Route 1 — the Ring Road — stitches Iceland's 1,332-kilometre perimeter together, but the 180-kilometre stretch east from Reykjavik carries the nation's most concentrated corridor of geological drama. Skógafoss drops 60 metres over a former sea cliff that once marked Iceland's southern coastline before centuries of glacial meltwater pushed the shore five kilometres seaward. Seljalandsfoss, thirty kilometres west, offers the only major Icelandic waterfall where visitors can walk a full circuit behind the curtain of water — a basalt alcove carved by millennia of hydraulic erosion. Both falls draw from rivers fed by Eyjafjallajökull and Mýrdalsjökull, the ice caps that cover two of Iceland's most active volcanoes. The south coast's black sand beaches — Reynisfjara chief among them — are not sand in the silicate sense. The fine basalt gravel is pulverised volcanic rock, fragments of cooled lava ground down by Atlantic surf. Reynisdrangar, the three basalt sea stacks rising 66 metres offshore, are the remains of a coastal cliff formation that resisted wave erosion while the surrounding stone retreated. Icelandic folklore attributes the stacks to trolls caught by sunrise and turned to stone. Geologists date the columns to the last ice age, when subglacial eruptions produced the hexagonal basalt that now defines the southern coastline. Mýrdalsjökull, Iceland's fourth-largest glacier at 596 square kilometres, conceals Katla, a volcano with an eruption cycle averaging once per century. The glacier tongue Sólheimajökull descends from the ice cap's southern edge, advancing and retreating with seasonal melt patterns measured annually by the Icelandic Meteorological Office. The lagoon at its terminus, strewn with icebergs calved from the glacier face, did not exist before 1950. Warming trends accelerated the melt rate from 12 metres per year in the 1990s to 40 metres annually by 2020, creating the present-day lagoon and exposing crevasse fields that were previously buried. South coast tours from Reykjavik typically follow the same Route 1 corridor, stopping at the same five landmarks, but small-group departures cap capacity at 19 passengers — enough to preserve mobility at overlook points where tour buses deposit 50 travellers at once. The village of Vík í Mýrdal, the southernmost settlement on Iceland's mainland, anchors the eastern terminus. Its red-roofed church, built in 1932, sits 72 metres above sea level — the designated evacuation point should Katla erupt beneath Mýrdalsjökull and trigger a jökulhlaup, the Icelandic term for glacial outburst flood. Sensors embedded in the ice cap measure seismic tremors in real time, feeding data to a warning system that has been tested but never activated in the modern era.