Geology
The Lesser Sunda Islands consist of two geologically distinct archipelagos.
The northern archipelago, which includes Bali, Lombok, Sumbawa, Flores and Wetar, is volcanic in origin, a number of these, like Mount Rinjani on Lombok, are still active while others, such as Kelimutu on Flores with its three multi-coloured crater lakes, are extinct. It began to be formed during the Pliocene, about 15 million years ago, as a result of the collision between the Australian and the Asian plates.
The islands of the southern archipelago, including Sumba, Timor and Babar, are non-volcanic and appear to belong to the Australian plate.
The geology and ecology of the northern archipelago share a similar history, characteristics and processes with the southern Maluku Islands, which continue the same island arc to the east.
There is a long history of geological study of these regions since Indonesian colonial times;
however, the geological formation and progression is not fully
understood, and theories of the geological evolution of the islands
changed extensively during the last decades of the 20th century.
Lying at the collision of two tectonic plates, the Lesser Sunda Islands comprise some of the most geologically complex and active regions in the world.
Biodiversity and distribution is affected by various tectonic
activities. The islands of the northern archipelago are geologically
young being from 1 to 15 million years old, and have never been attached
to a larger land mass. Only Bali was part of the Ice Age continent of Sundaland, separated by the Lombok Strait from a 400-mile-long island including present-day Lombok, Sumbawa, Komodo, Flores, Solor, Adonara, and Lembata. Pantar and Alor formed a small island just to the east, while Sumba and Timor remained separate islands to the south.
Ecology
The Lesser Sunda Islands differ from the large islands of Java or Sumatra in consisting of many small islands, sometimes divided by deep oceanic trenches.
Movement of flora and fauna between islands is limited, leading to the
evolution of a high rate of localized species, most famously the Komodo dragon.
As described by Alfred Wallace in
The Malay Archipelago, the Wallace Line passes between Bali and Lombok, along the deep waters of the Lombok Strait
which formed a water barrier even when lower sea levels linked the
now-separated islands and landmasses on either side. The islands east of
the Lombok Strait are part of Wallacea, and are thus characterised by a blend of wildlife of Asian and Australasian origin in this region.
Asian species predominate in the Lesser Sundas: Weber's Line,
which marks the boundary between the parts of Wallacea with mainly
Asian and Australasian species respectively, runs to the east of the
group. These islands have the driest climate in Indonesia.
Deciduous forests
A number of the islands east of the Wallace line, from Lombok and
Sumbawa east to Flores and Alor, having original vegetation of dry
forest rather than the rain forest that covers much of the Indonesian
region, have been designated by the World Wildlife Fund as the Lesser Sundas deciduous forests ecoregion.
The higher slopes of the islands contain forests of tall Podocarpus conifers and Engelhardias with an undergrowth of lianas, epiphytes, and orchids such as Corybas, Corymborkis, and Malaxis (Adder's Mouth), while the coastal plains were originally savanna grasses such as the savanna with Borassus flabellifer
palm trees on the coasts of Komodo, Rincah and Flores. Although most of
the vegetation on these islands is dry forest there are patches of
rainforest on these islands too, especially in lowland areas and
riverbanks on Komodo, and there is a particular area of dry thorny
forest on the southeast coast of Lombok. Thorn trees used to be more
common in coastal areas of the islands but have largely been cleared.
These islands are home to unique species including seventeen endemic
birds (of the 273 birds found on the islands). The endemic mammals are
the endangered Flores Shrew
(Suncus mertensi), the vulnerable Komodo Rat
(Komodomys rintjanus), and Lombok Flying Fox
(Pteropus lombocensis), Sunda Long-eared Bat
(Nyctophilus heran)
while the carnivorous Komodo dragon, which at three metres long and
ninety kilograms in weight is the world's largest lizard, is found on
Komodo, Rincah, Gili Motang, and the coast of northwestern Flores.
Activities popular with tourists include surfing at Kuta on Lombok, hiking on Flores and Lombok, and snorkeling or diving off the Gili Islands and Labuanbajo on Flores. Urban areas in this ecoregion (which does not include Bali, Timor or Sumba) include: on Lombok the island capital Mataram and the nearby beach resort of Senggigi; on Sumbawa the port and main town of the east coast, Bima and Sumbawa Besar in the west; and the ports of Maumere (the largest town on the island), Larantuka and Ende
on Flores. Lombok and Sumbawa have surfaced roads, but the other large
island Flores is too mountainous for easy road transport. The main entry
point to the Lesser Sunda islands is Bali and there are smaller
airports at Maumere and Mataram while transport between the islands is
mainly by boat.
Threats and preservation
More than half of the original vegetation of the islands has been
cleared for planting of rice and other crops, for settlement and by
consequent forest fires. Only Sumbawa now contains a large area of
intact natural forest, while Komodo, Rincah and Padar are now protected
as Komodo National Park.
While many ecological problems affect both small islands and large
landmasses, small islands suffer their particular problems and are
highly exposed to external forces. Development pressures on small
islands are increasing, although their effects are not always
anticipated. Although Indonesia is richly endowed with natural
resources, the resources of the small islands of Nusa Tenggara are
limited and specialised; furthermore human resources in particular are
limited.
General observations
about small islands that can be applied to Nusa Tenggara include:
- a higher proportion of the landmass will be affected by volcanic activity, earthquakes, landslips, and cyclone damage;
- Climates are more likely to be maritime influenced;
- Catchment areas are smaller and degree of erosion higher;
- A higher proportion of the landmass is made up of coastal areas;
- A higher degree of environmental specialisation, including a higher proportion of endemic species in an overall depauperate community;
- Societies may retain a strong sense of culture having developed in relative isolation;
- Small island populations are more likely to be affected by economic migration.
