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Erosion of the Mogadishu Coastline

A cache by wildest_monkey Send Message to Owner Message this owner
Hidden : 05/21/2019
1 out of 5
1.5 out of 5

Size: Size:   other (other)

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Geocache Description:

This Earth Cache introduces the geologically interesting and coast of Mogadishu, Somalia. Somalia is blessed with the longest coastline of any African nation and this unique area has been shaped by the powers of the Indian Ocean.

To log this cache you must visit this area, make observations, and then answer task questions based on your observations and from the information below. You should not have to research any further as I have tried to make the information as non-technical as possible.

What gives rocks their colors?

Basic elements found in minerals help give them color. These colors can be affected by a number of factors including light, heat, radiation, and impurities.

Below is a list of some elements and the colors they often produce in minerals:

  • Cobalt: Violet-Red
  • Chromium: Orange-Red
  • Copper: Blue
  • Iron: Red-Brown
  • Manganese: Pink-Purple
  • Nickel: Green
  • Uranium: Yellow

Task 1: Observe the Rocks (Waypoint 1) along the shoreline. Based on the predominate color you see in the rocks, which element appears to be in abundance? How did you come to this conclusion?

How are rocks formed?

Rocks are made by three methods:

  1. Melted and cooled: When volcanic lava cools, whether inside the earth or when it flows to the surface, it becomes solid and forms igneous rock.
  2. Cemented together: When rock fragments, seashells, and chemicals combine with the action of water, they become solid and make sedimentary rock.
  3. Squeezed and heated together: When extreme heat and pressure bake rocks, their structure can completely change and become metamorphic rock.

Task 2: The rocks at Waypoint 1 have a particularly interesting color and texture. Based on the information above and your observations, what kind of rocks are located along the coast here at Waypoint 1? How did you come to this conclusion?

Basic Erosion

The unique features of the Mogadishu Coastline are a result of erosion. Erosion is an action on the surface of the earth (like water movement) that removes rock, soil, and dissolved materials from one location and moves them to another location. These processes are often categorized by the following causes:

  • Water
  • Snow and Ice (glacial)
  • Wind (aeolic)
  • Chemical (corrosion)
  • Gravity (mass movement)
  • Plants and Animals (zoogenic)
  • Humans (anthropogenic)

Coastal Erosion

Coastlines, like the Mogadishu Coast area, are especially vulnerable to erosion. This occurs due to the combined actions of ocean waves and tides, estuaries, storm impacts, chemical processes, and other natural and unnatural forces. Some of these forces are:


This happens when waves break on a cliff face and erode it. The water itself slowly wears down the cliff, while also slamming rock fragments against it, causing yet more erosion.

Hydraulic Action:

When ocean waves strike a cliff face, the force from the water compresses air inside cracks in the cliff. The resulting air pressure causes the cracks to grow and rocks to splinter. The splintered rock can add to the erosion process (attrition).


Attrition occurs when waves cause loose pieces of rock debris to collide with each other. They grind and chip each other, progressively becoming smaller, smoother and rounder. This is similar to sandblasting or using sandpaper.

Corrosion (solution):

Corrosion, or chemical erosion, takes place when the sea's salt, acids, and other chemicals dissolve some types of rocks, especially those with higher pH levels like chalk and limestone. Wave action increases the rate of erosion by removing the dissolved material.

Task 3: Observe the the surface of the rocks in Waypoint 1, as well as the area around them (Posted Coordinates). Take into account the materials that the rocks are made of as described in Task 2, as well as this location. Which coastal erosion process do you think was responsible for their unique surface, and why?

Task 4:Waypoint 2 seems to be completely different geologically from Waypoint 1 and the Posted Coordinates. Based on your observations of the shape of the coastline at Waypoint 1 and the Posted Coordinates, and the shape of the coastline at Waypoint 2, which coastal erosion process occurred at Waypoint 2.? Why do you think they differ?

Task 5: At Waypoint 1 feel the Rocks. Now, pick up some sand at your feet. (Near Posted Coordinates and Waypoint 2). Examine and feel the sand. Compare the Rocks and the sand and answer the following questions:

  • Is the color of the sand more similar to or more different from the color of the Rocks?
  • How is the texture of the Rocks different from the texture of the sand?
  • What erosion process(es) do you think contributed to the difference in textures, and why?

Task 6: (Optional) Post a picture of yourself with your GPS somewhere in Mogadishu.

You may log your find as soon as you send me your answers, but you must visit the site and complete the tasks. Please uphold the integrity of this game and do not log this cache unless you actually visit this Earth Cache. I hope you enjoy your visit to the coast of Mogadishu here in Somalia!

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