(A satellite view of  Kauai)

The island of Kauai today is the result of many natural processes, which resulted in the creation of the beautiful landform that both natives and tourists admire. 

We can attribute Kauai’s unique and diverse land formations to its volcanic origin.  Kauai was formed around 6 million years ago by tectonic plates moving over a stationary hotspot in the Earth’s mantle.  A hotspot is an area of hot magma located under the Earth's surface.  It creates stationary heat and energy, known as mantle plumes.  This causes seamounts, which over millions of years rise above the surface and form an island.

(Depicting the hot spot theory)

One characteristic of hotspots is that they produce fluid basaltic lava flows, which are extrusive, meaning the lava is thin and runs away from the vent forming a large land mass with gently sloping sides. This process created the shield volcano, which is Kauai. 

The crystallization and cooling of basaltic lava around the  lava channels can be referred to as pāhoehoe flows.  Active low-viscosity lava flow forms a roof  above the still moving stream of lava.  Some lava tubes, like Kauai’s Spouting Horn, form blow holes.  As depicted below, the pressure from the waves in combination with an influx of air creates an eruption of water through the tube and out a hole.  

Rainbows often form in the incandescent spray of the lava tube at sunset.  This is a magnificent sight!  It is easy to understand why early Hawaiians created meaningful legends about this marvelous natural wonder.

                                              

When water is forced into the lava tube by the surf, it erupts into the air creating the hissing noise you hear.  People think Spouting Horn sounds and looks similar to a whale’s spout, hence its name.  When the tide is high, these erruptions can shoot as high as 50 feet. 

(Waimea Canyon)

Waimea Canyon, another renowned geologic formation in Kauai is known as the Grand Canyon of the Pacific.  This canyon is 1 mile wide, 10 miles long and an estimated 3,500-feet deep.  The translation of Waimea means “reddish in color.”  This name is very appropriate because the first thing one notices about the canyon is the rich red erosions covering the canyon’s walls.  The erosions which are exposed basalt have been weathered from their original black color to the red we see today.  The history Waimea’s formation is unique because it was created both by the steady process of rainwater flowing down from Mt. Wai’ale’ale, as well as by the catastrophic collapse of the volcano, Olokele, which created Kauai.

While Olokele, was still erupting, a portion of the island collapsed.  This collapse formed deep indentations in the land, which then filled with lava flows and became Waimea Canyon.  

The canyon is divided by a fault.  As a result, one side of the canyon is actually lower than the other.  The differences in the altitude of the fault line’s division have resulted in unique and different forms on both sides. The cliffs on the west side of the canyon are made up of remnants from thin lava flows. The oposite side of the canyon has walls, which are built from thick lava flows that formed pools in the depression.  

(Notice the stratigraphy and erosion along the canyon's walls)

               

Sources 

Earth Observatory.nasa.gov

Volcanoes.pdf

Lava Tubes

Geology of Hawaii