Assibilation

Assibilation is a phonological process where a non-sibilant sound (like "t" or "d") becomes a sibilant sound (like "s" or "sh") in certain phonetic environments. 
The words "explode" to "explosion" and "navigate" to "navigation" are good examples of this process:

Explode -> Explôsion:

In "explode," the "d" is a non-sibilant sound.
When we add the suffix "-ion" to form "explôsion," the environment around the "d" changes.
The "d" is followed by the vowel sound "i" in "-ion," which is a high front vowel. 
This proximity to a high front vowel triggers the assibilation process.
As a result, the "d" sound is transformed into an "zh" sound, and "explode" becomes "explôsion." 
This change makes the pronunciation smoother in the transition from the consonant to the vowel.

Navegaite -> Navegâcion:

In "navegaite," the "t" is a non-sibilant sound.
Adding the suffix "-ion" to form "navegâcion" changes the phonetic context of the "t."
Similar to the previous example, the "t" is now followed by a high front vowel sound ("i" in "-ion").
This causes the "t" to undergo assibilation, changing to a "sh" (ʃ) sound. Therefore, "navegaite" becomes "navegâcion."
In both cases, assibilation occurs because the addition of the "-ion" suffix places a high front vowel after a non-sibilant consonant, 
causing the consonant to shift to a sibilant sound for easier and more fluid pronunciation. 
This is a common feature in many languages, including Inglish, 
and is particularly noticeable in words of Latin origin where the "-ion" suffix is prevalent.

Additional examples:

to erode + ion -> eroôsion
ta corrode + ion -> corrôsion
to envâde + ion -> envâsion
ta persuâde + ion -> persuâsion
ta colîde + ion -> colis̃on
ta divîde + ion -> divis̃on
ta decîde + ion -> decis̃on
ta provîde + ion -> provis̃on

ta criâte + ion -> criâcion
ta vâqete + ion -> vâcâcion
ta graᶁuete + ion -> graᶁuâcion
to assoçiete + ion -> assoçiâcion
to apríçiete + ion -> apríçiâcion
to iniçiete + ion -> iniçiâcion
ta negoçiete + ion -> negoçiâcion
ta diffrençiete + ion -> diffrençiâcion
ta repeudiete + ion -> repeudiâcion
ta mitigaite + ion -> mitigâcion