use of present participle as modifier

[vaishalijain7]

Geologists once thought that the molten rock known as lava was an underground remnant of Earth's earliest days, sporadically erupting through volcanoes, but they now know that it is continuously created by the heat of the radioactivity deep inside the planet.
(A) was an underground remnant of Earth's earliest days, sporadically erupting
(B) had been an underground remnant of Earth's earliest days and sporadically erupted
(C) was an underground remnant of Earth's earliest days, which sporadically erupted
(D) would be an underground remnant of Earth's earliest days that sporadically erupted
(E) was an underground remnant of Earth's earliest days, having sporadically erupted

OA is [spoiler]'A'[/spoiler]. Can anybody please tell me why are we using present participle "erupting" to modify "underground remnant". As I know present participle is used after comma to modify the whole phrase preceded by comma.

[SanjeevK]

"erupting" is modifying "lava" and not "underground remnant".
lava is still erupting.
Hope this makes sense

[goelmohit2002]

But differnent questions in OG give different explanations what "ing" modifier modifies...sometimes they say subject, sometime action, sometime entire previous clause....

Can someone please help me understand what is indeed the case.