{"id":1319,"date":"2026-05-12T21:47:34","date_gmt":"2026-05-12T21:47:34","guid":{"rendered":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/formation-of-fractures\/"},"modified":"2026-05-13T03:24:47","modified_gmt":"2026-05-13T03:24:47","slug":"formation-of-fractures","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/formation-of-fractures\/","title":{"raw":"16.4 Formation of Fractures","rendered":"16.4 Formation of Fractures"},"content":{"raw":"<div id=\"formation-of-fractures\" class=\"level1\">\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nThere are generally three modes of fracture loading, which involve different fracture surface displacements (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>). The three modes are listed here.\r\n\r\n<\/div>\r\n<ul>\r\n \t<li>Mode 1: opening or tensile mode\u2014the fracture faces are pulled apart (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>a).<\/li>\r\n \t<li>Mode 2: sliding or in\u2011plane shear\u2014the fracture surfaces slide over each other (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>b).<\/li>\r\n \t<li>Mode 3: tearing or anti\u2011plane shear\u2014the fracture surfaces move parallel to the leading edge of the fracture and relative to each other (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>c).<\/li>\r\n<\/ul>\r\n<div data-custom-style=\"Captioned Figure\">\r\n\r\n<img style=\"display: block; margin-left: auto; margin-right: auto; ;width: 5.83333in; height: 1.82114in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file134-2.png\" alt=\"\" \/>\r\n\r\n<\/div>\r\n<div data-custom-style=\"Block Text\">\r\n<blockquote>\r\n<div class=\"figcaption-text\">\r\n\r\n<span id=\"X8daf4151ebc66fd2677f8cbafa018550b5f41d0\" class=\"anchor\"><strong>Figure\u00a0132\u00a0\u2011\u00a0<\/strong>Fracture modes based on the stress and the relative displacement (reproduced courtesy of John M. Sharp, University of Texas, Austin).<\/span>\r\n\r\n<\/div><\/blockquote>\r\n<\/div>\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nDifferent fracture modes will result in different fracture properties. Modes 2 and 3 have shear stresses that will affect the walls of the fracture. As a result, asperities will be sheared off and minerals may form on the surface, creating surface features called <em>slickensides<\/em>.\r\n\r\n<\/div>\r\n<div data-custom-style=\"Body Text\">\r\n\r\nAs a fracture forms and propagates through a rock, the stresses that are breaking the rock are distributed throughout the rock so that high compressive stresses occur just ahead of the tip of the fracture. Because of this, when two fractures propagate towards each other, the stresses of each will deflect the direction of propagation for the other fracture (<a href=\"#Xc32a3eeaaa81bb6a6d863e3cfcf6088d050d030\"><span data-custom-style=\"Hyperlink\">Figure\u00a0133<\/span><\/a>).\r\n\r\n<\/div>\r\n<div data-custom-style=\"Captioned Figure\">\r\n\r\n<img style=\"display: block; margin-left: auto; margin-right: auto; ;width: 4in; height: 2.56in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file135-2.png\" alt=\"\" \/>\r\n\r\n<\/div>\r\n<div data-custom-style=\"Block Text\">\r\n<blockquote>\r\n<div class=\"figcaption-text\">\r\n\r\n<span id=\"Xc32a3eeaaa81bb6a6d863e3cfcf6088d050d030\" class=\"anchor\"><strong>Figure\u00a0133\u00a0\u2011\u00a0<\/strong>a) As fractures propagate, high stresses occur just ahead of the fracture tip. b) When the fracture tips get close, the high stress region deflects the direction of propagation.<\/span>\r\n\r\n<\/div><\/blockquote>\r\n<\/div>\r\n<div data-custom-style=\"First Paragraph\">\r\n\r\nStresses that create fractures include the following.\r\n\r\n<\/div>\r\n<ul>\r\n \t<li>Tectonic movements.<\/li>\r\n \t<li>Unloading and exfoliation\u2014when a rock is buried, it is under compressive stress; when the overburden is released, the release of stress causes the rock to fracture.<\/li>\r\n \t<li>Cooling\u2014cooling lava will often contract, creating joint sets that are usually vertical and often result in sets of polygonal columns called <em>columnar joints<\/em>.<\/li>\r\n \t<li>Gravity and freeze\u2011thaw\u2014can cause existing fractures to propagate further.<\/li>\r\n<\/ul>\r\n<\/div>","rendered":"<div id=\"formation-of-fractures\" class=\"level1\">\n<div data-custom-style=\"First Paragraph\">\n<p>There are generally three modes of fracture loading, which involve different fracture surface displacements (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>). The three modes are listed here.<\/p>\n<\/div>\n<ul>\n<li>Mode 1: opening or tensile mode\u2014the fracture faces are pulled apart (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>a).<\/li>\n<li>Mode 2: sliding or in\u2011plane shear\u2014the fracture surfaces slide over each other (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>b).<\/li>\n<li>Mode 3: tearing or anti\u2011plane shear\u2014the fracture surfaces move parallel to the leading edge of the fracture and relative to each other (<a href=\"#X8daf4151ebc66fd2677f8cbafa018550b5f41d0\"><span data-custom-style=\"Hyperlink\">Figure\u00a0132<\/span><\/a>c).<\/li>\n<\/ul>\n<div data-custom-style=\"Captioned Figure\">\n<p><img decoding=\"async\" style=\"display: block; margin-left: auto; margin-right: auto; ;width: 5.83333in; height: 1.82114in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file134-2.png\" alt=\"\" \/><\/p>\n<\/div>\n<div data-custom-style=\"Block Text\">\n<blockquote>\n<div class=\"figcaption-text\">\n<p><span id=\"X8daf4151ebc66fd2677f8cbafa018550b5f41d0\" class=\"anchor\"><strong>Figure\u00a0132\u00a0\u2011\u00a0<\/strong>Fracture modes based on the stress and the relative displacement (reproduced courtesy of John M. Sharp, University of Texas, Austin).<\/span><\/p>\n<\/div>\n<\/blockquote>\n<\/div>\n<div data-custom-style=\"First Paragraph\">\n<p>Different fracture modes will result in different fracture properties. Modes 2 and 3 have shear stresses that will affect the walls of the fracture. As a result, asperities will be sheared off and minerals may form on the surface, creating surface features called <em>slickensides<\/em>.<\/p>\n<\/div>\n<div data-custom-style=\"Body Text\">\n<p>As a fracture forms and propagates through a rock, the stresses that are breaking the rock are distributed throughout the rock so that high compressive stresses occur just ahead of the tip of the fracture. Because of this, when two fractures propagate towards each other, the stresses of each will deflect the direction of propagation for the other fracture (<a href=\"#Xc32a3eeaaa81bb6a6d863e3cfcf6088d050d030\"><span data-custom-style=\"Hyperlink\">Figure\u00a0133<\/span><\/a>).<\/p>\n<\/div>\n<div data-custom-style=\"Captioned Figure\">\n<p><img decoding=\"async\" style=\"display: block; margin-left: auto; margin-right: auto; ;width: 4in; height: 2.56in;\" src=\"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-content\/uploads\/sites\/42\/2026\/05\/file135-2.png\" alt=\"\" \/><\/p>\n<\/div>\n<div data-custom-style=\"Block Text\">\n<blockquote>\n<div class=\"figcaption-text\">\n<p><span id=\"Xc32a3eeaaa81bb6a6d863e3cfcf6088d050d030\" class=\"anchor\"><strong>Figure\u00a0133\u00a0\u2011\u00a0<\/strong>a) As fractures propagate, high stresses occur just ahead of the fracture tip. b) When the fracture tips get close, the high stress region deflects the direction of propagation.<\/span><\/p>\n<\/div>\n<\/blockquote>\n<\/div>\n<div data-custom-style=\"First Paragraph\">\n<p>Stresses that create fractures include the following.<\/p>\n<\/div>\n<ul>\n<li>Tectonic movements.<\/li>\n<li>Unloading and exfoliation\u2014when a rock is buried, it is under compressive stress; when the overburden is released, the release of stress causes the rock to fracture.<\/li>\n<li>Cooling\u2014cooling lava will often contract, creating joint sets that are usually vertical and often result in sets of polygonal columns called <em>columnar joints<\/em>.<\/li>\n<li>Gravity and freeze\u2011thaw\u2014can cause existing fractures to propagate further.<\/li>\n<\/ul>\n<\/div>\n","protected":false},"author":8,"menu_order":71,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1319","chapter","type-chapter","status-publish","hentry"],"part":1512,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1319","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/users\/8"}],"version-history":[{"count":2,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1319\/revisions"}],"predecessor-version":[{"id":1776,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1319\/revisions\/1776"}],"part":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/parts\/1512"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1319\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/media?parent=1319"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapter-type?post=1319"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/contributor?post=1319"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/license?post=1319"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}