The Irmo plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
Sunny
Mostly sunny
Mostly sunny
Sunny
Sunny
Mostly sunny
Mostly sunny
75° on Nov. 11, 2024, the hottest reading for this week of the year since 1924. Next is 72° in 1931.
Irmo’s center stands about 360 ft above sea level. Within three miles the land runs from 200 ft to 460 ft, a difference of 260 ft: rolling country. The highest named summit within 15 miles is Little Mountain, about 830 ft, 15 miles west-northwest.
Under the town center the state geologic map shows Asbill Pond Formation (metasiltstone, metasandstone), from the Middle Cambrian, 497 to 521 million years old.
The section below crosses 8 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 49×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Metavolcanic. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 7 mi of the line.
Metasiltstone, metasandstone. Age: Middle Cambrian, 497 to 521 million years old. About 5 mi of the line.
Mylonite. Age: Carboniferous to Permian, 252 to 359 million years old. About 3 mi of the line.
Slate. Age: Middle Cambrian to Ordovician, 445 to 521 million years old. About 3 mi of the line.
Granite. Age: Carboniferous to Permian, 252 to 359 million years old. About 2 mi of the line.
Sand, gravel. Age: Cretaceous, 66 to 145 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 2 smaller units along the line are not listed.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in Irmo reaches the Atlantic Ocean by way of Rawls Creek, the Saluda, the Congaree, the Santee and the South Santee: about 190 river miles.
Lake on the way: Lib Pines Lake.
70 miles of the trip are on the Santee.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Irmo; river miles along the main stem, rounded.
Irmo has a oceanic climate. Summer afternoons average 78° in July; winter nights fall to about 28° in January. A normal year brings about 7 inches of snow; with the rain, that comes to about 74 inches of water.
On November 14 Irmo normally reaches 55° and falls to 38°. The record high is 72°, in 1931; the record low 16°, in 2019. The most rain on this date, 2.40 in, fell in 1961.
Normals 1991–2020 and records since 1924 from the Caesars Head Area threaded record (Columbia Metropolitan Airport, 11 miles south-southeast, 140 ft lower). NOAA, through RCC-ACIS.
