(HONOLULU, Hawaii) -- It was supposed to be a bucket-list moment for Dawn Li, an exciting family outing to see where the river of lava from Hawaii's Kilauea volcano spills into the ocean.
But in a flash, the pre-dawn boat tour on Monday for Li, her husband, and their two children turned into a horror show when a so-called "lava bomb" erupted, sending rocks raining on the vessel loaded with photo-snapping tourists.
"I had just said, 'This is like a Jurassic experience.' And my husband said, 'Well, this is on your bucket list,'" Dawn Li told ABC News. "So, we were super excited to see it. It was amazing. But the explosion hit and we all sort of turned simultaneously and my husband kind of leaned over me but we could feel the rocks hitting us."
Piercing screams broke out on the packed tour boat. A rock, or lava bomb, the size of a basketball came crashing through the aluminum roof of the Lava Ocean Tours boat aptly dubbed the "Hot Spot."
"It was literally like an explosion. I've never experienced anything like this," said Li's husband, Dr. Kaming Li, a trauma surgeon. "Just lava flying everywhere, and then this huge explosion and this very large rock hit the boat. When it hit the boat, it crashed through the roof and landed on a person and it was still glowing when it was on the ground."
Dawn Li said she was afraid the rock was so hot it was going to burn through the bottom of the boat. She said the captain and a crew member wrapped it up and shoved it overboard.
After Kilauea first erupted in May, the U.S. Coast Guard restricted boats from coming within 984 feet of where the lava flow dumps into the ocean on the northeast side of Hawaii's Big Island. But some experienced boat operators, including Lava Ocean Tours, have been allowed special permits to take tourists as close as 164 feet from the shoreline.
Greg Valentine, a geology professor at the University of Buffalo's College of Arts and Sciences, told ABC News that the term "lava bomb" refers to the bomb-shaped size of particles hurled in the air generally when they explode from the spout of a volcano. Any projectile larger than 6.4 centimeters in diameter meets the definition of a lava bomb, he said.
He said the thing that was unusual about Monday's lava-bomb event was that it was caused by an interaction of molten lava with sea water.
"Sometimes the lava and the water interact in a certain way and creates a very powerful explosion," Valentine said, adding that some projectiles can travel up to three miles and be as large as a couple of meters in diameter.
Dawn Li said that when the explosion occurred panic spread through the tour boat and everyone rushed to the side furthest from the shoreline.
"It's raining lava rock," Dawn Li said of the moment. "It's hot, it's steamy. My fear was that we were going to capsize because everybody ran to the other side of the boat and you could feel the heat and the steam coming up and the sulfuric fumes."
The water around the boat was "very hot," Kaming Li said.
"We think there was probably a lot of lava underneath the ocean at that place," he said.
Dawn Li added: "You could feel it bubbling, the steam coming up."
Passengers were being pummeled by red-hot rocks. Dawn Li showed ABC News one about the size of a golf ball that hit her.
Her husband began treating peoples' injuries, including a woman who was hit by the basketball-size rock that crashed through the boat's roof. Her femur was fractured, officials said.
"I used to be a trauma surgeon at USC," said Kaming Li. "I've seen a lot of things. This was just crazy."
In the chaos, Dawn Li became separated from her teenage children, Christopher and Erica.
"I started game planning in my mind: The life vests. Who can swim? If we go over, how do we keep ourselves from the shore?" she said. "My kids were separated from me, and so I was just like, 'Oh my God, I've got to get to my kids.'"
Erica Li said the experience went from terrific to terrifying in seconds.
"It was really surreal," she said.
Christopher Li said when the explosion occurred he ducked for cover.
"I immediately got on the ground and covered my neck," Christopher said. "I got hit in the arms."
Both of his legs were also scalded by the downpour of sizzling rocks.
"I got third-degree burns, some second-degree," Christopher said. "But I'm glad to be alive."
Officials said 23 people aboard the boat were injured, but none were in life-threatening condition. Four people were hospitalized at Hilo Medical Center.
"I thought for a moment that this was it, this is how it's going to go," Kaming Li said. "It was a terrifying moment."
Still holding the rock that hit her, Dawn Li said that while she usually collects rocks from wherever she and her family travel, this was a souvenir she didn't plan to keep.
"I'm going to leave it back for the Gods of Pele so that we have no more bad juju," she said as she hurled it into the water.
Copyright © 2018, ABC Radio. All rights reserved.