Volcanoes, Oceans, and Seawater Composition: Key Concepts

Chapter 7: Volcanoes & Chapter 10: Restless Ocean

Volcanic Eruptions

Eruptions can be explosive (gases escape from melt) or quiescent ("Hawaiian" very fluid basaltic lavas).

Volcano Types

Volcano types include shield volcanoes (accumulation of fluid basaltic lavas, exhibit shape of broad domed structure) and composite volcanoes (large, nearly symmetrical, persistent eruption of viscous lava, conical shape).

Viscosity: Determined by temperature, composition, and amount of dissolved gases – how resistant to flow.

Pyroclastics: Pulverized rock, lava, and glass fragments ejected from vent.

Chapter 9: Oceans

Ocean Features

Continental Shelf: The gently sloping submerged portion of the continental margin that extends from the shoreline to the continental slope.

Continental Slope: The steep gradient that leads to the deep ocean floor and marks the seaward edge of the continental shelf.

Abyssal Plain: A very level area of the deep-ocean floor, usually lying at the foot of the continental rise.

Mid-Ocean Ridge: A continuous elevated zone on the floor of all the major ocean basins and varying in width from 500 to 5000 km. The rifts at the crests of these ridges represent divergent plate boundaries. Also known as the oceanic ridge.

Seawater Composition

Composition of Seawater: Salinity is the proportion of dissolved salts to pure water. Average salinity ranges from 35 percent to 37 percent. Principle elements are chlorine and sodium. The primary source of the elements for the elements in sea salt are chemical weathering of rocks on the continents and volcanic outgassing on the ocean floor.

Variations in seawater salinity are primarily caused by changing water content, e.g., adding large amounts of freshwater to seawater, increased precipitation, runoff from land, iceberg melting, and sea ice melting. Evaporation of fresh water also affects salinity.

Ocean Dynamics

Coriolis Effect: The deflective force of Earth's rotation on all free-moving objects, including the atmosphere and oceans. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Upwelling: The rising of cold water from deeper layers to replace surface water that has been moved away.

Tides: Periodic change in elevation of the oceans surfaces.

Waves: Wave height is the vertical distance between the trough and crest of a wave. Wave period is the time interval between the passage of successive crests at a point.

Ocean Bathymetry

Ocean Bathymetry: Bathymetry is the measurement of ocean depths and the charting of the shape of the ocean floor. Sonar (navigation and ranging) echo sounders are the first type of sonar technology that transmits a sound wave into water. Satellites can also be used using radar pulses from space.