The Big Island - 4028 square miles
Maui - 727 square miles.
O’ahu - 597 square miles
Kaua’i - 552 square miles
Moloka’i - 140 square miles
I know that the Hawaiian Islands are the newest creation in the Hawaiian–Emperor seamount chain, formed as the Pacific plate slides over a hot spot. As volcanoes in this chain are no longer added to, erosion continues to wear them away. If you ain’t growing, you’re shrinking.
Are there any signs any of the other islands were once as large as the Big Island is now? With 5 volcanoes within that 4028 square miles, and another one just off shore, that seems like a close cluster of volcanoes, making me wonder if the plate movement is slowing down, the hot spot spreading out, or if the other islands have just eroded that fast.
It’s going to be hard to know for sure how big the eroded islands may have been, but a quick look at the underwater topography suggests some of the islands in the Northwest Hawaiian Islands could have been close to the size of the Big Island.
During the ice age, Maui Nui was bigger than the Big Island:
1.2 million years ago, Maui Nui was 14,600 square kilometres (5,600 sq mi), 40% larger than the present-day island of Hawaiʻi.
Check out this Wikipedia page on Maui Nui. What is now Maui, Lana’i, Moloka’i and Kaho’olawe was once a single island, made up of multiple volcanoes, bigger than Hawai’i is today.
Also check out the underwater map, you can see much of what has eroded. And due north of Moloka’i you can see the debris left over from a massive landslide that chopped the island in half and left it with magnificent sea cliffs.
Thanks for those links. It does look like in 500,000 years or so, the Big Island will be several smaller islands (volcano summits). Now’s the time to buy that future family beach front land on Mauna Loa.
Erosion below wave depth is minimal compared to open air weathering and wave erosion. You can see this if you zoom in on the chain in Google maps and use the satellite view. The older volcanoes that once stood above sea level are shaved down to shallows, but it’s quite obvious there were once substantial islands there from the flat topped sea mounts you still see.
Here is a slide show history of Oahu’s geology. Slide 5 shows the extent of the Wai’anae and Ko’olau volcanoes before the slump (Wai’anae) and great Nuuanu landslide that decimated the Ko’0lau volcano. Nuuanu landslide is one of largest in history with tsunamis reaching near 1000’ on nearby islands and up to 600’ on the Pacific coast exposures. Other good information although not without some proofreading errors.
Nuuanu landslide youtube animation and wave propagation.
The last portion is a chilling mention that the current east rift zone eruption on Hawaii is the probable next mega-tsunami location.