Final answer:
Large, cone-shaped volcanoes on the seafloor that have not breached sea level are known as submarine volcanoes. They are related to the geological formations that occur at tectonic plate boundaries and hot spots below the Earth's crust, much like the volcanic activity that created the Hawaiian Islands.
Step-by-step explanation:
Large volcanoes on the seafloor that are cone-shaped on top but have not reached sea level are known as submarine volcanoes. These geological formations often resemble the larger shield volcanoes found on land; however, they remain submerged and may go unnoticed. One familiar example of volcanic activity above sea level is the Hawaiian Islands, which were formed over a hot spot in the Earth's crust. Submarine volcanoes play a crucial role in the formation of the seabed, especially at tectonic boundaries such as mid-ocean ridges and subduction zones, where the Earth's crust is continuously recycled.
Another kind of submarine volcanic formation can be found on other planets, such as Venus, where pancake-shaped volcanoes have been discovered. These volcanoes are formed by highly viscous lava that spreads out evenly in all directions. Like Earth's submarine volcanoes, these extraterrestrial formations provide insight into the geological processes at work beneath the planet's surface.