prehistoric coastal Maori settlements suffer from tsunami inundation, sediment
smothering of shellfish beds, and loss of land due to landsliding and aggradation (Goff and
McFadgen, 2001).
In AD 1450 the environmental destruction caused by an earthquake cluster and
nationwide tsunami can only have intensified erosion and the loss of biota, aggravating climate-driven starvation and conflict over land and resources. Also inevitably
it would have led to a nationwide destruction of archaeological evidence. Earlier
earthquakes and local and nationwide tsunamis must also have destroyed archaeological evidence. Though smaller earlier populations, with much higher ceilings
211
Ice Age, would already have been endemic. Direct destruction of crops by tsunamis
may have occurred in some areas in addition to a nationwide destruction of biota
consequent on erosion, salt water inundations and landslides from multiple fault
ruptures.
James Goff and Bruce McFadgen [27] suggest that we need to add insights from
recent studies of the tectonic history of New Zealand and a history of significant
tsunami inundation to our understanding of the erosion history of New Zealand.
Where Grant assigns major periods of river aggradation and coastal dune building
to “changes in river systems caused by increased rainfall induced by changes in
airflow and atmospheric warming over New Zealand” they argue that
Recent palaeoseismic research, however, leads us to suggest that there may be a tectonic
link. We propose that the Matawhero river aggradation event (Grant, 1985), the Ohuan
Chronozone of coastal dune building (McFadgen, 1985) and the Kekerionean (coastal
dune) Depositional Episode (McFadgen, 1994) form part of a sequence of environmental
outcomes that were generated by a cluster of large earthquakes (pp. 2230–2231).
They identify a specific earthquake cluster: “At least five, probably large, earthquakes have been identified (there might be more) that relate to fault rupture around
the 15th Century AD.” And they conclude, after considering evidence relating to
these earthquakes:
If our model is correct, then the cluster of 15th Century AD earthquakes stands out as a
New Zealand-wide catastrophe, causing tsunami, catastrophic erosion of hill slopes, river
aggradation, rapid coastal dune building, and abandonment of coastal settlements. When
viewed in the light of Holocene landscape change in New Zealand we consider that this,
and possibly earlier and later clusters of seismic activity, should be recognized as a major
driver of change in geomorphology, vegetation and human settlement (p. 2234).
Goff and McFadgen, further, link the 15th century event with a major El Niño
in AD 1450, suggesting earthquake, tsunami and climate as concomitant factors
triggering massive erosion in the mid-15th century.
A geo-environmental report prepared for the Wellington Regional Council [28]
suggests how the environmental destruction caused through the warm-wet periods
that Grant charts has been drastically reinforced by erosion caused by earthquakes
and tsunami:
In brief, seismic activity immediately generates tsunami and landslides. Sediment flow
down rivers causes an increase in fine material reaching the nearshore zone and a period
of rapid coastal dune building takes place, while coarser material forms river aggradation
surfaces. Prehistoric coastal Maori settlements suffer from tsunami inundation, sediment
smothering of shellfish beds, and loss of land due to landsliding and aggradation (Goff and
McFadgen, 2001).
In AD 1450 the environmental destruction caused by an earthquake cluster and
nationwide tsunami can only have intensified erosion and the loss of biota, aggravating climate-driven starvation and conflict over land and resources. Also inevitably
it would have led to a nationwide destruction of archaeological evidence. Earlier
earthquakes and local and nationwide tsunamis must also have destroyed archaeological evidence. Though smaller earlier populations, with much higher ceilings