BIOL 331

Lecture 1

The Oceans

Significance of the Hypsographic Curve

• Earth has two distinctly different levels
• Extreme height (8848 m), Extreme depth (11,035 m)
• Depth of ocean if all land were dumped in: 2430 m
• Compared to earth's diameter (6370 m) these contrasts are minute.

Continents and Continental Margins

• Continental Shelf: Submerged upper part of continental margin.
• Shelf Break: Where continental shelf abruptly drops off (~130 m, up to 500 m off Antarctica & in Arctic).
• Continental Slope: Steep downslope up to 2-3 km.
• Submarine Canyons: Cut through continental shelves and slopes.
• Continental Rises: At base of Continental slopes & slope gently to deep-sea floor.

Midocean Ridges

• Most conspicuous feature.
• Rift Valley: Forms between rugged peaks of midocean ridges. 125-50 km wide and 1-2 km deep in Atlantic.
• Fracture Zones: Intersect midocean ridges and offset them.

Examples of Fracture Zones:

• The Mendocino Fracture Zone comes to land at Cape Mendocino and becomes the San Andreas Fault.
• The Romanche Fracture Zone is world's largest and offsets the Atlantic Ridge by 950 km near the equator.

The Deep Ocean Floor

• Abyssal Plains: Flattest places on earth, deeper than 4 km, near continents.
• Abyssal Hills: Prominent feature of deep ocean, less than 1 km (often 200 m) above sea floor.

Trenches

• Often 3-4 km deeper than the surrounding ocean floor.
• Trenches border much of the Pacific.
• Associated with active volcanoes and earthquakes.
• Mariana Trench SE of Japan is deepest at 11,035 m.

Volcanoes

• Common in midoceanic ridges where they form pillow lavas.
• Shallow water volcanoes often more explosive and form lots of ash.
• Island formation by volcanoes produce island arcs.
• Shield volcanoes in the middle of ocean basins can also produce islands (Hawaii).

Oceanic Plateaus

• Isolated parts of ocean floor that stand 1+ km above the
• surrounding ocean floor.
• Some are fragments of continental blocks.
• Others are associated with volcanoes.

Comparisons Among the Oceans

Links to Ocean Maps

• Southern Ocean Floor Topography

• Crustal Boundaries, Earthquake Centers, Ring of Fire

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