Hawaii Most Beautiful Bay Volcanic Origin in the World Hanauma Crater to Bay - Shawn Matsunaga

Summary

Sean Matsunaga presents an educational journey into Hanauma Bay's geological history, formed by volcanic eruptions 32,000 years ago. The bay, composed of hardened volcanic ash and coral, showcases diverse rock types and a vibrant ecosystem. Despite damage from a 1956 cable installation, the reef has recovered, becoming a haven for marine life. The script also highlights two sand restoration projects and the importance of parrotfish in reef health and sand production.

Takeaways

• 🌋 Hanauma Bay was formed 32,000 years ago from molten ash and debris from underwater volcanic explosions.
• 🏔 The bay's unique geological composition includes basalt, coral, and tuff, which are visible in the surrounding walls.
• 🧱 Basalt is a heavy, fine-grained rock prized by Hawaiians for tool and weapon making, while coral contributes to the formation of limestone.
• 🌊 The 1956 construction of an undersea telephone cable caused significant damage to the reef, but also created new habitats for marine life.
• 🏖 Two sand restoration projects in 1970 and 1987 aimed to rebuild the beach and restore the reef after the 1956 damage.
• 🐟 The artificial swimming area created post-1956 now supports species not typically found in sandy-bottom lagoons.
• 🏞 The north end of the bay features fine sand with basalt, coral, and sea creature shells, while the south end has coarser sand with larger sediments.
• 🏝 The far end of the bay resembles a deserted island with large rock and coral chunks, driftwood, and other debris.
• 🌊 An oil-like substance was observed on the water's surface, indicating ongoing environmental challenges.
• 🐠 Parrotfish, which have strong beaks for eating coral and algae, are significant contributors to sand production, generating over a ton of sand per year.
• 🌱 Despite initial concerns, parrotfish are now recognized as beneficial to reef health by preventing algae overgrowth.

Q & A

What geological event led to the formation of Hanauma Bay?

Hanauma Bay was formed due to a series of violent explosions 32,000 years ago when a volcanic vent opened underwater, causing hydromagmatic blasts that blew up steam, hot gases, coral rock, and fine ash. The ash chemically cemented together over time to create the bay.

What types of rocks can be found at Hanauma Bay?

At Hanauma Bay, you can find basalt, lava rock, and tuff. Basalt is the most common volcanic rock in Hawaii, while tuff is the volcanic ash that hardened due to a natural cementing process.

How did the dredging in 1956 affect Hanauma Bay's reef?

The dredging in 1956 caused significant damage to Hanauma Bay's reef by blowing a 200-foot wide strip through it, removing tons of coral rocks, and oiling the water, which led to the destruction of the central portion of the fringing reef.

What positive outcome resulted from the 1956 dredging?

The dredging in 1956 created a new biological zone inside the reef. The loose rubble left by the blasting became a habitat for a host of small invertebrates and fishes, providing them with ample living space and improving circulation inside the reef.

What were the two sand restoration projects at Hanauma Bay?

The two sand restoration projects were in 1970 and 1987. In 1970, sand was imported to build a wave barrier on the reef crests to close the 1956 cable trench and restore the beach. In 1987, 3,500 cubic yards of sand were imported from Kahuku, Oahu to restore the beach due to beach erosion.

What is the texture of the sand like at Hanauma Bay?

The sand at Hanauma Bay is very fine with grains of basalt, coral, and shells of various sea creatures. However, the texture changes to more coarse as you move to the other side of the bay, with larger pieces of basalt, coral, and other sediments.

What debris can be found along the shoreline of Hanauma Bay?

Debris found along the shoreline of Hanauma Bay includes strands of rope, plastic, lanyards woven into various types of debris, half-eaten coconuts, and other green waste.

What role do parrotfish play in the sand formation at Hanauma Bay?

Parrotfish are responsible for creating sand by consuming coral and excreting sand. One large parrotfish can generate over a ton of sand per year, and the entire species is responsible for the output of over a billion tons of sand per year.

How does the presence of parrotfish affect the health of the reef at Hanauma Bay?

Parrotfish promote a healthy reef by preventing algae from smothering it. Although it was once thought that parrotfish were destroying the reefs, it was later found that their activities actually help maintain the reef's health.

What other locations are known for their beaches and parrotfish populations?

Parrotfish can be found in other tropical places known for their beaches such as the Bahamas, throughout the Caribbean, Florida, and the eastern and western boundaries of the Gulf of Mexico.