<p>I think the <a href="https://pubs.usgs.gov/gip/dynamic/developing.html" rel="nofollow noreferrer">U.S. Geological Survey</a> has the gist of your answer -- prior to the mid-1900s, there wasn't enough seismological data to draw any conclusions:</p>

<blockquote>
  <p>During the 20th century, improvements in seismic instrumentation and
  greater use of earthquake-recording instruments (seismographs)
  worldwide enabled scientists to learn that earthquakes tend to be
  concentrated in certain areas, most notably along the oceanic trenches
  and spreading ridges. By the late 1920s, seismologists were beginning
  to identify several prominent earthquake zones parallel to the
  trenches that typically were inclined 40-60° from the horizontal and
  extended several hundred kilometers into the Earth. These zones later
  became known as Wadati-Benioff zones, or simply Benioff zones, in
  honor of the seismologists who first recognized them, Kiyoo Wadati of
  Japan and Hugo Benioff of the United States. The study of global
  seismicity greatly advanced in the 1960s with the establishment of the
  Worldwide Standardized Seismograph Network (WWSSN) to monitor the
  compliance of the 1963 treaty banning above-ground testing of nuclear
  weapons. The much-improved data from the WWSSN instruments allowed
  seismologists to map precisely the zones of earthquake concentration
  worldwide.</p>
</blockquote>

<p>This evidence led to <a href="https://www.britannica.com/science/seafloor-spreading-hypothesis" rel="nofollow noreferrer">geophysicist Harry H. Hess hypothesizing seafloor spreading in 1960</a>. Researchers from Scripps Institution of Oceanography and Woods Hole Oceanographic Institute, among others, would spend years gathering evidence from the world's seafloors to test that theory, using oceanographic vessels, equipment, and analytical techniques that were not available in previous decades.</p>

CC BY-SA 3.0
2017-02-13T20:58:33.160Z
2017-02-13T20:58:33.160Z
jeffronicus
<p>If it weren't for WW2 and the search for German submarines, the discovery of mid-ocean ridges might have waited until satellite based gravimetric mapping in the 1980s. It was the use of fine magnetometers (if I remember correctly) used to detect submarines that discovered the banding of magnetic stripes on the Atlantic ocean floor, followed by it's mirror image after a certain mid-point in the ocean basin. When superposed with bathymetric maps, it was further discovered that these magnetic stripes had their counterpoint in the same topographic region on the other side of a high point.</p>

<p>The analysis of thousands of these ship transect records (released by the Navy following WW2)  led to the creation of partial ocean floor maps revealed very long parallel strips of rocks containing magnetic reversals reflected in mirror symmetry on the opposite of a mid-ocean rise. Ocean drilling then confirmed that only a spreading volcanic ridge, spewing magma over tens of millions of years could create such features. Following that, precise seismological mapping also confirmed this developing "theory" of plate tectonics, that laid to rest Alfred Wegener's model.</p>

<p>These were heady times for the geologic community in the 60s and early 70s! All thanks to the Navy and WW2!</p>

CC BY-SA 3.0
2017-02-13T20:47:21.130Z
This US Geological Survey page elaborates on that point (https://pubs.usgs.gov/gip/dynamic/developing.html): Beginning in the 1950s, scientists, using magnetic instruments (magnetometers) adapted from airborne devices developed during World War II to detect submarines, began recognizing odd magnetic variations across the ocean floor. This finding, though unexpected, was not entirely surprising because it was known that basalt -- the iron-rich, volcanic rock making up the ocean floor-- contains a strongly magnetic mineral (magnetite) and can locally distort compass readings.
jeffronicus
CC BY-SA 3.0
2017-02-14T15:15:59.817Z
They were actually looking for Russian submarines during the Cold War but otherwise this is a great answer.
bon
CC BY-SA 3.0
2017-02-13T20:33:17.187Z
2017-02-13T20:33:17.187Z
Knob Scratcher
<p>I just read <a href="https://www.nytimes.com/2016/01/12/science/midocean-ridges-volcano-underwater.html">this article</a> and was astonished to see the following:</p>

<blockquote>
  <p>Oceanographers stumbled on [the mid-oceanic ridges'] volcanic nature in 1973.</p>
</blockquote>

<p>What I find surprising is how <em>recent</em> that is.</p>

<p>Considering that</p>

<ul>
<li>the <a href="http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=aa77">history of geology</a> in general goes back at least 3 or 4 centuries</li>
<li>the study of plate tectonics <a href="http://www.ucmp.berkeley.edu/geology/techist.html">goes back to 1912</a> (even though it took a few more decades to gain wide acceptance)</li>
<li>oceanic ridges were known at least <a href="https://en.wikipedia.org/wiki/Mid-Atlantic_Ridge">as early as 1872</a></li>
<li>the correlation between <a href="http://www.geology.sdsu.edu/how_volcanoes_work/Volcano_tectonic.html">seismic activity and volcanoes</a> has been known for some time (I don't know exactly how long, but <em>certainly</em> the Romans felt the ground shaking when Vesuvius' erupted)</li>
</ul>

<p>Then my question is, with regards to the (seemingly unusually) recent date quoted in the above article:</p>

<p><strong>Why did the discovery of volcanic activity at sub-oceanic plate boundaries take so long?</strong></p>

CC BY-SA 3.0
2017-02-12T17:44:55.000Z
@ACuriousMind:  Sure.  Didn't think to look for "earth science" [blushes]
pr1268
CC BY-SA 3.0
2017-02-12T18:49:01.617Z
Because most of it is under quite a lot of water?
jamesqf
CC BY-SA 3.0
2017-02-13T01:37:59.413Z
Tectonic plate theory is only recently 'accepted' - 1950's or so... but 'why so recent' is a bit like asking why radio took 100 years after Maxwells equations to come about.

Maybe it just took time to physically confirm it...!
Coastal
CC BY-SA 3.0
2017-02-14T05:25:21.237Z
@Coastal: Actually, it was only about 40 years from the time Maxwell published his equations that Marconi made the first trans-Atlantic radio transmission.
jamesqf
<volcanology><earthquakes><history-of-science><ocean-ridge>
Why did it take so long to discover the volcanic nature of mid-oceanic ridges?
pr1268
# Why did it take so long to discover the volcanic nature of mid-oceanic ridges?

(Asked by: username_0 on 2017-02-12)

I just read [this article](https://www.nytimes.com/2016/01/12/science/midocean-ridges-volcano-underwater.html) and was astonished to see the following:

> Oceanographers stumbled on [the mid-oceanic ridges'] volcanic nature in 1973.

What I find surprising is how *recent* that is.

Considering that

* the [history of geology](http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=aa77) in general goes back at least 3 or 4 centuries
* the study of plate tectonics [goes back to 1912](http://www.ucmp.berkeley.edu/geology/techist.html) (even though it took a few more decades to gain wide acceptance)
* oceanic ridges were known at least [as early as 1872](https://en.wikipedia.org/wiki/Mid-Atlantic_Ridge)
* the correlation between [seismic activity and volcanoes](http://www.geology.sdsu.edu/how_volcanoes_work/Volcano_tectonic.html) has been known for some time (I don't know exactly how long, but *certainly* the Romans felt the ground shaking when Vesuvius' erupted)

Then my question is, with regards to the (seemingly unusually) recent date quoted in the above article:

**Why did the discovery of volcanic activity at sub-oceanic plate boundaries take so long?**

**Tags:** volcanology, earthquakes, history-of-science, ocean-ridge

> **Comments:**
> **username_0**: @ACuriousMind:  Sure.  Didn't think to look for "earth science" [blushes]  
> **username_1**: Because most of it is under quite a lot of water?  
> **username_2**: Tectonic plate theory is only recently 'accepted' - 1950's or so... but 'why so recent' is a bit like asking why radio took 100 years after Maxwells equations to come about.  Maybe it just took time to physically confirm it...!  
> **username_1**: @username_2: Actually, it was only about 40 years from the time Maxwell published his equations that Marconi made the first trans-Atlantic radio transmission.  

---

## 2 answers

### Answer by username_4 on 2017-02-13. Score: 9 | Accepted answer

If it weren't for WW2 and the search for German submarines, the discovery of mid-ocean ridges might have waited until satellite based gravimetric mapping in the 1980s. It was the use of fine magnetometers (if I remember correctly) used to detect submarines that discovered the banding of magnetic stripes on the Atlantic ocean floor, followed by it's mirror image after a certain mid-point in the ocean basin. When superposed with bathymetric maps, it was further discovered that these magnetic stripes had their counterpoint in the same topographic region on the other side of a high point.

The analysis of thousands of these ship transect records (released by the Navy following WW2) led to the creation of partial ocean floor maps revealed very long parallel strips of rocks containing magnetic reversals reflected in mirror symmetry on the opposite of a mid-ocean rise. Ocean drilling then confirmed that only a spreading volcanic ridge, spewing magma over tens of millions of years could create such features. Following that, precise seismological mapping also confirmed this developing "theory" of plate tectonics, that laid to rest Alfred Wegener's model.

These were heady times for the geologic community in the 60s and early 70s! All thanks to the Navy and WW2!

> **Comments:**
> **username_3**: This US Geological Survey page elaborates on that point (https://pubs.usgs.gov/gip/dynamic/developing.html): Beginning in the 1950s, scientists, using magnetic instruments (magnetometers) adapted from airborne devices developed during World War II to detect submarines, began recognizing odd magnetic variations across the ocean floor. This finding, though unexpected, was not entirely surprising because it was known that basalt -- the iron-rich, volcanic rock making up the ocean floor-- contains a strongly magnetic mineral (magnetite) and can locally distort compass readings.  
> **username_5**: They were actually looking for Russian submarines during the Cold War but otherwise this is a great answer.  

---

### Answer by username_3 on 2017-02-13. Score: 4

I think the [U.S. Geological Survey](https://pubs.usgs.gov/gip/dynamic/developing.html) has the gist of your answer -- prior to the mid-1900s, there wasn't enough seismological data to draw any conclusions:

> During the 20th century, improvements in seismic instrumentation and
> greater use of earthquake-recording instruments (seismographs)
> worldwide enabled scientists to learn that earthquakes tend to be
> concentrated in certain areas, most notably along the oceanic trenches
> and spreading ridges. By the late 1920s, seismologists were beginning
> to identify several prominent earthquake zones parallel to the
> trenches that typically were inclined 40-60° from the horizontal and
> extended several hundred kilometers into the Earth. These zones later
> became known as Wadati-Benioff zones, or simply Benioff zones, in
> honor of the seismologists who first recognized them, Kiyoo Wadati of
> Japan and Hugo Benioff of the United States. The study of global
> seismicity greatly advanced in the 1960s with the establishment of the
> Worldwide Standardized Seismograph Network (WWSSN) to monitor the
> compliance of the 1963 treaty banning above-ground testing of nuclear
> weapons. The much-improved data from the WWSSN instruments allowed
> seismologists to map precisely the zones of earthquake concentration
> worldwide.

This evidence led to [geophysicist Harry H. Hess hypothesizing seafloor spreading in 1960](https://www.britannica.com/science/seafloor-spreading-hypothesis). Researchers from Scripps Institution of Oceanography and Woods Hole Oceanographic Institute, among others, would spend years gathering evidence from the world's seafloors to test that theory, using oceanographic vessels, equipment, and analytical techniques that were not available in previous decades.


---

