Ngardmau Waterfall Introduction
Ngardmau Waterfall is one of the most beautiful and unexpected places in Palau. When most travelers think about Palau they think about the Jellyfish Lake, the Rock Islands and the multitude of famous scuba diving spots like the Blue Corner. However, Palau has many hidden treasures on the mainland too. Ngardmau Falls is the Tallest waterfall in Micronesia (not the country, the chain of islands). It flows from Palau's tallest peak 217m-high Mt Ngerchelchuus. It can be accessed on foot and takes about 20-30 minutes to hike there. I recommend wearing shoes with a grip that can get wet as much of the hike is through a river. Also, soaking in the water at the base of the waterfall is not to be missed. It also isn't a crowded attraction and you might even get luck and be the only one there. When you are driving to the waterfall make sure that you park at the waypoint provided as mapping programs don't seem to know where the trail head is located. Also, like the rest of Palau, there is a fee to access this spot. When I was there it was $10 per person to access.
Geology of Palau Overview
The country of Palau is mostly known for it's amazing mushroom shaped limestone formations in the rock islands, but the islands were first created by gigantic volcanic explosions. This in turn created a great place for corals to start growing and over millions of years, turn to limestone.
The main island of Babeldaob where many of the people of Palau live still shows the evidence of this ancient extinct volcano. Between 50 and 27 million years ago the Kyushu-Palau ridge (underwater) was a very active volcanic arch that was formed by the subducting Pacific Plate. Specifically, Palau's volcanoes were active 37.7 and 20.1 million years ago. Over much of this volcanic rock limestones formed. Later, rotation of the Philippine Sea Plate and its convergent boundary with the Caroline Plate led to uplift of the islands you see now. The islands are still riding by about 0.5mm each year.
Ngardmau Falls Geology
As you are on your hike toward Ngardmau Falls, you will notice that the rock on the hike is different than the rock that you see in Koror. Koror and the Rock Islands mostly consist of limestone created from the ancient reefs that grew atop the ancient volcano that created Babeldaob.
The rock that you are seeing is volcanic in origin and and was formed from a large explosion several million years ago. This rock is called Tuff. Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. The tuff often has chunks of tephra embedded inside. Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. The distribution of tephra following an eruption usually involves the largest boulders falling to the ground quickest, therefore closest to the vent, while smaller fragments travel further – ash can often travel for thousands of miles, even circumglobal, as it can stay in the stratosphere for days to weeks following an eruption. Once clasts have fallen to the ground, they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff.
Tuff Classification
Welded Tuff is a pyroclastic rock, of any origin, that was sufficiently hot at the time of deposition to weld together. Welded tuffs can be of fallout origin, or deposited from pyroclastic density currents. During welding, the glass shards and pumice fragments adhere together (necking at point contacts), deform, and compact together, resulting in a layered or banded structure.
Rhyolitic tuffs contain pumiceous, glassy fragments and small scoriae with quartz, alkali feldspar, biotite, etc. The broken pumice is clear and isotropic, and very small particles commonly have crescentic, sickle-shaped, or biconcave outlines, showing that they are produced by the shattering of a vesicular glass, sometimes described as ash-structure.
Trachyte tuff contain little or no quartz, but much sanidine or anorthoclase and sometimes oligoclase feldspar, with occasional biotite, augite, and hornblende. In weathering, they often change to soft red or yellow clay-stones, rich in kaolin with secondary quartz.
Andesitic tuffs are fairly common. In color, they are red or brown; their scoriae fragments are of all sizes from huge blocks down to minute granular dust. The cavities are filled with many secondary minerals, such as calcite, chlorite, quartz, epidote, or chalcedony; in microscopic sections, though, the nature of the original lava can nearly always be made out from the shapes and properties of the little crystals which occur in the decomposed glassy base. Even in the smallest details, these ancient tuffs have a complete resemblance to modern ash beds.
Basaltic tuffs are also fairly common. They are black, dark green, or red in colour; vary greatly in coarseness, some being full of round spongy bombs a foot or more in diameter; and being often submarine, may contain shale, sandstone, grit, and other sedimentary material, and are occasionally fossiliferous.
Ultramafic tuffs are extremely rare; their characteristic is the abundance of olivine or serpentine and the scarcity or absence of feldspar and quartz. The principal rock is a dark bluish-green, serpentine-rich breccia (blue-ground) which when thoroughly oxidized and weathered becomes a friable brown or yellow mass (the "yellow-ground").
Logging Requirements
1. What kind of tuff do you think is present at the waterfall?
2. Explain why you think this.
3. Do you think you are far from the site of the ancient volcanic explosion?
4. Explain why you think this.
5. Take a picture of your GPS or something that identifies your connection to geocaching at the cache zone and upload it with your log. (This is required to log this geocache)
6. Please send the answers to me by message on my profile. You may log this cache as “Found.” (If the answers are not correct I will contact you.)
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