# The Shape of the Seafloor

Part of the Oceanography Merit Badge Digital Resource Guide: [Introduction & Overview](https://merit-badge.university/merit-badges/oceanography/guide/index.md)

*4. Underwater Landscapes*

> **4.** Draw a cross-section of underwater topography. Name and put on your drawing the following: seamount, guyot, rift valley, canyon, trench, and oceanic ridge. Compare the depths in the oceans with the heights of mountains on land. Show what is meant by:

This requirement starts with a drawing because oceanography becomes much easier once you can picture the seafloor. Your cross-section should show the coast, shallow continental edge, steep drop-off, broad deep basin, and major underwater mountains and valleys.

[Diagram of Sea Floor (website)](https://www.visualdictionaryonline.com/earth/geology/ocean-floor.php): A labeled seafloor diagram that helps you place each underwater feature in the right relative position.

Video: [How Deep Does the Ocean Go? (video)](https://youtu.be/mAwfTahzbtw)

Video: [How Deep the Ocean REALLY Is (video)](https://youtube.com/shorts/DZ9v54D4mZ8?si=l4pnMMCRDzgxQOpF)

![Cross-section of the seafloor labeled with continental shelf, continental slope, abyssal plain, seamount, guyot, ridge, rift valley, canyon, and trench](https://ik.imagekit.io/doulacoop/tr:w-800/mbu-assets/merit-badges/oceanography/guide/ocean-floor-cross-section?v=14768b4f)

## Building Your Cross-Section

A strong drawing does not need to look artistic. It needs to be clear.

Start at land and move outward:

1. coastline and shallow nearshore water
2. **continental shelf**
3. **continental slope**
4. deep basin with an **abyssal plain**
5. extra features such as trench, ridge, rift valley, seamount, guyot, and canyon

A **seamount** is an underwater mountain. A **guyot** is a flat-topped seamount, usually worn down near sea level long ago and then carried lower. An **oceanic ridge** is a long underwater mountain chain, often with a central **rift valley** where tectonic plates pull apart. A **submarine canyon** cuts into the continental margin. A **trench** is a very deep, narrow depression where one plate sinks below another.

## Requirement 4a: Continental Shelf

> **4a.** Show what is meant by Continental shelf.

The **continental shelf** is the shallow, gently sloping submerged edge of a continent. Even though it is underwater, it is still part of the continent itself. Shelves are often rich fishing areas because sunlight reaches the water, nutrients can mix in, and life is abundant.

### What to show on your drawing

Draw the continental shelf as the broad, shallow platform just offshore before the steep drop begins.

## Requirement 4b: Continental Slope

> **4b.** Show what is meant by Continental slope.

The **continental slope** is the steeper region beyond the shelf. It marks the transition from shallow continental edge to deep ocean basin. On your drawing, it should look like the part where the seafloor angles downward much more sharply.

### What to show on your drawing

Make the slope noticeably steeper than the shelf so the difference is easy to see.

## Requirement 4c: Abyssal Plain

> **4c.** Show what is meant by Abyssal plain.

The **abyssal plain** is a broad, deep, relatively flat part of the ocean floor. "Flat" is relative — it is still deep, dark, and huge — but compared with mountains, ridges, and trenches, it is one of the smoothest large regions on Earth.

### What to show on your drawing

After the continental slope, draw a wide flatter section in the deep ocean basin.

**Feature Placement Guide** — Where each major seafloor feature usually belongs

- [ ] **Shelf**: shallow and near the coast.
- [ ] **Slope**: steep drop beyond the shelf.
- [ ] **Abyssal plain**: broad deep basin.
- [ ] **Canyon**: cut into the shelf or slope.
- [ ] **Oceanic ridge**: raised mountain chain in the deep ocean.
- [ ] **Rift valley**: depression running along some ridges.
- [ ] **Trench**: deepest narrow low point.

## Comparing Ocean Depths and Mountain Heights

This part surprises many people. The tallest mountains on land and the deepest trenches in the ocean are in the same general scale. Mount Everest rises about 29,000 feet above sea level. The Mariana Trench reaches deeper than 36,000 feet below sea level. That means parts of the ocean are deeper than Everest is tall.

> **Did You Know?**
>
> If Mount Everest were dropped into the deepest part of the Mariana Trench, its summit would still be underwater.

> **Tip**
>
> When you show your drawing to your counselor, point from left to right and explain the story of the seafloor in order. That makes the labeled features easier to remember.

Next you will shift from landforms to the chemistry of seawater itself.

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- Previous: [Waves, Breakers & Rip Currents](https://merit-badge.university/merit-badges/oceanography/guide/req3/index.md)
- Next: [Seawater Chemistry](https://merit-badge.university/merit-badges/oceanography/guide/req5/index.md)