square kilometres around the islands. Lipman et al.
(1988) and Moore et al. (1989) were amongst the first
authors contributing indisputable evidence of the
existence of many giant landslides in the Hawaiian
archipelago. Later, such giant landslides have been
identified in several volcanic islands around the
world (Table 2.6). Extensive deposits in the sea
around oceanic islands can also be produced by
pyroclastic flows (Hart et al. 2004), or indeed by a
combination of landslips and volcanic ejecta.
Major volcanic slope failures are fairly common
globally, occurring at least four times a century and
they are a particular feature of volcanic islands in
excess of 1000 or 1500 m height (Hürlimannet al.
2004). As many as 20 mega-landslides, with volumes
varying between 30 and 5000 km^3 , have been recog-
nized both for the Canaries (Canals et al. 2000) and for
Hawaii (Fig. 2.22; Moore et al. 1994). These events are
reiterative in actively forming islands. For example,
El Hierro, the youngest of the Canaries, with an age
slightly greater than 1 million years, has already suf-
fered four such catastrophic events, the last of them
(El Golfo landslide c.15 000BP), carried more than
half the island into the sea (Carracedo et al. 1999).
Similarly, the La Orotava valley slide on Tenerife is
estimated to have been up to 1000 m in thickness,
and created an amphitheatre up to 10 km wide and
14 km long and an offshore prolongation several kilo-
metres in length (Hürlimannet al. 2004). The fre-
quency of recurrence of large landslides on the
Canaries has been about one per 100 000 years across
the whole archipelago, or once every 300 000 years
for each single island (Masson et al. 2002).
Hürlimannet al. (2004) suggest that there are four
key factors controlling where mega-landslides
occur on volcanic islands:
●the development of deep erosive canyons on the
flanks of the volcano
●the presence of high coastal cliffs eroded at the
base by wave action
●the presence of widespread residual buried soils
from an earlier phase of the development of the vol-
cano, providing a line of weakness
●the orientation of structural axes.
Such landslides can modify the subsidence regime
of the affected islands, as well as promoting new
volcanic activity, mainly centred in the summit scars
(Ancocheaet al. 1994). When not eroded or buried
by the emission of new volcanic material, the scarsNATURAL DISTURBANCE ON ISLANDS 43Table 2.6Examples of large debris-avalanche landslides occurring around young volcanic islands (slightly modified from Canals et al. 2000 and
Whelan and Kelletat 2003)
Island Landslide Vertical distance Sea floor Volume Event age
name moved (m) area covered (km^2 ) (km^3 ) (ky)
Réunion Ralé-Poussée 1700 200 30 4.2
Réunion Eastern Plateau 3000 – 500 15–60
100–130
Fogo (C. Verde) 1200 – 100 10
El Hierro El Golfo 5000 1500 400 15–20
and 100–130
El Hierro El Julan 4600 1800 130 160
El Hierro Las Playas II 4500 950 50 145–176
La Palma Cumbre Nueva 6000 780 200 125–536
Tenerife Güímar 4000 1600 120 780–840
Tenerife La Orotava (Icod) 2100 500 540–690
Tenerife Las Cañadas 4000 1700 150 150–170
Kauai South Kauai 4000 6800 – 13
Kauai North Kauai 4000 14000 – –
Oahu Nuuanu 5000 23000 5000 –
Hawaii Pololu 4000 3500 – 370
Hawaii Alika 1–3 4800 4000 2000 247