T E P H R A
June 1998  -  Volume 17
TEPHRA n. fragmented rock, ash etc. ejected by a volcanic eruption, [from the Greek word for ash]
Concise Oxford Dictionary
The Falling Mountain landslide involved 72 million cubic metres of rock.  It is 10 km from Arthur's Pass, and was triggered by the 1929 Arthur's Pass earthquake (magnitude 7.1).  The rock fell about 1200m, and flowed 4.5 km rapidly down the valley, trimming off the bush as it went.

Why does New Zealand have lots of earthquakes?
by Martin Reyners   Institute of Geological and Nuclear Sciences

The how, what and where of an earthquake
by Warwick Smith   Institute of Geological and Nuclear Sciences

The where and when of New Zealand earthquakes
by Lee Aitken, Terry Webb   Institute of Geological and Nuclear Sciences

How much will it shake where you live?
by Mike Kozuch, Graeme McVerry  Institute of Geological and Nuclear Sciences
     John Taber  Victoria University of Wellington