Waianae Range (sometimes referred to as the ''Waianae Mountains'') is the

eroded Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust, and then sediment transport, tra ...

remains of an ancient

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...

that comprises the western half of the

Hawaiian Island The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost Ku ...

Oahu Oahu () (Hawaiian language, Hawaiian: ''Oʻahu'' ()), also known as "The Gathering place#Island of Oʻahu as The Gathering Place, Gathering Place", is the third-largest of the Hawaiian Islands. It is home to roughly one million people—over t ...

. Its crest, at

Kaʻala Kaala or Mount Kaala (pronounced in Hawaiian) is the highest mountain on the island of Oahu, at . It is a part of the Waianae Range, an eroded shield volcano on the west side of the island. The FAA maintains an active tracking station at the s ...

, is the highest peak on Oahu at . Like the neighboring Koolau, the Waianae Range is not a

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arise ...

in the sense most people are familiar with, as the mountain range as a whole was created from a single volcano rather than plate tectonics. The oldest

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

dated from the volcano are about 3.9 million years old. About 3.2 million years ago, the volcano's activity changed, the rate of eruption started to decrease and the composition of the lava erupted from the volcano changed. The volcano is thought to have last erupted about 2.5 million years ago. When active, the Waianae volcano's center of activity was at present-day Lualualei Valley. Intense erosion on the western flank of the mountain has destroyed much of those flanks. Thus, the mountain today is much smaller than it was when the volcano was active. While the western part of the mountain has been destroyed by erosion, the eastern part is still in a youthful stage of erosion. This is considered somewhat strange by some geologists since the western part of the volcano is on the leeward side of the island; thus, most rain falls on the eastern side of the volcano. Given this information, more erosion would be expected on the eastern portion of the mountain. One theory to explain this erosion pattern is that a large

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

cut away the western portion of the volcano. The faults from this huge landslide weakened the rock, making the western part of the mountain much more susceptible to erosion than the eastern side.

References

External links

* {{Hawaiian volcanism Volcanoes of Oahu Extinct volcanoes Mountains of Hawaii Landforms of Oahu Polygenetic shield volcanoes Hawaiian–Emperor seamount chain Pliocene shield volcanoes Pleistocene shield volcanoes Neogene Oceania Cenozoic Hawaii