Trench has a specific meaning in plate tectonics. It doesn't just refer to any valley; it specifically refers to the features formed at subduction zones by the flexure of the downgoing oceanic plate. A classic example is the Marianas Trench which is the location of the deepest point in the ocean
Fast spreading ridges do indeed have valleys at their centre ...
Yes, there are many. According to the seafloor topographic data of ETOPO (1 arc second resolution), and the Exclusive Economic Zones (EEZ) database of marineregions.org. There are at least 157 seafloor features higher than -100 m (closer than 100 m to the sea surface). With that data, I made the following figure that shows:
ETOPO topographic data
All EEZ ...
The oceanic plates are themselves formed from the divergent boundary, so probably not. Even if a new rifting occurred exactly at the boundary, the result would eventually be that the ocean floor surrounds the divergent boundary.
A very simplified model of an ocean would have a divergent boundary in the middle. This oceanic spreading center might have ...
Checking the Wikipedia page on underwater volcanoes and listing them by height, I think the best candidate is Vema Seamount. Vema Seamount is in international waters and its shallowest point is at 11 meters from the surface. It is so shallow that it represents a navigation hazard.
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 ...
The fact that these three features are parallel may be somewhat coincidental, although we can suspect that tectonic forces have influenced their morphology. The crust under the Arctic Sea is one of the least understood regimes in the world.
This is changing - whichever country can prove that their nation's continental shelf extends along one or more of ...
Hot spots and ridges are two different things.
Hot spots stay in one place while the earth crust above them drifts and thus create a line of dormant volcanoes, they are a point features so to say.
Ridges are places where the mantle convection wells up and spreads in two directions, gently pulling the earth crust with them and creating new crust where the ...
Let's clear up the terminology first:
A trench, as @bon has described in their answer, is formed where tectonic plates move towards each other and one of the plates is subducted under the other. @bon has also provided an illuminating illustration. The German term for an oceanic trench is Tiefseerinne (literally "deep sea groove").
The majority of Earth's volcanoes occur in plate boundaries. These can be at spreading ridges (green dots on the map) where they are mostly underwater, but sometimes are above the water (such as in Iceland). They can also be on convergent margins, for example the Pacific ring of fire.
A less common type of volcano is the intraplate volcano, which are ...
Intraplate volcanism - as the name suggests it is volcanism within the plates rather than at plate boundaries.
These are also known as hotspots.
Ocean island basalt (OIB) - is the basaltic rocks associated with intraplate volcanism.
Relation between mid-ocean ridges and hotspots:
Hotspot–ridge interaction produces a wide range of phenomena ...
The elevation of oceanic crust is controlled by Pratt isostasy, whereby hotter crust is elevated because it is less dense. Oceanic crust is produced at mid-ocean ridges and cools as it moves away from the ridge. Mid-ocean ridges are hot and therefore they are elevated above the colder, more dense adjacent crust.
In continental rifts, the dominant process ...
I think the U.S. Geological Survey 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
Helium is formed through the radioactive decay of uranium 238, uranium 235 and Thorium 232. A helium atom is an alpha particle that has collected electrons. The only way that helium is produced on Earth is by such radioactive decay deep underground.
Generally, the helium travels along cracks until it reaches a subterranean cavern where it accumulates.
Are Helium 3 and 4 being produced by earth's core?
The paper you are referring to has major flaws in it. Claims that should not be in any respectable scientific journal such as:
...the demise of the georeactor is approaching. Within the present level of uncertainty, one cannot say precisely when georeactor demise will occur, whether in the ...
hot spots help/control how spreading centers form but they are not what keeps them going.
If you push on a thin amorphous material perpendicular to the surface they tend to crack/split at three cracks roughly ~120 degrees to each other. If you push at several points close enough to each other these cracks will tend to link up as long lines with 120 degree ...
Intra = within/on the inside, so intraplate volcanism would be volcanism happening far from plate boundaries, usually hotspots.
If you have trouble remembering intra- vs inter- remember international trade = trade from one nation to others, domestic trade would be intra-national trade even though no one uses that term.
Reading this question, I'm not sure if you realize what an isotherm is - in this case, imagine peeling rock from the surface of the earth until you reached a temperature of 1300 degrees Celsius. Now, in some areas, such as mid ocean ridges, you wouldn't have to peel back much rock at all, perhaps only a few dozen kilometers. Whereas in regions of old, ...
A Graben/Rift valley is more attuned to divergent plate environment where as a Trench is mostly used and accepted when convergent plate activities is under discussion, other wise the two portray the same geological features/meaning.
You May think of this situation as following:
Consider an ocean-ocean divergent boundary and one of the oceanic plates (OP) is subducting below the continental plate (CP). Following shows such a setting.
OP= Oceanic Plate.
MOR= Mid Oceanic Ridge.
CP= Continental Plate
\ \ = shows subduction