Glassing

Glassing is the act of using high-energy weapons to bombard a planetary surface, which is melted in the immense heat, turning the silicate minerals on the upper layer of the crust into a glass-like mineraloid known as lechatelierite. While historically applied to intense nuclear bombardment, glassing is now more commonly associated with the Covenant practice of using starship-borne plasma weapons to bombard a planetary surface.

Process
Glassing is an operation carried out by a fleet of warships, bombarding a planet's surface with their weapons until the surface melts and flows in great lakes of lava. In the early stages, warships might carve symbols of religious significance into the crust, hundreds of meters deep and hundreds of kilometers across. In later stages, formations of warships fly in weaving patterns over the surface, or perform deep cuts in strategic locations.

Depending on the number of ships committed to the glassing, fully rendering an Earth-like planet uninhabitable can take months, even years. This represents a substantial commitment of energy, time, and resources, especially with fleets operating far from the heartlands of the Covenant Sphere. As long as a fleet is committed to a planetary glassing, it cannot move on to other targets, and has to contend with counterattacks. This was common throughout the Human-Covenant War, though more so in the early years, with the five-year Harvest Campaign being a notable example. In some cases where multiple human colonies were discovered in a short span of time, the Covenant would carry out rapid intersystem attacks to eliminate the UNSC forces present in the sector, and only then proceed to methodically glass those worlds completely.

Even in such cases, deep oceans were rarely glassed in their entirety as this would take prohibitively long amounts of time. Even if the entirety of the planet's surface is not subjected to bombardment, secondary effects of glassing (radiation, ash and dust in the atmosphere, wildfires, climate shifts) will typically render a planet hostile to human life.

Method of the Bleeding Wound
Simulations carried out by the UNSC in the early years of the war cast doubt on the idea that the Covenant could glass a planet's surface. Predictive models showed that glassing cities alone would be a colossal undertaking, and the energy requirement for evaporating oceans was orders of magnitude above what the Covenant could muster. Harvest was expected to be the only planet to be given this treatment, and the Covenant stopped well short of reducing its entire surface to glass.

But experience showed that the Covenant were more than willing to let volcanos and tectonics do their work for them. Covenant excavation beams can drill through miles of rock to reach pockets of magma, triggering apocalyptic lava flows. These vents usually require three to four warships working in coordination to dig so deep, as dozens more warships cut through hills and carve canals to carry the lava far away. The result are lava flows that cover millions of square kilometers, leaving islands of mountains and ridges.

The Method of the Bleeding Wound is not a simple process, even for the Covenant. Once the vent is opened and the lava begins to flow, it is nearly impossible to dig further. The vent must flow for months or even years, but if it closes up, it is almost impossible for the Covenant to re-open. For this reason, the Covenant only carry out the Method of the Bleeding Wound behind front lines. The excavating warships make easy targets, and any disruption to their work can force them to restart the whole project.

The UNSC took advantage of this by burying nuclear mines near likely dig sites. As Covenant warships need to partially drop their shields and fly slow to engage their excavation beams, a thirty-megaton warhead can mission-kill or outright destroy even an assault carrier.

Cultural Significance
The Covenant do not glass planets for practical or strategic reasons, as the process is about as far from practical as one can get. Not only is devastating inhabitable planets wasteful and inefficient, but there are faster ways to go about it. Once they have established orbital superiority, the Covenant could simply point a hypervelocity impactor at the planet to render it uninhabitable in a much shorter amount of time than it takes to commit to planetary glassing. However, glassing has a special religious importance to the Covenant, representing the most ultimate form of purification, a burning away of sin and corruption. Indeed, when applied on a large scale, glassing is more of a religious ritual than a military one. Its main strategic and political role is in its demoralizing effect and setting an example. It is not uncommon for energy projectors to be used in such cases, to carve religious symbols into the planet's surface on a vast scale, visible from orbit. Such rituals must always be overseen by a senior San'Shyuum official, usually a Prophet.

Glassing is rarely employed in intra-Covenant conflicts and is heavily restricted under the rules of Shal'annu, though it is sometimes used to set an example against rebellions or splinter groups deemed heretical or apostate. Even then, the full glassing of Covenant worlds is rare due to the strategic value of those worlds; more often, cities or bases are targeted with tactical glassing.

Use in the Human-Covenant War
As the war progressed, many Covenant fleets settled for glassing the major population centers before moving on when it came to most human colonies. Full planetary glassing was reserved for worlds whose destruction was deemed by religious officials to warrant special "purification". This was frowned upon by some Sangheili fleetmasters, who saw such acts as wasteful.

The plans to finish the glassing campaign were still on the board. Records indicated that the Prophet of Truth was amassing resources, both on High Charity and at the borders of Human territory, to completely glass every former Human colony. If the UNSC was ever broken, the pieces were in place to completely remove any trace of Humanity from the archeological record.

Since the end of the war, re-terraforming of glassed worlds has become relevant. Fully glassed planets may take well over a century to reclaim, while some colonies that only suffered localized glassing may be recoverable within years.