Around the time of the last ice age, Tower Hill was created through a series of volcanic events that resulted in the formation of a Maartype volcano.

Approximately 32,000 years ago a basaltic lava column rising through the crust comes in contact with the ground water.

Activity stops when pressure of rising lava and steam decrease. A thick 200-300 metre layer of basalt accumulates in the crater. Later activity, less explosive than the first, produces the scoria cones in the centre.

Steam is generated and the lava breaks up and forces its way through to the surface. Large blocks of displaced crust are surrounded by rising ash. Many explosive eruptions follow ejecting ash and scoria, both as a vertically rising column and as dense clouds which travel up the crater's sides. Ash and scoria, both from these radially moving clouds above, build up the layered tuff ring.

Tower Hill today.

Typically a wide funnel-shaped crater volcano, Maar volcanoes form through the fracturing and slumping of the ground from sub-surface volcanic activity.  Further explosions deepen the crater, which is ringed by a very low cone of deposited material sloping away from the crater.

A Maar volcano forms when hot, rising magma comes into contact with sediments that are saturated by cold groundwater. High pressure steam is created and the magma is fragmented resulting in explosions which shatter the overlying rock. The ground collapses forming a vent allowing steam to escape in a turbulent fashion.

The vent deepens as subsequent explosions occur. The surrounding ground is gouged-out and the walls of the crater collapse inwards. The displaced material is  pulverized forming ash, which with the magma and other particles of varying sizes is flung violently into the air with the escaping gas and steam.

Debris rains down over the surrounding countryside in the direction of the prevailing wind. Larger materials fall first, closer to the crater, finer material is carried by the wind and deposited further afield. The debris forms regular layers of ash (tuff) around the crater rim. At Tower Hill, this tuff-ring varies in height from 5m in the southwest to 110m in the northeast and debris from the eruption is found up to 20km away.

The base of the resulting crater is always lower than the original ground surface. At Tower Hill, the crater floor is 40m below the original surface and 13m above sea level. It is relatively flat, but deeper in the south western corner where water stands even in times of drought.

As the amount of groundwater in the sediment lessens, the number and size of eruptions lessen. Lava fountaining commences, creating small scoria cones in the crater. These eruptions are comparatively small, but colourful and noisy.

Under pressure, a jet of red, hot, lava, is sprayed from vents by blasts of escaping gas, often reaching 100m in the air. Glowing lumps of frothy lava shower the immediate area. Cooled on contact with air, the scoria accumulates as rubble around the vent, building up a cone shape known as a cinder cone. Such scoria cones form the 'islands' of Tower Hill.
 
Today Tower Hill is a more peaceful place. It is rated as a geological feature of State and National significance and was added to the Victorian Heritage Register in 2006.