Waianae Range
Encyclopedia
Waianae Range is the eroded
remains of an ancient shield volcano
that comprises the western half of the Hawaiian Island
of Oahu
. Its crest, at Kaʻala, is the highest peak on Oahu at 4025 feet (1,227 m).
Like the neighboring Koolau, the Waianae Range is not a mountain range in the sense most people are familiar with, as the mountain range as a whole was created from a single volcano.
The oldest lava
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.
Interestingly, 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 odd erosion pattern is that a large landslide
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.
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
remains of an ancient shield volcano
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
that comprises the western half of the Hawaiian Island
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
of Oahu
Oahu
Oahu or Oahu , known as "The Gathering Place", is the third largest of the Hawaiian Islands and most populous of the islands in the U.S. state of Hawaii. The state capital Honolulu is located on the southeast coast...
. Its crest, at Kaʻala, is the highest peak on Oahu at 4025 feet (1,227 m).
Like the neighboring Koolau, the Waianae Range is not a mountain range in the sense most people are familiar with, as the mountain range as a whole was created from a single volcano.
The oldest lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
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
Lualualei, Hawaii
Lualualei, Hawaii is the largest coastal valley on the leeward side of Oahu in Hawaii. Inside the valley are several government communication stations including USN VLF Lualualei and the USCG Communication Station Honolulu. The closest town is Māili....
. 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.
Interestingly, 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 odd erosion pattern is that a large landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
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.