Welcome to Maniniholo Dry Cave!
✔️ This is a protected natural site – please respect the land and leave no trace.
✔️ The cave is easily accessible, but bring a flashlight if you want to explore deeper inside.
✔️ Be mindful of rockfall hazards and uneven terrain.
LOGGING REQUIREMENTS: To claim this EarthCache 
, you must first visit the posted coordinates and then Send Answers via the geocaching.com Message Center to the following questions based on your observations and the information provided in the short Earthcache Lesson below:
- Examine the cave walls. Describe any evidence you see of evidence of past wave erosion, such as smoothed rock surfaces or scalloped patterns.
- Observe the floor. Does the floor look as aged as the ceiling? Has life had time to grow on the floor as it has on the ceiling? What does this tell you about the ongoing erosion processes?
- Verify visit. Look at the sign across the street. What is not allowed in Haena Beach Park? (one word)
- Bonus Photo (Optional): Take a picture of yourself or your GPS near the cave entrance.
EARTHCACHE LESSON: Maniniholo Dry Cave is a prime example of a relict sea cave, a geological formation shaped by coastal and tectonic forces over thousands of years. It offers a unique opportunity to study the processes of wave erosion, sea-level fluctuations, and tectonic uplift, all of which have contributed to its present-day form. This EarthCache explores the geological processes that led to its creation and the forces that continue to shape it today.
The cave is situated near Haena State Park, close to the base of Makana Mountain (also known as Bali Hai). While it is now a dry cave, its origins tell the story of a dynamic and ever-changing coastline. Understanding its formation provides insight into the geological history of Kauai, the oldest of the Hawaiian Islands.
A simple classification of caves includes four main types:
- Solution caves are formed in carbonate and sulfate rocks such as limestone, dolomite, marble, and gypsum by the action of slowly moving ground water that dissolves the rock to form tunnels, irregular passages, and even large caverns along joints and bedding planes. Most of the caves in the world as well as the largest are of this type.
- Lava caves are tunnels or tubes in lava formed when the outer surface of a lava flow cools and hardens while the molten lava within continues to flow and eventually drains out through the newly formed tube.
- Sea caves are formed by the constant action of waves which attacks the weaker portions of rocks lining the shores of oceans and large lakes. Such caves testify to the enormous pressures exerted by waves and to the corrosive power of wave-carried sand and gravel.
- Glacier caves are formed by melt water which excavates drainage tunnels through the ice.
Geological Formation of Maniniholo Dry, Sea Cave
Sea caves you might guess would be wet, but Maniniholo is dry and easy to explore without any special gear. Here is why…
1. Wave Erosion and Coastal Carving
Initially, Maniniholo Dry Cave was formed through mechanic
al erosion as powerful ocean waves battered the volcanic rock along Kauai’s northern coastline. Over time, water exploited natural fractures and weaknesses in the basalt, gradually hollowing out a cave. This process was accelerated by the presence of air pockets and gas vesicles within the volcanic rock, which made some areas more susceptible to erosion.
The erosional force of hydraulic action—where waves force air and water into rock cracks—played a significant role in expanding the cave. Additionally, abrasion from sand and rock particles carried by waves helped smooth out the walls of the cave. These forces collectively shaped the rounded, scalloped formations seen on the cave walls today.
2. Tectonic Uplift and the Emergence of a Dry Cave
Over millions of years, the Hawaiian Islands have been gradually moving northwe
st due to the Pacific Plate’s motion over the Hawaiian hotspot. As Kauai is the oldest of the main islands, it has undergone the most significant amount of tectonic uplift.
As the island rose due to crustal movements, the cave was slowly lifted above sea level, transforming it from an active sea cave into a dry cave. This uplift process is still ongoing, meaning that in thousands of years, Kauai’s coastline may look entirely different.
3. Sea-Level Fluctuations and Climate Effects
Throughout Earth’s history, global sea levels have fluctuated due to glacial and interglacial periods. During ice ages, large amounts of water were trapped in glaciers, lowering sea levels. During warmer interglacial periods, melting ice caused sea levels to rise, submerging coastal landforms like Maniniholo Cave.
Approximately 15,000 years ago, toward the end of the last Ice Age, sea levels were significantly lower. As the ice melted, rising ocean waters helped carve the cave deeper before eventually receding again. Today, the cave stands as a remnant of a coastline that once extended further inland.
4. The Impact of Tsunamis and Storm Events
Large tsunamis and storms have played a role in reshaping the cave. One significant event was the 1946 tsunami, which caused major structural changes to the cave entrance. The massive wave force washed away debris, widened the entrance, and contributed to the cave’s modern-day shape.
Because of its coastal location, Maniniholo Cave continues to be affected by extreme weather events, wind erosion, and occasional heavy rainfall, which can cause further rockfalls and sediment deposition.
5. Rock Composition and Structural Features
The cave is made of porous basalt, which originated from lava flows that once covered the region. The basalt is full of small vesicles (gas bubbles), making some areas more prone to differential erosion, where softer materials wear away faster than denser rock.
Observing the walls, you’ll notice striations, cracks, and pockets of varying hardness—all indicators of how erosion has shaped the cave over time. The ceiling of the cave has weakened due to continuous weathering and gravitational stress, leading to small collapses that further contribute to its evolving form.
6. Cave Ceiling Collapse and Ongoing Erosion
As with many sea caves, the ceiling of Maniniholo Cave has been affected by subaerial weathering—a combination of physical and chemical erosion processes that occur above the waterline. Rainwater seepage through porous basalt has contributed to mineral leaching, weakening the rock and making it more susceptible to collapse over time.
Because of these factors, you may notice piles of fallen rock on the cave floor, evidence that the cave is still undergoing slow geological changes.
Sources:
https://www.kauai.com/wet-and-dry-caves
https://www.usgs.gov/publications/geology-caves
https://en.wikipedia.org/wiki/Sea_cave
https://www.nps.gov/subjects/caves/sea-or-littoral-caves.htm