Hotspots or volcanic activities are sources of volcanic eruptions from the Earth’s interior or deep magma which do not result from its plate tectonics movements. This is because they remain fixed as it moves over them leading to a line of volcanic islands or mountains through many geological eras. 

Features:

1. Origin: The origin of the hotspots is thought to be deep inside the earth’s mantle, possibly close to the core-mantle boundary, where heat and pressure would lead to the melting of rocks in the mantle and their transformation into lava.
2. Stationarity: Unlike the shifting tectonic plates, mantle plumes are relatively fixed in their positions. As the tectonic plates move over these stationary hotspots, a chain of volcanoes can form.
3. Formation: As a tectonic plate moves over a hotspot, magma rises through the crust, creating volcanoes. Over time, this process can form a linear series of volcanic islands or seamounts.
4. Unique Composition: Magma from hotspots often has distinct geochemical signatures, differing from magma generated at mid-ocean ridges or subduction zones. These signatures can include higher levels of certain isotopes and elements.
5. Heat Flow: Hotspots are associated with higher than average heat flow due to the rising hot mantle material. This thermal anomaly can be detected through heat flow measurements.

Examples:

Hawaiian Hotspot, Central Pacific Ocean

Yellowstone Hotspot, Western United States

Iceland Hotspot, North Atlantic Ocean