Basalt Column, Jurassic Period (190 million years ago), basalt rock, Beneski Museum of Natural History. Photo by the author.
Introduction
This column of basalt is a representation of volcanic activity from almost two hundred million years ago. While volcanoes are not typically considered a regular weather phenomenon, the processes that surround and result from volcanic activity heavily impact weather on long, geologic timescales. While weather is an experience of observable above-surface Earth processes over a relatively short period of time, basalt represents the deep Earth processes that guide, shift, and create weather across the globe. Contrary to instinct, volcanic activity represents creation just as much as it represents destruction. The same events that result in the formation of this basaltic rock also influence the topographic makeup of any particular region, as well as its constantly shifting location on the globe. These two factors are both responsible for the creation of observable weather and essential to understanding how weather exists and shifts through time.
Basalt Column, Jurassic Period (190 million years ago), basalt rock, Beneski Museum of Natural History. Photo by the author.
Description
The column of basalt most obviously appears as a rough, heavy block of dark gray rock. Upon closer examination, one can observe how it is slightly speckled with reddish-orange on the outermost edges with six distinctive sides that form a hexagonal shape. Basaltic lava structures typically divide into tall, tower-like “columns” that appear split into vertical, polygonal “joints.”1 Although they form naturally, they have a configuration like one of man-made geometric shapes—hexagons, to be specific. Historically, the origins of the strange, hexagonal shapes these natural landforms take were attributed to different aspects of religion and culture. These ideas are reflected in the names the most notable basaltic landforms have, such as the Devils Postpile in California, Giant’s Causeway in northern Ireland, and, closest in location to Massachusetts basalt, Devils Tower in Wyoming. Modern geologists have come to understand that the hexagonal patterns formed during the “cooling and solidification” of lava.2 These patterns are often hypothesized to reflect the path of lava flow that minimizes the “fracture surface energy” and “strain energy” of a system.3
Both the column of basalt and Devils Tower are generally made of the same material, but there are some key differences in chemical composition that form during the cooling process of igneous rocks that differentiate Devils Tower from this particular column of basalt. Devils Tower is composed of phonolite porphyry rock, which typically cools slowly underground to form large crystals. These rocks appear red or gray when “fresh” and green or brown after experiencing “weathering,” or elements that factor into erosion (such as wind and rain).4 Erosion plays a large role in geologic landforms and how they exist through time, and this particular rock changes color after experiencing wind and rain. Basaltic rock, on the other hand, is formed from rapid-cooling lava, turning either black or gray. The column of basalt in Beneski, however, seems to have reddish-orange parts embedded into the rock.5 Because of its close similarity to the geologic composition of Devils Tower (and phonolite porphyry), the appearance of this red color begs the question of whether or not different parts of this particular column cooled at different rates underground. While most of it cooled at the rate basaltic lava typically cools, which is fast, some of it could have cooled closer the the surface at a slightly slower rate, which would result in phonolite porphyry crystals that constitute the reddish colors in the column.
Research
Medium
Basalt is melted upper mantle peridotite that rose and cooled down once exposed to the cooler atmospheric temperatures above the lithosphere.6 Basalt typically cools to form lithospheric ocean crust, but it can also form landmarks like Devils Tower when the cooling process occurs at different rates. Oceanic crust forms at mid-ocean ridges because, when tectonic plates pull apart, the hot mantle rocks beneath the surface are given a chance to rise and cool. This is essentially what constitutes basaltic volcanoes in a geologic sense. Oceanic crust, or basalt, is denser than continental crust, causing it to fall lower in elevation than continental crust. The basalt at mid-ocean ridges is relatively buoyant, so it typically rises to form islands or accumulates into volcanic arcs. The barren land formed from these new volcanic land masses are often starting points for where new life can begin to form. A critical component of basalt rock is its extreme chemical weatherability, which allows it to break down quickly when exposed to elements like rain.
Context
This slab of basalt formed, or cooled, approximately 190 million years ago, during the Jurassic Period. During this time, the continental lithosphere that Massachusetts lay on was likely a subduction zone where oceanic and continental plates collide. A common occurrence at these plate boundaries, when active, is volcanic activity because of the difference in density between the two plates. Oceanic crust subducts beneath the less dense, thicker continental crust and melts in the upper mantle, causing hot rocks to rise and form hot volcanic basalt.
The basalt has experienced many different weather events over the millions of years it has existed. While it is stored indoors today, it was previously exposed to elements of rain and wind that broke down the rock and changed its appearance drastically from when it first formed. While the six hexagonal sides are visually clear, they are less pronounced after experiencing weather over millions of years than they were when the rock first formed.
The climate today looks different geographically, biologically, and atmospherically than it did during the Jurassic period. If it were still outdoors, the latitude Massachusetts exists at today (42°) would expose the rock to drastically different weather than it was exposed to at its creation 190 million years ago. Then, its latitude was slightly lower (about 20°), so the climate could have been more similar to the Southeast of the United States today, but not drastically so.7 Devils Tower underwent similar degrees of latitude change (30° to 50°) and is said to have the same shape as it did when the magma first cooled during the Triassic to Late Jurassic periods.8 Because Devils Tower is a close comparison for this column of basalt, it is likely that, despite how its geographic location changed as continents formed and shifted, the basalt has maintained this hexagonal shape, width, and stability for around two hundred million years.
Provenance
The column of basalt can be found in the Beneski Museum on the second floor, in the Connecticut River Valley Geology Exhibition. The Beneski Museum often partners with the geology department to collect “museum grade” specimens and samples for display. In 2005, the geology department at the time commingled with Benski to collect and incorporate many of the samples on the second floor into the Geology of the Connecticut River Valley exhibition. The thought process in 2005 (and currently) was to use the second floor as a tool for teaching the geological background of (Amhert’s) region throughout time. Unfortunately, the column of basalt was spruced from the geology department, making it officially “uncatalogued” in Beneski. This means that this particular object lacks “formal provenance information”; however it is likely that this object was one of the many that were sourced in 2005 for the exhibit.9
Weather
Basalt represents volcanic activity. At a base level, volcanic activity typically occurs at mid-ocean ridges or subduction zones, both of which provoke the creation of new land in the form of volcanic arcs and islands made of basalt rock. In this way, volcanoes simultaneously destroy life (with lava) while creating a base for new life to form on barren (basaltic) land. After a “volcanic disturbance,” these rock platforms “develop vegetation” that learns to thrive on the newly formed landmass.10 Volcanoes in the Jurassic period played a crucial role in developing a changing climate that influenced mass extinctions, ice ages, and distributions of environments around the globe.
An essential aspect to understanding how basalt experiences weather is understanding how it exists through time as a vessel for creation. The impact volcanoes climatically trickle down to heavily influence weather. During the Jurassic Period, dinosaurs thrived and birds evolved as the Earth’s climate adapted and warmed from its previous (cooler) glacial state. As supercontinents broke apart, basalt’s extreme weatherability played a vital role in the planet’s changing climate and regulation. The formation and eruption of volcanoes releases large amounts of carbon dioxide into the atmosphere that strengthens the greenhouse effect. Warmer air can hold more water, so with a warmer atmosphere comes increased precipitation. Precipitation directly influences the most impactful type of weathering basalt encounters: chemical weathering. Basalt is highly sensitive to water because it starts the chemical weathering process that essentially removes carbon dioxide from the atmosphere. In volcanic eruptions there exists a balance that simultaneously releases carbon dioxide (in eruption) and eliminates it (in basalt’s chemical weathering). Essentially, it creates an environment where rain is more abundant, while, at the same time, experiencing quick decomposition as a result of rain-induced chemical weathering.11 This rain and chemical weathering can change the color of certain basaltic landforms, like Devils Tower, from gray to a shocking green or brown. Additionally, the increased carbon dioxide directly impacts how warm an area is, therefore controlling the extremity of heat, or hot weather, that the basalt exists in. Altogether, the formation of basalt influences the weather it experiences after being produced – it creates a climate, but experiences a weather. Although basalt is most easily recognized as a representation of climate change, it also represents the simultaneous creation and experience of weather.
Footnotes
- Atila Aydin and James M. DeGraff, “Evolution of Polygonal Fracture Patterns in Lava Flows,” Science 239, no. 4839 (1988): 471–76. ↩︎
- DeGraff, “Evolution,” 472. ↩︎
- DeGraff, “Evolution,” 475. ↩︎
- Charles Sherwod Robinson, “Geology of Devils Tower, Wyoming,” U.S. Geological Survey, no. 1021 (1956): 289–302, https://pubs.usgs.gov/bul/1021i/report.pdf. ↩︎
- Softus Vista Inc., “Basalt vs. Phonolite,” 2010, https://rocks.comparenature.com/en/basalt-vs-phonolite/comparison-7-130-0. ↩︎
- Roger C. Searle, “Plate Tectonics,” in Encyclopedia of Islands, ed. Rosemary G. Gillespie and David A Clague (University California Press, 2009), 752–55. ↩︎
- C.R. Scotese and Ian Webster, “Global Plate Tectonic Model,” Ancient Earth & Dinosaur Database https://dinosaurpictures.org/ancient-earth#750. ↩︎
- Robinson, “Geology of Devils Tower,” 289. ↩︎
- Conversation with Hayley Singleton, Beneski Museum of Natural History, April 2025. ↩︎
- Bruce D. Clarkson, “A Review of Vegetation Development Following Recent (<450 years) Volcanic Disturbance in North Island, New Zealand,” New Zealand Journal of Ecology 14 (1990): 59–71. ↩︎
- Andrew Williams and Darrell Weyman, “Up-dating Geomorphology: Chemical Weathering Processes,” Teaching Geography 6, no. 2 (1980): 67–71. ↩︎