Wonder if the tunnels are old lava tubes. When lava flows underground it makes tunnels (there's a better scientific explanation). I've been in one on the Big Island. They could be easily expanded or connected.
I think the sides are, since it is a tube through lava. There are stories of the tops collapsing when people have walked across the ground above the tunnel. One story tells of a man that disappeared, his body was found months later in a lava tube under his property. He fell about 30 feet.
The one I went in was stable at the time. I'm not an expert. I believe the lava cut's the tunnel. Many or all go to the ocean. I went in the one in the first link but not very far because it's very wet inside and uneven ground. I'm a klutz by nature and didn't want to be messed up on vacation. The ones on National parks have lights. Anywhere there is or has been an active volcano should have lava tunnels. All of Hawaii islands are old volcanos. I think volcanoes in Hawaii are a little different in appearance than say Mount St Helen's that's a mountain. Kīlauea Volcano on the big island has a huge flat area you can walk on. It's in mountainous region.
I think Maui has an active volcano, not sure. I remember hearing about the submarine tour that you see lava flowing in ocean. I took the submarine on Oahu (no volcanic activity) it was natural reefs and fish.
Edit: my original statement a stability after 808RosY3 comment.
Wonder if the tunnels are old lava tubes. When lava flows underground it makes tunnels (there's a better scientific explanation). I've been in one on the Big Island. They could be easily expanded or connected.
I think the sides are, since it is a tube through lava. There are stories of the tops collapsing when people have walked across the ground above the tunnel. One story tells of a man that disappeared, his body was found months later in a lava tube under his property. He fell about 30 feet.
https://www.nps.gov/places/nahuku.htm
The one I went in was stable at the time. I'm not an expert. I believe the lava cut's the tunnel. Many or all go to the ocean. I went in the one in the first link but not very far because it's very wet inside and uneven ground. I'm a klutz by nature and didn't want to be messed up on vacation. The ones on National parks have lights. Anywhere there is or has been an active volcano should have lava tunnels. All of Hawaii islands are old volcanos. I think volcanoes in Hawaii are a little different in appearance than say Mount St Helen's that's a mountain. Kīlauea Volcano on the big island has a huge flat area you can walk on. It's in mountainous region.
Kīlauea https://www.nps.gov/havo/index.htm
https://www.lovebigisland.com/activities-to-do/lava-tubes/
Maui https://www.cntraveler.com/activities/maui/hana-lava-tube
I think Maui has an active volcano, not sure. I remember hearing about the submarine tour that you see lava flowing in ocean. I took the submarine on Oahu (no volcanic activity) it was natural reefs and fish.
Edit: my original statement a stability after 808RosY3 comment.
You make a very good point. Thanks for pointing out my era about the lava tube stability.