Fossá Fall EarthCache

Fossá Fall

Waterfalls

A waterfall is a point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf.
Waterfalls can be formed in several ways, but the most common and popularly accepted method of formation is that a river courses over a top layer of resistant bedrock before falling on to the softer rock, which erodes faster, leading to an increasingly high fall.

A typical waterfall combines the following features:

- Significantly increased gradient to at least 100 percent (45 degrees, so the vertical component is larger than the horizontal)
- Decay of the body of water and its partial detachment from the subsurface
- Splash and white water are predominant (colour effect due to light reflections at the air-water interfaces)
- Characteristic noise development
- A microclimate environment of its own

In the case of waterfalls, different sections can be distinguished:

- Beginning of the fall section: possible transition area to the actual waterfall
- Head zone: Area of the waterfall above the fall zone, where the water changes from flowing through shooting into falling
- Falling edge: possible clearly definable point in the head zone of the waterfall, where the water immediately changes from flowing to falling
- Fall zone: Area of the waterfall between the head and impact zone, where the water falls either freely, cascading or shooting (sliding)
- Impact zone: Area of the waterfall below the fall zone, where the falling, shooting or atomized water collides and collects again to form a body of water (characteristics: wetness or high humidity, restricted vegetation)
- Gump: mostly existing stilling basin in the impact zone of the waterfall with strong deep erosion
- Outlet of the fall section - possible transition area to the normal watercourse

List of waterfalls by type:

- Plunge: Water descends vertically, loosing contact with the bedrock surface
- Horsetail: Descending water maintains some contact with bedrock
- Cataract: A large, powerful waterfall
- Multi-step: A series of waterfalls one after another of roughly the same size each which its own sunken plunge pool
- Block: Water descends from a relatively wide stream or river
- Cascade: Water descends a series of rock steps
- Segmented: Distinctly separate flows of water form as it descends
- Tiered: Water drops in a series of distinct steps or falls
- Punchbowl: Water descends in a constricted form and then spreads out in a wider pool
- Fan: Water spreads horizontally as it descends while remaining in contact with bedrock

Scree, rubble, cobbles or pebbles?

Scree is a collection of broken rock fragments at the base of crags, mountain cliffs, volcanoes or valley shoulders that has accumulated through periodic rockfall from adjacent cliff faces. Landforms associated with these materials are often called talus deposits or stony accumulations. Scree is a subcategory of the broader debris class of colluvium: any collection of loose, unconsolidated sediments at the base of hillslopes. The exact definition of scree often overlaps with both talus and colluvium. Colluvium refers to sediments produced by nearly any means and transported by gravity, scree refers to larger blocks and fragments of rock transported downslope.
Rubble is created by physical weathering and erosion, whereby the transport often takes place purely by gravity, but always over very short distances. If the rock fragments are relatively large (dm to m range), one also speaks of block rubble.
Scree (to be rolled) consists of stones, i.e. rock debris that is moved down to the valley during transport by water, landslides, mudslides or other ground movements, and the edges of which were more or less rounded off. Smaller grain sizes are called gravel and sand.
Fluvial rubble occurs near the water and often forms large gravel or gravel banks.
A cobble (cobblestone) is a clast of rock defined on the Udden-Wentworth scale as having a particle size of 64-256 millimeters, larger than a pebble and smaller than a boulder. When occuring in streams, cobbles are likely to be found in mountain valley streambeds that are moderately steep.
A pebble is a clast of rock with a particle size of 4-64 millimeters based on the Udden-Wentworth scale of sedimentology. Pebbles are larger than granules (2-4 mm in diameter) and smaller than cobbles (64-256 mm in diameter). River pebbles of river rock (inland pebbles) are usually found along the shores of large rivers and lakes. These pebbles form as the flowing water washes over rock particles on the bottom and along the shores of the river. The smoothness and colour of river pebbles depends on several factors, such as the composition of the soil of the river banks, the chemical characteristics of the water, and the speed of the current.

Fossá Fall - a special debris situation

The special situation at Fossá Fall is: There are two completely different areas around the plunge pool in terms of deposits. In one area the deposits are created by weathering, erosion and gravity, in the other area by the transport force of the water. Depending on how they were created or how they were transported, the deposits have a completely different appearance. You can, so to speak, learn directly from nature and recognize how different geomorphological changes take place and how different sediments are formed, depending on the deposit situation. Due to this situation, this waterfall offers a site of particular geological interest.

Your task to log the cache:

Answer the following questions via my geocaching profile:

1.) What type of waterfall do you think Fossá Fall is, if you take the informations given in the listing into account?
2.) Take a closer look on the debris around the plunge pool, especially on the stones/rocks just near the waterfall and on the debris at the side of the plunge pool facing the sea - are there any differences between the rocks/stones which are deposited there? Describe the differences in your own words, give me a kind of classification of the debris!
3.) What do you think - why can you observe this debris differences around the plunge pool? Give me a short explanation in your own words!
4.) What do you think - will the seasonal and weather-dependent fluctuating water masses of the waterfall have an influence on the deposits?
5.) Optional: Post a photo with your log, showing you and/or your GPS near the given coordinates in the header!


After you've sent me the message with your answers, feel free to log! Only if there's something wrong, I'll contact you via message!

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