How did the Hawaiian islands form?

A key reference is Professor Michael E. Wysession of Washington University in St Louis.

The Hawaiian Islands are far away from any continental land mass. The furthest such island though is Pitcairn Island. Hawaii took an exceedingly long time to be discovered. It was first visited by Polynesians around 300 CE. Polynesians’ origin is southeast China in the Fuzhou basin. Starting around 5500 years ago, they travelled progressively east to Taiwan, Philippines, Indonesia, Solomon Islands, Vanuatu, Samoa, Tonga, French Polynesia and eventually north to Hawaii.

Hawaii is at one end of the Hawaiian-Emperor Seamount Chain, which is a mostly submerged mountain range in the Pacific Ocean. A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level). The chain stretches 3,600 miles across the western Pacific Ocean. This chain has two parts. Starting from the Big Island of Hawaii, it mostly goes west-northwest in a straight line for 1500 miles. This section is called the Hawaiian Seamount Chain. After that there is a curious sharp bend. It then goes mostly north northwest in a straight line. This part is called the Emperor Seamount Chain.

Let us trace the chain heading west. The chain ends at the Kama’ehuakanaloa seamount (formerly Lōʻihi), the youngest volcano in the chain, which lies about 22 miles southeast of the Big Island of Hawaii. The Big Island is less than a million years old and still incredibly young. The next cluster of Hawaiian Islands are Maui, Lanai, and Kahoolawe (a bit over a million years old). Next is Molokai (about 2 million years old). Next in the chain is Oahu (about 3 million years old). Next in the chain is Kauai (about 5 million years old). Next in the chain is Niihau (about 6 million years old). This is the last major island of the state of Hawaii. The chain continues to encompass at least 130 odd islands/islets/rocks/atolls/shoals/reefs, which are progressively 12 million years, 28 million, all the way to the bend where they are 43 million years old. The Midway atoll is on this chain. Then in the Emperor seamount after the bend, they are progressively 47 million, 55 million, 65 million all the way to 85 million years old at the other end, at the Aleutian Trench off the coast of the Kamchatka peninsula where subduction is occurring (more on subduction later). Older seamounts than that have already been subducted. Subduction is where one tectonic plate converges with a second plate, and the heavier plate dives beneath the other and sinks into the mantle.

Before this seamount chain started forming how did the continents themselves form through tectonic plate movements? We have to go much further back in time to a supercontinent called Pangea that existed that incorporated almost all the landmass on earth. Pangea was surrounded by a global ocean called Panthalassa, and it was fully assembled by the Early Permian epoch (some 299 million to about 273 million years ago). The supercontinent began to break apart about 200 million years ago, during the Early Jurassic Epoch (201 million to 174 million years ago), eventually forming the modern continents and the Atlantic and Indian oceans. 

The continents rest on plates made of a layer of the Earth's crust and its mantle, known collectively as the lithosphere. Plates are different sizes, with some plates more than 124 miles (200 km) thick. Below the lithosphere is a ductile layer of rock called the asthenosphere. The plates are rigid slabs almost floating along in the asthenosphere. Scientists do know four different ways the plates move.

• Two plates can move away from each other.
• Two plates can collide.
• One plate can be pushed under another plate. (subduction)
• Plates can slide past each other sideways.

The Earth’s tectonic plates are constantly moving. However, this movement is slow, and rates vary from less than 2.5cm /yr to over 15cm/yr. Tectonic plates move as the asthenosphere, which is ductile, is weak enough to accommodate the movement of the solid and brittle plates above it. Three theories have been put forward for the movement of tectonic plates on top of the asthenosphere. None have been completely proven. I will note them but not elaborate. The theories are:

• convection currents
• ridge push
• slab pull

Hotspots are volcanic locales thought to be fed by underlying mantle that is unusually hot compared with the surrounding mantle. Examples include the Hawaii, Iceland, and Yellowstone hotspots. A hotspot's position on the Earth's surface is independent of tectonic plate boundaries, and so hotspots may create a chain of volcanoes as the plates move above them. Hotspots tend to move very slowly and can be considered somewhat fixed with respect to the earth’s deep mantle. Tectonic plates on the other hand move over an order of magnitude faster relative to the deep mantle. Hotspots move so slowly that they can serve well as a global reference plane to study how plates move relative to the deep mantle over huge time scales.

There are two hypotheses that try to explain hotspot origins. This gets technical!! The more common one suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary (A diapir is a type of intrusion in which a more mobile and ductile material is forced into brittle overlying rocks). The alternative plate theory is that the mantle area beneath a hotspot is not unusually hot, rather the crust above is unusually weak or thin, so that lithospheric extension allows the passive rising of molten rocks from shallow depths (Lithospheric extension is a fundamental plate tectonic process controlling the collapse of mountain belts, the break-up of continents and the formation of new oceanic basins). Seismic images consistent with the evolving mantle plume theory now exists using a new global tomography approach.

Tomography uses seismic waves travelling through rocks to sense the parts of the mantle that are hot. This is a powerful innovative technology!! The waves travel slower through hot areas. There is a huge hot area beneath Africa in the mantle. There is also one in the pacific under Hawaii. The core is molten and does not move past the core/lower mantle boundary. It is heat that is transmitted from the core. The relationship between these Tomography heat map images and mantle plumes is still being studied. 

To understand how the Hawaiian-Emperor Seamount chain formed, you need to understand both tectonic plates and earth hotspots. Before 43 million years ago the pacific plate was moving north-northwest – the same direction as the Emperor Seamount chain. After that the movement changed to a more west-northwest direction – the same direction as the Hawaiian Seamount chain. A volcano forms on a tectonic plate above a hotspot. The Hawaiian hotspot threw up seamounts and volcanic islands in a straight-line chain as the pacific plate moved. The hotspot is now under the big island and Kama’ehuakanaloa. This is the story concisely.

Where is the moving Pacific plate going? It is subducting under the American plate up near the arctic. The Aleutian Trench is an oceanic trench along a plate boundary which runs along the southern coastline of Alaska and the Aleutian Islands. The trench extends 2,100 miles. The subduction along the trench gives rise to the Aleutian Arc, a volcanic island arc, where it runs through the open sea west of the Alaska Peninsula. The trench forms part of the boundary between the Pacific plate and the North American plate. Here, the Pacific plate is being subducted under the North American plate at a dip angle of nearly 45°. The rate of closure is 3 inches per year. 

Why did the pacific plate change direction 43 million years ago? The explanation by geologists may be that another plate called the Kula plate finished completely subducting under the American plate at that time. This rearranged the inter-plate relationships in the Pacific. But more study is needed. 

The Hawaiian hotspot is the hotspot on earth that has emitted the most material for the longest time from a single spot. In the last 80,000 years it has emitted at least 1 million cubic kilometers of material. The estimated volume of lava produced on the Big Island alone is in the range of 50,000 to 70,000 cubic kilometers. The long-term rate of volcanic activity is around 0.1 to 0.3 cubic kilometers of lava per year for the Big Island of Hawaii. 

Some other notable examples where a similar hotspot triggered chain formation process has been in operation are:

1.   Louisville Ridge, which stretches over 2500 miles and has over 70 seamounts. This is found off New Zealand/Tonga and caused by a hotspot as the pacific plate subducts under the Australian plate. The Louisville hotspot is believed to lie close to the Pacific-Antarctic Ridge although its exact present location is uncertain.

2.   The New England hotspot track in North America (also referred to as the Great Meteor hotspot) that stretches beyond Hudson Bay in Canada, through New England, to beyond the Mid Atlantic Ridge on the African plate. It is over 3700 miles. The New England Seamount chain that is part of it is the longest chain in the North Atlantic. The northwestern end in Canada is over 200 million years old. The Mid-Atlantic Ridge passed over the hotspot around 76 million years ago and renewed volcanic activity produced the Seewarte Seamounts on the African Plate between 26 and 10 million years ago. It ends at the Great Meteor Seamount south of the Azores, where it is found today. It is the longest continuously running hotspot. 

3.   Ninety East Ridge originates west of the Andaman and Nicobar Islands and extends 3100 miles in the Indian Ocean and goes roughly north to south along the 90^th median from the Bay of Bengal all the way down to the southern hemisphere not far from Antarctica around 31 degrees south latitude. The age progression is from 82 million years in the north to 37 million years to the south. It has an average width of 120 miles. There are however some inconsistencies with the hypothesis of an ageing mantle plume origin for all of the ridge.

4.   Chagos-Laccadive Ridge is also in the Indian Ocean and also goes roughly north to south and tilts west lower down. The Maldive archipelago is found on this chain. The age progression is down from 65 million years in the north, jump over the mid ocean ridge, and the hotspot is currently located off the coast of Madagascar in Reunion Island. The CLR is asymmetrical with a steeper eastern slope and has an average depth of less than 3,300 ft. It formed south of or near the Equator together with the remaining western continental margin of India when India separated first from Madagascar in the Mid-Cretaceous and then from the Seychelles Islands in the Late Cretaceous.

It is interesting and educational to look at the youngest Hawaiian island which is the big island which is still geothermally active and still being shaped. It also has a number of unique features. Older islands further along the chain have experienced more weathering and ageing with time and have things like rich vegetation due to fertile soil, more lifeform diversity, extinct volcano craters, and beautiful beaches filled with sand. Kauai is called the garden island and has a fertile soil and has the wettest spot on earth. Oahu is full of these beautiful sandy beaches. Punchbowl (last erupted 75,000 years ago) and Diamond Head (last erupted 300,000 years ago) are extinct volcano craters on Oahu. Such things are less common on the big island and contrasts between different areas in the island can be quite stark.

The big island is the largest of the Hawaiian Islands. It is about 4028 sq miles. It is the world’s second highest island (New Guinea is the highest). It looks like a shield laid flat. There are 5 volcanoes that make up the island. Mauna Kea towards the north is about 13,796 feet from sea level but also about 33,500 feet tall from the base in the ocean floor. It is the tallest of any type of mountain. It is a dormant volcano with the last eruption 4500 years ago. Its summit has truly clear skies and is ideal for astronomy. Moana Loa is to the south and about 13,680 feet from sea level and 30,085 feet tall from the base. It is the largest active volcano on Earth and the planet's third largest volcano behind Puhahonu which is also in the Hawaiian chain, and the Tamu Mastif (990 miles east of Japan). The last eruption lasted for 12 days in 2022. This was the first eruption since 1984. Kilauea in the southeast is an active volcano. It last erupted in December 2024, and it is continuing into 2025. The lava here tends to be very fluid. Sometimes a lava lake forms in the Halemaumau crater of Kilauea which is quite impressive to see. A great experience is to drive around the crater rim in Kilauea. The island added 875 acres in the southeast last year due to volcanic activity. It destroyed over 700 homes, including the home belonging to the mayor of Big Island, and millions of dollars of damage. After Mauna Loa and Kilauea, Hualalai is the third most active volcano situated in the northwestern part of the Big Island of Hawai’i. In the last 1,000 years, the Hualalai volcano has erupted at least three times. Its peak stands 8,271 feet above sea level. The Kohala volcano is to the north and last erupted about 120,000 years ago. It is considered to be extinct. 

There are many varied ecosystems on the big island, and they offer great contrasts. 

1. The Big Island’s rainforests are truly magical realms teeming with life. This is mostly in the northeast around Hilo. There are a number of waterfalls and Akaka Falls are magnificent. 
2. There are underwater ecosystems too. It’s warm, crystal-clear waters harbor exquisite coral reefs and an array of marine life that beckons to be explored. Kealakekua Bay and Honaunau Bay are renowned snorkeling and diving spots. 
3. Hawaii Volcanoes National Park is the ultimate destination to see the raw power of active volcanoes. Here, life has adapted to thrive in the face of constant volcanic activity, creating a unique and resilient ecosystem. 
4. As you ascend to higher elevations, you’ll encounter montane forests, with cooler temperatures and an exclusive set of plant species, including the iconic Silver Sword. The top of Moan Kea also often has snow. 
5. On the island’s leeward side, you’ll find subtropical dry forests, where flora and fauna have adapted to arid conditions. These areas are home to unique species that have learned to flourish despite challenging circumstances. 
6. The Kohala Coast is known for its open grasslands and dry shrublands. There is actually cattle ranching in these parts with Parker Ranch and Kahua Ranch among the bigger ranches. 
7. The Kona side includes various agricultural ecosystems. From coffee plantations to macadamia nut farms. 

There are few beaches, but there are at least two very contrasting beaches that people can enjoy. Hapuna on the northwest is a beautiful white sands beach. Kalapana on the southeast is a black sands beach crafted by the volcano. 

To give future Moon-walking astronauts more familiarity with the subject, several locations were found by NASA for geology training. The volcanic terrain at several sites on the Big Island was ideal for training Apollo astronauts. 

When you think of cowboys you might think of the Wild West or movie-style shootouts, but not many people would think of Hawaii. And yet, Hawaiians have a long, proud history of cattle ranching and cowboys, known on the islands as paniolos. Parker Ranch in the Kohala region was founded in 1847 and is one of the oldest ranches in the United States, pre-dating many mainland ranches in Texas and other southwestern states by more than 30 years. Kahua Ranch on Kohala Mountain is one of the most beautiful ranches on the Big Island with 2,100 acres covering 6 precipitation zones stretching from the rain forest at 3,500 feet to the ocean. Kahua Ranch Ltd. is home to one of the largest herd of cattle on the island with over 1000 mother cows at any given time. 

Big Island boasts several renowned macadamia nut farms that produce some of the finest nuts and welcome visitors for a unique farm-to-table experience. Each farm has its specialties and attractions, adding to the diversity of the island’s macadamia nut farm touring experience. One of the most prominent names is the Mauna Loa Macademia Nut Corporation, with a history dating back to 1949 and an expansive orchard that impresses every visitor. On the other hand, the Hamakua Macadamia Nut Company, known for its commitment to sustainability and quality, offers a delightful range of flavored macadamia nuts. Ahualoa Farms presents a smaller-scale, intimate farm experience for those interested in organic farming. These, along with other farms, offer a variety of touring experiences to cater to the different interests of visitors.

Kailua Kona lies smack in the middle of coffee country on the Big Island. This is the home of Kona coffee: a scenic, tropical and narrow region on the slopes of the Hualalai and Mauna Loa volcanoes in the north and south Kona district.

The Big Island of Hawaii is a treasure trove of diverse ecosystems, each with its own unique beauty and natural wonders. From verdant rainforests, dry forests, high elevation ecosystems, vibrant coral reefs, dry shrublands, agricultural systems, and dynamic volcanic landscapes, this island offers an astonishing array of experiences.

In retirement, most of our vacations are somewhere on the islands. We do visit the big island at least once a year.