Script:
Listen to a conversation between a student and a professor.
M: Hi, Professor Reynolds.
W: Oh. hi, Jeff. I just read your note. You wanted to talk about something?
M: Uh, yeah, just an idea I have. I’ve been thinking— um. I was reading about what’s been going on with those houses on Fox Point.
W: You mean the slide?
M: Yeah, that’s right. The paper said a few days ago there was only one house that was affected, but this morning there was another article saying there were lots more houses involved than they previously thought, maybe as many as fifteen or twenty homes. A couple of houses have big cracks in the foundation.
W: I read the article too. It seems like nothing but bad news for the homeowners.
M: Yeah. My old boss lives out there on Fox Point. I don’t know if his house is one that’s affected. Anyway ... I was ... um ... I was sort of thinking I could write a paper on it. I remember how in your Intro to Geology course we studied gravity movements. I thought maybe ... um ... the slide on Fox Point was a case of subsidence ... um ... when the earth sinks ‘cause there′s a weakening of support. I was thinking this might be an example of settlement.
W: Settlement happens from the more or less gradual compacting of underlying material—for example, when wet soil at the surface dries and shrinks, and creates a depression. It can also happen when frozen ground melts.
M: In class you talked about the Leaning Tower of Pisa.
W: Yes. The settlement that’s caused the Tower of Pisa to lean is due to the failure of a clay layer beneath it. Engineers have been working on it for decades but still haven’t been able to stop the process.
M: There was another kind of settlement you talked about ... um ... when groundwater is removed.
W: Yes. That′s what happened in the San Joaquin Valley in California. Part of the valley floor sank 30 feet because of the removal of groundwater for irrigation. But the problem on Fox Point may not be subsidence at all. This probably has more to do with the slope, and with the amount of rain we’ve been having lately.
M: So ... it’s just a regular old mudslide, not like the Leaning Tower?
W: It’s probably not like the Leaning Tower.
M: The article did say the houses were on a slope, but it’s only slight, it’s not steep at all.
W: Mudslides are most common on intermediate slopes - 27 to 45 degrees — because these slopes are gentle enough for sediment to accumulate and steep enough for sliding. One suggestion I have is to take a look at the county’s Web site. There’s a page on the geology of the region. This area has a history of slides. There was one on Johnson Island about ten, twelve years ago.
M: Oh, really? I didn′t know that. Maybe there’s a connection.
W′: Possibly. It’s an idea to work on.
M: Well, this gives me a place to start. Thanks, Professor Reynolds. I appreciate your input.