Stepping off a plane into the warm, humid, breezy air of Hawaii, you’d think you’d stepped onto the tarmac of heaven. Green leaves sway in the breeze, bright hibiscus blooms around every corner, and the inimitable culture of the island welcomes visitors with open arms.
Surrounded by such beauty, your first thought probably isn’t how the islands formed – yet that might occur to you shortly after leaving the airport. As you wind through green hills and stunningly beautiful rock formations, you may start to wonder just how it all came to be. Read on, and we’ll tell you all about it.
The Hot Spot and Pacific Plate
The first step in understanding the Hawaiian island chain’s birth is understanding plate tectonics. Although the Earth looks static if you stand in one place and look at the horizon, it isn’t. In fact, every piece of land and stretch of the ocean floor – the Earth’s crust – sits atop what we call tectonic plates. These huge pieces of solid rock float upon the sea of magma that lies underneath them called the mantle, which surrounds the molten core of our planet. Because the plates are floating, they naturally move.
We’re not talking a lot of movement, of course. They can move up to 4 inches a year (about the rate of human toenail growth – yuck), and most move more slowly than that. Their slow progress is what causes earthquakes and volcanoes, when they slip or slide against one another, or when one submerges beneath another.
Other times, they move apart, which allows magma to come up from the mantle beneath. When it reaches the surface, it becomes lava, which spills out the sides of volcanoes during eruptions. The lava hardens into the rock that, over time, gets ground into the soil and forms a rich habitat for plants and animals.
Although the Hawaiian islands are made of cooled lava, however, they didn’t form when two tectonic plates collided or moved away from one another. Instead, they are a result of a “hot spot,” an area of the mantle where magma comes much closer to the crust than usual. As plates move over a hot spot, the heat from the magma beneath melts the crust, allowing lava to pour through.
This is how the Hawaiian island chain was formed. As the Pacific Plate moved across the hot spot, the magma beneath poured to the surface of the ocean floor, eventually building up and becoming tall enough to breach the ocean’s surface. And as the plate moved ever onward, multiple additional islands were formed.
This is why the islands show a chain formation rather than a cluster: they were made in succession. The formation called an archipelago, now contains more than a hundred islands and other formations. Today, Hawaii is still a place of active volcanic activity.
The Volcanos of the Big Island
Although “hot spot” makes it sound as though the area over which the Pacific Plate traveled was one small spot from which each island moves on, that’s not the case. The hot spot is, rather, an area of places where the magma is close to the Earth’s crust. As such, several of Hawaii’s islands have conduits to the mantle and are still active.
Others, the more ancient ones, used to have volcanic activity (remember that’s how they formed), but have since gone extinct and will no longer erupt. The hot spot is now too far away to funnel magma to the surface.
Currently, there are only six active volcanoes in the Hawaiian islands, and they are all on or near the Big Island and Maui. The Big Island (also known as the Island of Hawaii) has four of them: Kīlauea, Mauna Loa, Hualālai, and Mauna Kea – though the last is sometimes labeled dormant, as it has not erupted for 4,000 years or so.
Another volcano, Kama‘ehuakanaloa (formerly called Lō‘ihi Seamount) is located about 22 miles southeast of the Big Island, submerged more than 3,000 feet beneath the surface of the ocean. It is the only active submarine volcano in the archipelago.
The last volcano is Haleakalā on Maui, which has not erupted for between 400 and 600 years. Nevertheless, it is still considered active.
Hawaii’s active volcanoes still put on quite the show on the Big Island. A few fast facts:
- Kīlauea is the youngest volcano on the Big Island, erupting nearly nonstop between 1983 and 2018
- About 90 percent of Kīlauea is covered by lava flows younger than 1,100 years
- Kīlauea erupted almost 50 times between 1912 and 2012
- Mauna Loa erupted a dozen times in that same time period
- About 90 percent of Mauna Loa is covered by lava flows younger than 4,000 years
- Hualālai had no eruptions, but a magma intrusion in the century between 1912 and 2012 – which is when the igneous (volcanic) rock cools beneath the surface and pushes its way to the surface in solid form
- The Kona International Airport now sits on lava flows from Hualālai’s 1801 eruption
- About 80 percent of Hualālai is covered by lava flows younger than 5,000 years
- Mauna Kea is the highest volcano in Hawaii and the only one known to have glaciated (become covered in packed ice) during the recent ice ages
All in all, Hawaii is a pretty crazy, lava-filled place even today. It is scientifically fascinating as well, because while all this discussion of lava might lead you to believe there’s only one type, the truth is far more interesting.
Types of Lava
First off, let’s clarify the difference between magma and lava. We already discussed how when magma pushes to the surface, it becomes lava. That’s not because some magical transformation takes place, however, but is instead simply a distinction between when the molten rock is underground (magma) and when it pushes above the surface (lava). When we discuss types of lava, therefore, you can consider them indistinguishable from magma types.
Lavas can be broken down in different ways. In one way, lava is characterized by its mineral composition: basaltic, andesitic, and rhyolitic.
Basaltic lava has lots of iron and magnesium, and not a lot of silica. It forms where mantle material comes up from inside the Earth. Basaltic lava has low viscosity, meaning its relatively runny, so it can travel long distances. It doesn’t tend to blow up violently because it is poor at trapping the gases that cause explosions. As the name suggests, this lava forms basalt when it cools.
Andesitic lava is higher in silica and much thicker – with higher viscosity – so it travels shorter distances. It can result in much stronger eruptions and pyroclastic flows, those that contain lots of rock and debris. This type of lava forms where the crust melts at plate boundaries and one plate is subsumed by another.
The last lava type is rhyolitic. This type of lava is also thick and tends toward explosions, producing lots of ash and pumice in the process. Because it is thick, it tends to form tall volcanoes (as does andesitic lava). It has the highest level of silica, and is also high in potassium and sodium, forming granite when it cools. It also has a high gas content, which increases the explosiveness of its nature. Rhyolitic lava gets squeezed out of volcanoes quite slowly, so it piles up quickly and high, forming domes and cones.
Another way in which lava is broken down is by its flow type. Pahoehoe flows are of a basaltic nature, with low viscosity, so they form a smooth surface on top, though lava can continue to pool beneath the skin, causing it to bulge like toes.
Andesitic lava, as well as the more viscous basaltic lavas, form a’a’, which has a rough-looking surface composed of broken-up blocks known as “clinker.” Pillow lava is when lava pours out beneath the ocean’s surface, cools quickly to form a skin, but continues to fill from within as with pahoehoe, forming pillow shapes that drop off and stack up.
The Hawaiian islands are composed almost entirely of basalt, primarily showcasing pahoehoe and a’a’ lava flow types. With such a similar composition, though, it is amazing how different these many islands are.
The Many Islands of Hawaii
Altogether, the archipelago of Hawaii traverses 1,500 miles of ocean in the North Pacific. While most of us can name only a few of the biggest and most inhabited islands, there is actually 137 total. Eight of those are large enough to merit the name “island,” while several others take the form of ring-shaped atolls of beach surrounding a central lagoon. The rest are small islets and coral reefs.
Only seven of the islands are inhabited, and not all of those are even available for outsiders to visit. Ni’ihau, for instance, only has a population of around a hundred people and is barred from anyone who doesn’t live there unless they have an invitation. The other inhabited islands include Oahu, Maui, Kauai, Molokai, Lanai, and Hawaii, otherwise known as the Big Island.
The Anthropological History of the Islands
Hawaii also has a fascinating, though not always cheerful, anthropological history. Experts estimate that the first settlers arrived from Polynesia around 400 CE, using only the stars as navigational tools. They continued to settle the island in sporadic waves for hundreds of years. By the time Captain James Cook landed on Kaua’i, the islands had been home to a thriving native population for more than a millennia.
Hawaiian culture formed in response to this new home, placing a high priority on living in a community with one another and the land. The Hawaiian relationship to the land is a sacred thing, with native Hawaiians conceiving of themselves as stewards, rather than owners. They refer to themselves as kama’aina, which means “people of the land,” demonstrating their deep attachment to it.
Today, Hawaii is known for arts such as hula, ukulele, and astronomy. The latter is a vocation that it shares with Western scientists, whose views on the use of land for scientific pursuits have a strong colonial nature that native groups are working to overcome. This is characteristic of much of the island, which was colonized by Western nations for hundreds of years, though Native Hawaiians are now beginning to reclaim their land and roots.
The best thing that visitors can do to help them accomplish this is to give their tourist dollars to native peoples rather than large companies, stay respectful of cultural sites, and explore this wonder of the world with the same awe felt by its original inhabitants.
Explore Hawaii’s Geology for Yourself
Now that you know so much about the formation of these beautiful islands, it’s time to put that knowledge to good use. Sure, you could throw out some plate tectonics facts at your next cocktail party, which would certainly impress all the third graders there. (Though they really shouldn’t be at a cocktail party, should they?)
Or you could take your new insights with you to the islands themselves. If you, like most of us, would opt for the latter, we’ve got good news … there are plenty of places in Hawaii where you can experience its storied geology up close.
For instance, you might want to visit Olivine Pools on Maui, where lava flows ending in the sea have created astounding tide pools inside deep holes in the lava platform. The Hana Lava Tube on Maui is an amazing place to see volcanic flow up close, and is less crowded than tubes on the Big Island. Up for a hike? Try the Kīlauea Iki Crater, which is a moderately challenging 2-hour trek that overlooks a crater, as the name suggests. Whatever you do, you’re sure to love these up-close looks at Hawaiian geology.
So, do you feel like an expert in Hawaiian ancient history now? Excellent, because your crash course is complete. It’s time to put it to good use by planning a trip to this gorgeous, thrilling, and historic area today.