ROCKLAND, Maine — Eighteen years ago, one of the largest landslides in state history destroyed two homes in Rockland, forced the evacuation of a third and threatened the road leading to the remainder of the neighborhood.

While that April 16, 1996, landslide on Samoset Road was the costliest one in state history, smaller yet significant slides occur regularly along the Maine coast.

The 1996 landslide occurred on a street adjacent to where a landslide struck 23 years earlier. On Jan. 25, 1973, more than 2 acres were lost in the backyard of two homes along the Waldo Avenue harborfront. No structures were lost in the 1973 landslide, although the 20-foot-high banking came within 20 feet of one home.

No one was injured in either landslide, although Rockland police had to remove an elderly resident from one of the homes that was teetering on the edge before it slid down the embankment in 1996.

While the 1996 landslide received considerable attention across the state, there have been smaller, significant events since then, including in Rockland.

The Maine Geological Survey, which is part of the Department of Agriculture, Conservation and Forestry, states on its Web page that despite the long time between the landslides in Rockland, “their marked similarity indicates that such catastrophic landslides are recurring events in this region, and not isolated ones.”

Michael McMahon can attest to that. McMahon owns a house and nearly 3-acre lot on Waldo Avenue, near where the 1973 slide occurred. McMahon grew up at this Waldo Avenue home and recalls the day of that event 41 years ago because students had been given the day off from school due to the funeral of former President Lyndon Johnson.

Three years ago, a large chunk of McMahon’s backyard facing the harbor slid away into Rockland Harbor. He estimated the size of the lost property as 100 feet long and 50 feet wide.

McMahon spent considerable money last year, an amount he said he did not want to disclose, to shore up the reconfigured banking. The work included placement of riprap to reduce the impact of wave action along the base of the banking. The work was completed last July.

Other property owners along Waldo Avenue and adjacent Samoset Road have also undertaken work to protect their coastal properties. Littlefield Memorial Baptist Church was the first property owner following the 1996 landslide to undertake work to protect the shore from further erosion, again by reducing the steepness of the slope and lining it with riprap.

Stephen Dickson of the Maine Geological Survey said that smaller landslides occur on a regular basis in Maine but most of the time don’t do any damage to structures.

The 1973 landslide occurred during a thawing, wet period in January. Almost exactly a year before the 1996 landslide, a couple who owned a home next to that site had a large chunk of their backyard slide into the harbor. April is often when the ground thaws and both 1995 and 1996 had seen wetter-than-normal conditions.

Dickson said common elements of most landslides are a high water table in marine clay, which makes the soil fluid. In addition, when wave action undercuts slopes, it ultimately will lead to a slide.

“Gravity and a matter of time,” he said.

The Samoset Road slide was caused by similar factors, but on a much smaller scale to the massive landslide in Washington state on March 22, Dickson said. That landslide killed 36 people, with 10 people missing. The erosion in the Washington state landslide was due, in part, to a river eroding the land.

Dickson said dropping the water level in the soils through drainage improvements is one way to reduce the chance of a slide, along with reducing erosion at the base of the slope with the placement of riprap.

The Maine Department of Environmental Protection has seen a number of waterfront owners apply and receive permits for shoring up their waterfront properties to prevent erosion and possible slides. In 2013, 32 permits were issued by the DEP for shorefront stabilization projects. In 2012, 36 such permits were issued and in 2011, there were 44 permits issued.

The Geological Survey lists reported landslides on its Web page. Two of the 11 landslides listed by the agency were the 1973 and 1996 events that occurred in the north end of Rockland’s waterfront.

The largest recorded landslide in Maine in terms of acres was on Nov. 22, 1868, when an estimated 20 acres collapsed into the Presumpscot River in Westbrook. The slide blocked the 200-foot-wide river channel for half a mile, raising the upstream water level at least 15 feet and causing serious flooding, according to the agency’s website.

The 1973 landslide in Rockland occurred during the early morning of Jan. 25 during a spring thaw. The family that lived in the house closest to the slide heard nothing, but awoke to find the new landscape.

On Sept. 28, 1983, a landslide occurred on a bluff at the junction of the Stroudwater River and Indian Camp Brook in Gorham. Seven acres slid into the river and the brook, taking with them a house and garage, several vehicles, a tank truck and a well-drilling rig.

In late March 1997, a landslide occurred at the edge of the coastal bluffs in Brunswick known as Bunganuc. Following the slide in March, the owner’s home measured approximately 100 feet from the edge of the banking.

In May 2005, a landslide occurred in Wells along the banks of the Merriland River. The slide destroyed a portion of a walking trail in the Rachel Carson National Wildlife Refuge and removed the backyard of a nearby house. Parts of the house’s foundation were left exposed and the house was declared unsafe to inhabit.

Another slide occurred in the spring of 2006 along Hobbs Brook in Cumberland along a steeply sloped stream bank. The slide occurred after a heavy, sustained rainfall.

In May 2006, a large earth flow caused by improper drainage due to recent road construction occurred in Sanford, according to the state agency. The drainage focused heavy runoff towards the property, which then undercut the overlying sand, causing a large earth flow into Branch Brook.

A landslide occurred along the Penobscot River in the town of Greenbush on June 30, 2006. The slide undercut Route 2 and caused this section of roadway to be closed until the river bank stabilized, and the roadway section was rebuilt.

Another recent slide was on Patriots Day in 2007 in Buttermilk Cove in Brunswick. No buildings were lost, but a house next to the slope has major cracks in the foundation and basement floor.

On July 9, 2009, a landslide occurred along the Sandy River in Norridgewock, Maine. The slide occurred along a sharp bend on an unpaved section of Sandy River Road, where the road encroaches upon the Sandy River.