To understand this scene it really helps to understand the process that forms calderas and that also formed this volcano.
This Wiki quote is integral to understanding this volcano on Pluto so read it and understand it.
A caldera is a large cauldron-like depression that forms following the evacuation of a magma chamber/reservoir.
When large volumes of magma are erupted over a short time period, structural support for the crust above the magma chamber is lost.
The ground surface then collapses downward into the partially emptied magma chamber, leaving a massive depression at the surface (from one to dozens of kilometers in diameter).
Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact.
A collapse is triggered by the emptying of the magma chamber beneath the volcano, sometimes as the result of a large explosive volcanic eruption (see Tambora in 1815), but also during effusive eruptions on the flanks of a volcano (see Piton de la Fournaise in 2007) or in a connected fissure system (see Bárðarbunga in 2014–2015).
Understanding the formation of the caldera as a collapsed sink hole emptying the chamber is important.
But even more important, within that Wiki quote, is the effusive eruptions on the flanks of the volcano.
You are about to see something that has taken me 2 years to understand but before that, check out this caldera forming flour animation analogue experiment.
There is a feature on Pluto that has puzzled me over and over.
I've stared at, pondered it, tried to label it and it has continually escaped my ability to comprehend it, until now.
This feature is directly connected to the flank of Pluto's Kilauea volcano
Quote from Nervous System Blog
Lava is the molten rock expelled by a volcano during an eruption. Lava flows can have very different properties based on their chemical composition, temperature, eruption rate, crystal content, and bubble content.
The current lava flow in HawNervous System Blogaii is an effusive flow of basalt with low viscosity and high temperature. It flows quickly and smoothly, leaving glassy rippled rock in its wake. Geologists call this type of flow pahoehoe, a Hawaiian name that equates the lava forms to swirling water (“hoe” = to paddle). This is an apt name as the lava rock is festooned with incredible patterns of contorted wrinkles, ripples, and folds. What causes these forms?
Lava Flows and Folds
When lava flows, the outside layer quickly cools forming an exterior crust. In fact, many of the lava patterns we found were quite thin and hollow inside where the lava had subsequently evacuated after the structures were formed.
This cooled layer is significantly more viscous than the lava below acting like a viscous sheet. Folds begin to form when the flow compresses due to the slowing of the flow front.
This compression could be caused by hitting an obstruction or entering a narrow channel. These folds form in the span of seconds to minutes.