The United States contains 161 volcanoes which are considered to be active or potentially active per
the U.S. Geological Survey, largely meaning that they have erupted or are suspected to have erupted
at some point since the end of the last ice age and/or have an active magma chamber. Additionally,
there might be a 162nd active volcano somewhere in far western Alaska as a
quarter of an inch of ash fell on Nome from an unidentified volcano in November of 1907.
Yet, if we turn on a map of all of these volcanoes, the vast majority are easy to explain,
as they originated due to the collision of two tectonic plates. Yet, there are also unusually
placed volcanoes which exist far away from plate boundaries or regions where crustal rifting is
occurring. For example, the Hawaiian Island chain, which exists more than 2000 miles from the nearest
major tectonic plate boundary. There, the 6 active volcanoes which exist are all caused by
what is termed a "mantle hotspot". Per a direct quote from a U.S. Geological Survey webpage,
"...hotspots form over exceptionally hot regions in the mantle, which is the hot,
flowing layer of the Earth beneath the crust. Mantle rock in those extra-hot regions is more
buoyant than the surrounding rocks, so it rises through the mantle and crust to erupt at the
surface." Since hotspots as a whole largely do not move but the crust above them does,
mantle hotspots often form a chain of observable volcanic features where across the landscape in
one direction is progressively older, with features only being active while the mantle
plume or hotspot is in close proximity to them before becoming permanently extinct. For example,
as we go westwards the Hawaiian islands get older and older in age, going from active volcanoes,
to extinct volcanoes, until you reach only a chain of seamounts. The so-called Hawaiian
Emperor Seamount Chain which exists due to this hotspot stretches nearly 4,000 miles,
almost touching Russia's Kamchatka peninsula and the far western end of the Aleutians,
with the oldest feature dated to 81 million years in age. However, although not found at every
mantle hotspot, another way to identify a portion of these features is to find a massive province of
volcanic rocks often several thousand feet thick covering several thousand square miles. These
features are known as flood basalts and occur when the figurative head of a mushroom shaped mantle
plume first reaches the crust. For example, the still active Yellowstone Hotspot in Wyoming began
its life through producing the Columbia River Flood Basalts, covering 80,000 square miles of
land in Oregon, Washington, and Idaho in up to 10,000 feet thick of primarily basaltic lava.
With this being said, there are two more mantle hotspots which can be found in the
United States. One exists beneath the fareastern end of American Samoa while another although
unconfirmed might exist underneath Flagstaff, producing occasional eruptions at the San
Francisco Volcanic Field. Although evidence is somewhat weak for this, the volcanic field
gets progressively older to the west, marking the same direction the North American Plate is moving.
In addition to the two hotspots found off the western coasts of the United States and Canada,
there is also a hotspot in Canada proper, having powered infrequent volcanism for several million
years with its most recent eruption being the latest Nazko cone eruption in 5200 BCE.
However, the planet has many more mantle hotspots. In the rest of this video,
I will quickly showcase each of the remaining 41 hotspots, which under my criteria are only counted
if they have produced in some form a volcanic eruption during the last 1 million years. And,
I want to note that the existence of some of these hotspots is more questionable than others,
with highly uncertain hotspots that might not even exist being the Flagstaff, Guadalupe,
Karisimbi, Peter I, and Rungwe Hotspots. In the Atlantic, Jan Mayen, Iceland, Madeira,
the Canary Islands, Cape Verde, Trindade, Ascension, Gough, Tristan de Cunha, and
Bouvet islands exists due to separate hotspots. In Africa, the Hoggar, Tibesti, and Afar hotspots
are each responsible for geologically recent volcanism. In the Indian Ocean the Marion,
Crozet, Kerguelen, Heard, Comores, and Reunion islands exist due to hotspots. Germany has the
Eifel Hotspot, Russia has the Baikal Hotspot, and China has the Hainan Hotspot. Balleny and Erebus
hotspots exist in Antarctica, while the Socorro and Baja Hotspots exist off the western coast of
Mexico. And finally, in the vast Pacific Ocean we have the Caroline, Easter, Foundation, Galapagos,
Juan Fernandez, Louisville, Macdonald, Marquesas, Pitcairn, San Felix, and Society Hotspots.
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