Constructive plate boundaries, or divergent boundaries, occur where plates move apart, allowing magma to rise from the mantle to form new crust. When this occurs on the ocean floor, it is referred to as underwater or submarine volcanism, which is responsible for the creation of mid-ocean ridges and seafloor spreading.

Mid-oceanic ridges are formed by underwater volcanic activity at divergent plate boundaries. As plates pull apart, magma rises from the mantle to fill the gap, cooling to form new oceanic crust and creating a continuous mountain range along the seafloor.

Basic lava, also referred to as mafic lava, is rich in iron and magnesium and low in silica. Because of its low silica content, it has low viscosity, allowing it to flow easily and cover large distances before cooling and solidifying. This contrasts with acid lava, which is high in silica and much more viscous.

Composite volcanoes, also known as stratovolcanoes, are characterized by highly viscous, silica-rich magma. This viscosity prevents gases from escaping easily, leading to a significant buildup of pressure within the magma chamber. When an eruption occurs, this pressure is released explosively, resulting in loud, violent events that often eject ash, pyroclastic flows, and volcanic bombs. These eruptions are significantly more destructive than the effusive eruptions typically associated with shield volcanoes.

At a destructive or convergent plate boundary, the denser oceanic plate is forced beneath the lighter continental plate in a process called subduction. As the oceanic plate descends into the mantle, it undergoes partial melting due to high temperatures and pressure, generating magma that rises to form volcanic arcs on the overriding continental crust.

Composite volcanoes, also known as stratovolcanoes, are built from alternating layers of lava flows, volcanic ash, and cinders. Because they are constructed from these varied materials, they are frequently referred to as ash and cinder cone volcanoes. These structures are typically steep-sided and capable of producing highly explosive eruptions due to the viscous nature of their magma.

Basic lava, also known as basaltic lava, has low viscosity and gas content, typically resulting in effusive eruptions. However, when explosive activity occurs, volcanic ash—composed of pulverized rock, minerals, and volcanic glass—is the most common particulate matter ejected into the atmosphere. While gases like CO2 are released, ash is the primary solid material thrown out during such volcanic events.

Composite volcanoes, or stratovolcanoes, are characterized by highly viscous acid lava. This high viscosity traps volcanic gases, leading to a massive buildup of pressure that is eventually released in violent, explosive eruptions rather than gentle lava flows.

Mount Kilimanjaro is a dormant volcano in Tanzania and is the highest mountain in Africa. It is a classic example of a stratovolcano formed by the accumulation of lava, ash, and volcanic debris over time. In contrast, the Rockies, Urals, and Alps are primarily fold mountains created by tectonic plate collisions, making Mount Kilimanjaro the correct choice for a volcanic landform.

Mantle plumes are hypothesized to be upwellings of abnormally hot rock within the Earth's mantle. These plumes rise from deep within the mantle, often near the core-mantle boundary, and are responsible for creating volcanic hotspots that are independent of tectonic plate boundaries, such as the Hawaiian Islands.