8. On a Mid-Ocean Ridge - Inside the Rift Valley

Expedition Menu

1. Introduction

2. Theory

3. Formation

4. Evidence

5. Earth's Interior

6. Heat Engine

7. Mid-ocean Ridge

8. On the Ridge

9. Seafloor Spreading

10. Magnetic Field

11. Magnetic History

12. Magnetic Patterns

13. The Plates

14. More on Plates


Here you see a map of the mid-ocean ridge system

Videos modified from
NOAA's ROPOS NeMO 1998 expedition
UCSB Educational Multimedia Visualization Center

The ridge in the Atlantic is called the Mid-Atlantic Ridge, in the Pacific, it is called the East Pacific Rise, and in the Indian Ocean it is either the Southwest Indian Ridge, Central Indian Ridge or Southeast Indian Ridge. There are other smallwer segments of the ridige, such as the Gorda and Juan de Fuca ridges off northern California, Oregon, Washington, and Canada.

If we took a undersea voyage to a ridge, we would find that is was formed of a fairly continuous series of active volcanoes that erupt every 100 to 50,000 years.

A recent cruise by researchers from the Hatfield Center of the National Oceanic and Atmospheric Administration (NOAA) collected the fantastic photographs of the seafloor along a mid-ocean ridge located off Oregon -- we will examine this ridge in future expedition.

The picture on the left shows that the mid-ocean ridge is composed of volcanic rocks, freshly erupted rocks called basalt -- active lava-spouting volcanoes!  

The video on the left shows an underwater hot spring, or a so-called hydrothermal vent, in one of the volcanoes.  The NOAA researchers made a journey to the site of the underwater volcano immediately after it erupted in 1998. 

Fresh volcanic lava on the seafloor


So we first identified ridges in the ocean basins using echo profiler data or multibeam data, then collected rock samples from these features to show that the mid-ocean ridges are chains of underwater volcanoes and inside these volcanoes, lavas are erupted that form new seafloor...the volcanoes also belch hot water, which influences the chemistry of the ocean water (as we will see later in the course). 

The valley on top of the mid-ocean ridge, shown at the left, is called a "rift valley" where the crust of the Earth splits apart, thereby allowing the rise of molten rock from the mantle below that ultimately erupts lavas from volcanoes that form the seafloor at the center of the mid-ocean ridge.

Created By:
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Don Reed
Dept. of Geology
San Jose State University
©Copyright 2008
Last Updated on 
Sept. 22, 2008

   What are mid-ocean ridges?
a. nonvolcanic undersea mountains
b. isolated mountains on the seafloor
c. long chains of active, undersea volcanoes, that sometimes erupt, and that extend from one ocean basin to the next